STORING AND HANDLING ACIDS

Processing & Handling :: Process Chemicals

October 1, 2012

Acids Handling

General guidelines on materials, storage, pumping and other concerns for the proper and safe handling of acids

Alberto Baumeister Sebastiano Giardinella Mayhell Coronado Ecotek

Inorganic acids play a major role in the chemical process industries (CPI). They are used as raw materials, catalysts or finishing and pH control agents in the manufacture of a wide range of chemical products, from fertilizers to detergents, and even foods. Given their widespread use, a major issue in the CPI is the proper and safe handling of the acids, the adequate materials selection for the pieces of equipment, piping and fittings used in the process, and the correct storage and even disposal of these materials.

These are important factors that need to be taken into account from the design phase throughout the operating life of a facility, in order to ensure there will not be integrity problems that may negatively impact project economical turnover, personnel safety or the environment.
This article covers the most important inorganic acids: sulfuric acid (H₂SO₄), nitric acid (HNO₃), phosphoric acid (H₃PO₄), hydrogen chloride (HCl) and hydrochloric acid, and hydrogen fluoride (HF) and hydrofluoric acid; providing general guidelines on their physical properties, safety data, appropriate materials, storage, pumping and other common issues encountered when handling such fluids in the CPI.

Physical properties

Some acids are naturally present as liquids (H₂SO₄), some are solids at ambient conditions (anhydrous H₃PO₄), and others are gases (HCl, HF). Acids are very soluble in water and thus also widely available as aqueous solutions at different concentrations. Some of these solutions are also enhanced by dissolving additional compounds (for example, fuming sulfuric acid is made by dissolving SO₃ in sulfuric acid).
Given that there are several available grades, the knowledge of physical properties for each one is important in order to avoid freezing, the formation of hazardous fumes, or other problems when storing and handling these materials. The physical properties of the acids covered in this article are briefly presented here. These properties for common available grades are presented in Table 1. Figure 1 plots their vapor pressures at different temperatures.

Table 1. Physical and Chemical Properties of Acids [1–5]

Units

H2SO4

H3PO4

HNO3

HF

HCl

CAS Number

7664-93-9

7664-38-7

7697-37-2

7664-39-3

7647-01-0

Molecular weight

g/gmol

98.079

97.994

63.01

20.01

36.46

Grade

Concen- trated

Fertilizer

Tower

Fuming, 65% oleum

Pure

WFNA

Strong

Common

Gas (anhy- drous)

Aque- ous

Aque- ous

Gas (anhy- drous)

Aque- ous

Aqueous. Technical Grade 22°Be

Concen- tration

wt.%

98

78–80

62–70

35 H2SO4, 65 SO3

75–85

100

90

68

100

48–51

40

100

50

33

Physical state

Liquid

Liquid

Liquid

Liquid

Solid

Liquid

Liquid

Liquid

Gas

Liquid

Liquid

Gas

Liquid

Liquid

Color

Color- less

Color- less

Color- less

Color- less

Color- less

Color- less

Color- less

Color- less

Color- less

Color- less

Color- less

Color- less

Color- less

Color- less

Odor

Odor- less

Odor- less

Odor- less

Odor- less

Odor- less

Pun- gent odor

Pun- gent odor

Disagree- able (can cause choking)

Pun- gent odor

Acrid Odor

Acrid odor

Pun- gent odor

Pun- gent odor

Pun- gent odor

Boiling point (760 mmHg)

°C

340

200

155.85

151.1

212.8

86

120.5

121

20

108

112.2F

–85

100

83

Vapor density (air = 1)

3.4

3.4

2.2

2.5D

0.7

1.97

1.3

0.62

1.267

Specific gravity (H2O=1)

1.83

1.72

1.57

1.56

1.87

1.50

1.50

1.50

1.17

1.14

1.03

1.16

Liquid density (at 20ºC)

g/mL

1.8361

1.7272B

1.6105C

1.5533

1.579A

1.5129

1.4826

1.4048

1.202

1.159

1.251

1.164

Melting point

°C

10.5

–4.29

–36.55

–36.98

42.2

–42

–41.6

–83

–40

–62

–114

–46.2

Dynamic viscosity (at 20ºC)

cP

20.5

6.5

3.52

2.68E

2

Notes: A Liquid Density of phosphoric acid at 75% B Liquid density of sulfuric acid at 80% C Liquid density of sulfuric acid at 70% D Vapor density of nitric acid at 65% E Dynamic viscosity obtained after extrapolation F Boiling point at 38.2%

Figure 1. The vapor pressure as a function of temperature for the acids covered in this article

Sulfuric acid. Sulfuric acid is the single most important inorganic chemical in tonnage produced and in use. H₂SO₄, can be described as a colorless, oily, hygroscopic liquid with no odor; it is the largest inorganic chemical manufactured and one of the most widely used inorganic chemical in the manufacture of many other products. By the year 2004, North America and Asia were the biggest producers of sulfuric acid, recording almost 60% of world total production. Sulfuric acid is manufactured by the combustion of sulfur with dry air to form sulfur dioxide (SO₂), then sulfur trioxide (SO₃) is produced through a catalytic conversion. Finally, sulfuric acid is obtained after absorption of SO₃ in water.
Sulfuric acid is a strong acid and a strong oxidizing agent; therefore it reacts violently with bases, combustible, reducing materials, water and organic compounds with the evolution of heat. It is highly corrosive to most common metals and forms a flammable/explosive gas.
Sulfuric acid is mostly used in the manufacturing of fertilizers, organic pigments, explosives and more. As a strong electrolyte it is used in electroplating baths for pickling, and for operations in the production of iron and steel. Moreover, it is extensively used as a solvent for ores and as a catalyst in the petroleum industry.
Nitric acid. HNO₃ is a solution of nitrogen dioxide (NO₂) in water; it is a colorless to light-brown fuming liquid with an acrid suffocating odor. Nitric acid is the second most important industrial acid; it is a highly oxidizing agent, used in the manufacture of chemicals, explosives, fertilizers, steel pickling and metal cleaning. However, the largest use for nitric acid is for the production of fertilizers.
Nitric acid is a strong acid that reacts violently in the presence of strong bases, reducing agents and combustible fluids, such as turpentine, charcoal and alcohol. It is corrosive to metals, forming flammable or explosive gas. Nitric acid also reacts violently with organic compounds.
Phosphoric acid. H₃PO₄ or orthophosphoric acid is a white solid with a melting point of 42°C, which is highly soluble in water, non-toxic and a relatively weak acid.
H₃PO₄ is the third most important acid in industry. It is used mostly in the production of phosphate fertilizers; but also in the manufacturing of agricultural feeds, soaps, detergents, waxes; and in the food industry as preservative, acidifier, clarifier or flavor enhancer; among other uses.
H₃PO₄ has two main methods of production: the wet process and electric furnace. It is commercially available at concentrations of 75, 80, 85 and 87 wt.% of PO₃. Higher concentrations, such as 105 wt.% (superphosphoric) and 115 to 118 wt.% (polyphosphoric) are also available. “Pure” or “technical grade” phosphoric acid is usually found at 85 wt.%.
Hydrogen chloride and hydrochloric acid. Hydrochloric acid is a solution of the gas hydrogen chloride; it is a poisonous, highly corrosive, hazardous liquid that reacts with most metals to form explosive hydrogen gas. Its appearance varies from pale yellow to colorless, according to purity.
Hydrochloric acid has many applications in the production of organic and inorganic compounds such as fertilizers, chlorides, dyes and more. HCl plays an important role in pickling of steel, acid treatment of oil wells, chemical cleaning and processing, and ore reduction among others.
When boiling all aqueous solutions, HCl forms an azeotropic constant-boiling mixture that contains 20.24% HCl and boils at 110°C (230°F).
Hydrogen fluoride and hydrofluric acid. Anhydrous hydrogen fluoride (AHF) is a clear, colorless, corrosive fuming liquid with an extremely sharp odor. It easily dissolves in water to form hydrofluoric acid.
HF forms dense white vapor clouds if released. Both liquid and vapor can cause severe burns to all parts of the body. Specialized medical treatment is required for all exposures.
HF occurs naturally in volcanic gases and may result from industrial activities, such as coal-burning, and the manufacture or production of aluminum, phosphate fertilizer, steel and other chemical derivatives.
Commercially, HF is used to manufacture fluoropolymers, pharmaceuticals, aluminum, stainless steel, high-octane gasoline, electronics (microchips and printed circuit board cleaning) and uranium isotopes. It is also used to etch glass or metal.

Safety and emergency response

Because acids are mostly hazardous chemicals, their toxicity levels and incompatibilities need to be taken into account when storing and transporting them, as well as how to respond in the event of a spillage.
Permissible exposure limits (PEL) for hazardous materials are given by the U.S. Occupational Safety and Health Administration (OSHA) regulations: 29 CFR 1910.1000, 29 CFR 1926.55 and 29 CFR 1915.1000 for the general, construction and maritime industries, respectively. Other toxicity levels, such as the Recommended Exposure Limit (REL) and Immediately Dangerous to Life and Health Concentrations (IDLH) are published in the U.S. National Institute of Occupational Safety and Health (NIOSH) Pocket Guide to Chemical Hazards. The chemical incompatibilities, health effects and other concerns when handling or storing hazardous chemicals are also given in the NIOSH Pocket Guide.
In the U.S., transportation of these acids or other hazardous materials is subject to the U.S. Department of Transportation Pipeline and Hazardous Materials Safety Transportation regulations. Transportation of hazardous materials in various forms (bulk, pipeline or tank cars) is subject to Title 49 of the Code of Federal Regulations (49 CFR).
In the event of spills of these acids or other hazardous materials, only properly trained personnel such as firemen and policemen (or properly trained plant personnel) should be involved in the emergency response and containment of the product.
The Emergency Response Guidebook 2008 (ERG2008) provides guidelines for managing emergencies when hazardous chemicals are involved. This guidebook is available in printed form, and can also be downloaded in convenient electronic form, including applications for smart phone that allow for quick searches of the chemicals and their associated guides. A new version of the Emergency Response Guidebook is scheduled for release this year (2012).
The chemical safety data for the acids covered in this article, including toxicity levels, incompatibilities and emergency response guides are summarized in Table 2.

Table 2. Toxicity and Emergency Response Data
	H2SO4		H3PO4	HNO3	HF		HCl
PEL (OSHA) [6–8]	1 mg/m3		1 mg/m3 TWA	2 ppm, 5 mg/m3 TWA	3 ppm, 2 mg/m3 TWA		5 ppm, 7 mg/m3 ceiling
REL (NIOSH) [9]	1 mg/m3 TWA		1 mg/m3 TWA; 3 mg/m3 STEL	2 ppm, 5 mg/m3 TWA; 4 ppm, 10 mg/m3 STEL	3 ppm, 2.5 mg/m3 TWA; 6 ppm, 5 mg/m3 (15 min) ceiling		5 ppm, 7 mg/m3 ceiling
IDLH (NIOSH) [9]	15 mg/m3		1,000 mg/m3	25 ppm	30 ppm		50 ppm
Incompatibilities & Reactivities	Organic materials, chlorates, carbides, fulminates, water, powdered metals. Reacts with water to produce heat. Corrosive to metals		Strong caustics, most metals, Reacts with metals to form H2 gas. Do not mix with solutions containing bleach or ammonia	Combustible materials, metallic powders, hydrogen sulfide, carbides, alcohol. Reacts with water to produce heat. Corrosive to metals	Metals, water or steam. Corrosive to metals. Attacks glass and concrete		Hydroxides, amines, alkalis, copper, brass, zinc. Hydrochloric acid is highly corrosive to most metals
UN Listing Number	1830: sulfuric acid; sulfuric acid, with more than 51% acid 1831: sulfuric acid, fuming; sulfuric acid, fuming, with less than 30% free sulfur trioxide; sulfuric acid, fuming, with not less than 30% free sulfur trioxide 1832: sulfuric acid, spent	2796: sulfuric acid, with not more than 51% acid	1805: phosphoric acid; phosphoric acid, liquid; phosphoric acid, solid; phosphoric acid, solution 3453: phosphoric acid, solid	2031: nitric acid, other than red fuming 2032: nitric acid, fuming; nitric acid, red fuming	1052: hydrogen fluoride, anhydrous	1790: hydrofluoric acid	1050: hydrogen chloride, anhydrous 2186: hydrogen chloride, refrigerated liquid	1789: hydrochloric acid; hydrochloric acid, solution
Emergency Response [10]	Guide 137	Guide 157	Guide 154	Guide 157	Guide 125	Guide 157	Guide 125	Guide 157
Notes: PEL: Permissible exposure limit REL: Recommended exposure limit IDLH: Immediately dangerous to life or health concentration TWA: Total weighted average STEL: Short time exposure limit ERG: Emergency Response Guidebook

Materials selection

The materials of construction, as well as any lining or internal coating requirements should be determined by a materials expert based on the acid, its concentration and storage conditions.
Aqueous acid solutions are very corrosive, and usually require special materials depending on the temperature or phase.
Some recommendations are given regarding the correct material selection depending on acid, such as in the following reference for H₂SO₄: NACE RP0391 — Materials for the Handling and Storage of Concentrated (90 to 100%) Sulfuric Acid at Ambient Temperatures; HF: NACE 5A171 — Materials for Storing and Handling Commercial Grades of Aqueous Hydrofluoric Acid and Anhydrous Hydrogen Fluoride.
Depending on the acid and storage, transport or process conditions, interior coatings or linings could also be considered. For instance, rail tank cars transporting concentrated sulfuric acid should be internally coated according to NACE SP0592 — Application of a Coating System to Interior Surfaces of New and Used Rail Tank Cars in Concentrated (90 to 98%) Sulfuric Acid Service.
Tables 3–8 list some common metal alloys used in the CPI, along with their general acceptable use ranges (concentrations and temperatures) for each of the acids covered in this article.

Table 3. Materials of Construction, Cladding & Lining [12]
Materials of construction	H2SO4
Aluminum	Aluminum alloys may be used to handle dilute (concentration below 10%) and concentrated acid (above 98%). It suffers corrosion for handling sulfuric acid in a range of concentration of 40–95 %
Carbon steel	It can be used to handle concentrated sulfuric acid at ambient temperatures under static and low-velocity condition. Corrosion resistance depends on temperature, acid concentration, iron content and flowrates
Cast Iron	Alloys with 14.5% content of silicon have shown best resistance to corrosion for sulfuric acid handling in all concentrations at temperatures up to the boiling point
Copper	Copper and copper alloys are not suitable for sulfuric acid handling
Lead	It has shown high resistance to corrosion in sulfuric acid handling up to 70% concentration. Although, this material is not recommended for pumps or valves
Nickel	Nickel 200 demonstrates good tolerance to sulfuric acid when it is handled at low or moderate temperatures
Niobium	It can be used for handling sulfuric acid at concentrations below 95% under oxidizing conditions
Gold	Exhibits excellent resistance to sulfuric acid up to 250°C (480°F) and is used when no corrosion can be tolerated
Platinum	Resists sulfuric acid in all concentrations and temperatures
Palladium	It is attacked by sulfuric acid in the presence of air
Rhodium	In wrought or cast form rhodium is not recommended for handling sulfuric acid
Stainless steel	Concentrated sulfuric acid turns extremely corrosive in presence of 316 and 304 stainless steels. The conventional austenitic grades show good resistance in dilute or highly concentrated acid at moderate temperatures
Zinc	It is slowly dissolved by dilute sulfuric acid; corrosion resistance depends on the concentration of the acid and the purity of the metal

Table 4. Materials of Construction, Cladding & Lining [12]
Materials of construction	H3PO4
Aluminum	Aqueous solutions of phosphoric acid with concentration of 5 to 85% are highly corrosive for alloys 1100. Consequently this material is not recommended for phosphoric acid handling
Cast Iron	All cast irons can be considered to handle phosphoric acid; although the presence of contaminants must be previously evaluated since it can provoke severe cases of corrosion. High-silicon cast irons are ideal to manage phosphoric acid in all concentrations at any temperature, no presences of fluoride ions (F-) are allowed
Copper	Copper and copper alloys can be used to manage pure phosphoric acid solutions in heat-exchanger tubes, pipes and fittings. System impurities can accelerate the rate of corrosion more than acid concentration
Lead	It is extensively used in the manufacture of phosphoric acid. It is highly resistant to corrosion
Nickel	Nickel alloys are appropriate for handling phosphoric acid. For dilute acid alloys 20Cb-3 and 825 are recommended; for concentrated acid at high temperatures alloy B-2 offers the highest corrosion resistance
Niobium	Resistant to corrosion for handling acid at temperatures below 100°C in all concentrations
Silver	Resistant to corrosion for handling acid at temperatures between 160 and 200°C in all concentrations
Tantalum	Resistant to corrosion for handling acid at temperatures up to the boiling point in all concentrations in absence of fluoride ions (F)
Stainless Steel	Conventional austenitic stainless steel has shown elevated corrosion resistance for all concentrations of phosphoric acid up to 65°C (150°F)

Table 5. Materials of Construction, Cladding & Lining [12]
Materials of construction	HNO3
Aluminum	Aluminum alloys commonly used for nitric acid services are 1100 and 3003. Corrosion depends on temperature and concentration of the acid. Aluminum alloys are compatible with nitric acid at temperatures up to at least 71°C (160°F) when it is inhibited by hydrofluoric acid
Cast iron	Cast iron can be used for handling concentrated nitric acid under control conditions such as low temperature and low velocity. Corrosion attacks when handling dilute nitric acid
Stainless steel	For concentrations of 0 to 65%, most AISI 300-Series stainless steel has shown great corrosion resistance for temperatures up to the boiling point
Copper	Not suitable for use in nitric acid
Lead	It can be used for concentration between 52 and 70%
Molybdenum	Not suitable for use in nitric acid
Nickel	Nickel alloys are widely used in the production of nitric acid. Alloy 617 offers an excellent performance and corrosion resistance for handling nitric acid at high temperatures in the catalyst-support grids in high pressure plants
Niobium	It is completely resistant to nitric acid in all concentration at temperatures below 100°C
Gold	It is resistant to nitric acid in concentrations up to 50% above that it is attack by corrosion
Palladium	It is vulnerable to attack from corrosion when nitric acid is in presence of air
Rhodium	In wrought or cast form rhodium is resistant to corrosion produced by concentrated nitric acid at 100°C
Silver	Not suitable for use in nitric acid
Tin	Not suitable for use in nitric acid. Complex reaction occurs
Titanium	Appropriate for handling nitric acid at any concentration in temperatures below the boiling point. As temperatures exceed 80°C (175°F), corrosion becomes stronger depending on nitric acid purity. Titanium alloys can’t be used for red fuming nitric acid due to a violent reaction that can take place in the system

Table 6. Materials of Construction, Cladding & Lining [12]
Materials of construction	HF
Aluminum	Unsuitable for handling hydrofluoric acid
Stainless steel	Stainless-steel type 304 has a good performance for handling anhydrous hydrogen fluoride up to 200°C (390°F), it has poor resistance to dilute or concentrated hydrofluoric acid. On the other hand stainless-steel type 316 can be used for handling dilute acid at low temperatures
Copper	The use of copper alloys is affected by aeration and velocity, its corrosion resistance depends on the concentration and temperature
Lead	Fair corrosion resistance in a wide range of concentration and temperatures for handling hydrofluoric acid. Not recommended for handling dilute acid
Molybdenum	It offers great corrosion resistance to aqueous and anhydrous hydrofluoric acid with concentrations up to 50%, below 100°C (212°F)
Nickel	Nickel 200 is ideal for handling hot anhydrous hydrogen fluoride vapor, but it is not recommended for handling hydrofluoric acid in aqueous solutions
Niobium	Unsuitable for handling hydrofluoric acid
Tin	Unsuitable for handling hydrofluoric acid
Titanium	Unsuitable for handling hydrofluoric acid
Zirconium	Unsuitable for handling hydrofluoric acid

Table 7. Materials of Construction, Cladding & Lining
Materials of construction	HCl
Aluminum	It is not appropriate for handling HCl; it has no resistance to corrosion
Cast Iron	Unalloyed cast iron systems are unsuitable for handling HCl, especially if high velocities are involve. A high-silicon iron alloyed with small amounts of molybdenum, chromium and copper can be used to handle hydrochloric acid up to 95° C (200°F) at all concentrations
Stainless steel	Corrosion attacks stainless steel (316) and stainless steel (304) when handling HCl at any concentration or temperature
Copper	Copper can be used to handle dilute hydrochloric acid only, due to its sensitivity to velocity, aeration and oxidizing impurities
Lead	It exhibits tolerance to corrosion at 24°C (75°F) and concentrations up to 15%. It is unsuitable for concentrated acid at higher temperatures
Nickel	Pure nickel and nickel-copper alloys can be used for handling hydrochloric acid below 10% concentration, without air presence, at low temperatures. The lower the concentration the higher can be the temperature of the system; for example, HCl at 0.5% can stand temperatures up to 200°C before corrosion attacks the alloy
Niobium	It has shown excellent corrosion resistance to handle HCl at any concentrations and temperatures up to 100°C (212°F)
Gold	It can be used for handling hydrochloric acid at any concentrations and atmospheric pressure up to the boiling point
Palladium	Unsuitable for handling hydrochloric acid
Rhodium	In cast or wrought form, rhodium has excellent corrosion resistance to handle concentrated hydrochloric acid in temperatures up to 100°C (212°F)
Silver	It is very susceptible to aeration when concentration and temperature are high
Tantalum	It has shown excellent corrosion resistance to handle HCl at any concentrations under atmospheric pressure and temperatures up to 90°C (195°F). It can be used to handle acid with concentrations below 25% up 190°C (375°F)
Titanium	Unsuitable for handling hydrochloric acid

Table 8. Materials of Construction, Cladding & Lining
ACIDS	COMMON ALLOYS
H2SO4	For dilute and intermediate sulfuric acid (between 40 and 80% concentration) Incoloy alloys 25-6MO, 825, 020 and Inconel alloy G-3 have shown excellent corrosion resistance for temperatures up to 50 °C (120°F). When handling aggressive acid, Inconel alloys 625, 622, C-276 and 686 are suitable. For reducing conditions, Monel alloy 400 is appropriate in the absence of air for temperatures up to boiling point for concentrations below 15%. For storage of H2SO4, Monel alloy 400 can be used at room temperatures up to 80% concentration. Hastelloy B3, C-2000 and G-30 are also suitable for handling sulfuric acid
HNO3	Chromium enhances corrosion resistance in alloys while handling nitric acid, due to this fact, Incoloy alloy 800 and 825 are adequate for nitric acid at all concentrations for temperatures up to the boiling point. Inconel alloy 600 and C-276 also offer good corrosion resistance to nitric acid for concentration over 20% at room temperature; alloy 690 has shown better corrosion resistant because its chromium content is higher. Hastelloy G-30 alloy and G-35 offer excellent corrosion resistance for this same reason
H3PO4	When handling phosphoric acid, Incoloy alloys 825, 020 and 25-6MO, as well as Inconel alloy G-3 are suitable and regularly used. For extreme conditions such as high temperature and high amount of impurities or halides contaminants, Inconel alloys 625, 622, C-276 and 686 are recommended. Hastelloy alloys B-3 and G-30 stand phosphoric acid in all concentrations and temperatures. Hastelloy alloy G-35 was especially designed for phosphoric acid wet processing in fertilizers manufacture
HCl	Incoloy alloys 25-6MO, 825 and 020, and Inconel alloy G-3 are used for dilute hydrochloric acid handling. Another alloy that offers good corrosion resistant in concentrations below 10% with aerated conditions at room temperature is Monel alloy 400. Nickel alloy 200 can be used at room temperature for concentrations up to 30% as well. For environments that contemplate the presence of oxidizing contaminants and hot hydrochloric acid, Inconel alloys 625, 622, C-276 and 686 are recommended. Hastelloy alloys B-3, C-2000 and G-30 are also suitable for handling hydrochloric acid, at all concentrations and temperatures
HF	The formation of fluoride films is key on engineering materials in order to offer good corrosion-resistance rates while handling hydrofluoric acid. Monel alloy 400 is widely used for this purpose, due to the fact that it has shown excellent corrosion resistance for all hydrofluoric acid services in all concentrations and temperatures up to (and even above) the boiling point. For anhydrous hydrogen fluoride up to 82°C (180°F), Nickel alloy 200 is commonly used. For dilute HF and temperatures up to 70°C (158°F) Inconel alloy 600 can also be used. Other alloys like Hastelloy C-2000 and Hastelloy G-30 are also recommended for handling hydrofluoric acid

Storage tanks

Usually aboveground storage tanks (ASTs) are used to store acid as they facilitate accessibility to tanks and ancillary equipment for inspection and maintenance. The storage tank should be sized for at least 50% more volume than required.
Tanks for acid storage are usually built of either metal (lined or non-lined), or fiber reinforced plastic (FRP). Metal tanks offer a higher durability, and can also resist higher stresses or impacts; whereas FRP tanks are economical, usually chemically inert, and can be a good alternative for low-volume, short storage times.
The mechanical design of tanks for acid storage usually follows either of the following codes:
• API STD 650 — Welded Steel Tanks for Oil Storage: for vertical tanks with flat bottoms and operating pressures less than 0.14 barg (2.5 psig)
• API STD 620 — Recommended Rules of Construction of Large, Welded, Low Pressure Storage Tanks: for vertical tanks with flat bottoms and operating pressures between 0.14 barg and 1.03 barg (2.5 psig and 15 psig)
• ASME BPV Code, Sect VIII, Div 1: for other operating pressures
Special design criteria, such as particular corrosion allowances or nozzle design, are also considered in acid storage tanks — either by special company or supplier criteria, or from professional associations. For instance, concentrated sulfuric acid tanks design should follow NACE SP0294 — Design, Fabrication, and Inspection of Storage Tank Systems for Concentrated Fresh and Process Sulfuric Acid and Oleum at Ambient Temperatures.
Tanks should allow access to the top nozzles and the vent system, and offer an appropriate facility for sampling. Periodically, it is necessary to homogenize the contents of the tank, because the acid that remains on the surface establishes a vapor-liquid equilibrium in which toxic and corrosive gases are released, so a recirculation system is recommended.
Special attention should be given to the acid physical properties in storage to prevent freezing, high corrosion rates or vaporization.
In general, corrosion rates increase at higher temperatures, so acids should be stored at the lowest possible temperature without freezing the acid. Higher corrosion rates could also result from heating of the metal surfaces due to sun radiation, so the tank exterior should be painted with a radiation reflecting color, such as white. Another regular measure to maintain acids at an appropriate temperature is coating the tank with an adequate material such as vinyl-based materials.
In places where the storage temperature could be below the acid freezing point, storage tanks and vessels should be provided with heating facilities, such as plate coils mounted on the outside of the tank wall, or external heat exchangers connected to the tank. Internal heating coils are not recommended, because excess temperature in the coil walls accelerates corrosion and could cause leaks. Also, high-pressure steam is not recommended as a heating medium since heat exchange surfaces could exceed 100°C, causing severe corrosion.
Pressurized storage is required when the vapor pressure exceeds the atmospheric pressure at the storage temperature.
Common guidelines for acid storage tank design are summarized in Chem. Eng. May 2008, Facts at your Fingertips: Acid Storage.
When storing acids above ground, containment is also an issue. Tanks should be properly diked, or double walled, to contain spills. In general, containment should be at least for one tank volume (if not properly drained), or less provided there is adequate drainage to an acid neutralization pit, with blockage valves accessible to operators. Local code requirements should also be addressed when designing acid-tank containment; for instance, the U.S. State of Florida has specific requirements as given by Rule 62-762.891 — Mineral Acid Storage Tank Requirements.

Pumps

The design basis should be set before selecting a pump, that is, the operating conditions such as temperature, suction pressure, acid concentration, and so on.
A primary issue that must be taken into account while pumping acids is safety, so, the selected pump for the system cannot leave place for leakage; this is an advantage regularly offered by vertical submerged pumps over horizontal pumps. Also, material selection guidelines shall be followed to avoid casing, impeller or other internals damage.

Piping and fittings

Selecting pipe material and designing the pipe system is a very important issue in a plant, especially while handling acids. The system must ensure the acid is transported safely and efficiently. Piping should have as few flanges as possible, so the chance of having leaks becomes negligible.
In order to select the piping material, the following aspects have to be defined: acid concentration, transport temperature, phase, fluid velocity, type of flow, impurities in the acid and solids presence.
Corrosion is often related to an acid’s velocity. In order to maintain a low velocity of the fluid, a bigger pipe diameter is suggested.

Valves

Valves are used for various functions, including the following:
For blocking, gate valves or plug valves are regularly used. However, plug valves are preferred for this service, to ensure proper valve operation.
For control, globe or butterfly valves are suitable; they can be manually operated or be fitted with actuators.
Materials for different parts of the valves (disk, stem and seat) should be selected according to the acid concentration and operating conditions, by consulting the valve manufacturer.
Some common materials according to the acid to be handled are presented in Tables 9–13.

Table 9. Specific Equipment, Piping, Valves and Protective Clothing Guidelines
Equipment	H2SO4
Tanks	Iron sulfate is produced in storage tanks of sulfuric acid; it is a consequence of interaction between the tank’s surface and the acid. Usually iron sulfate precipitates, therefore the pump suction pipe should be placed above the tank bottom to avoid pumping solid residues that can compromise pump well-functioning. Under the same line, storage tanks must provide a facility to clean the tank bottom. The tank’s maintenance should be performed periodically according to the laws of the state and the company policies
Pumps	According to the plant requirements, pumps used for sulfuric acid handling are usually horizontal centrifugal pumps or heavy duty vertical, submerged type For handling sulfuric acid at 93.19% (66 °Bè) usually horizontal centrifugal pumps with mechanical seals are used Common materials of construction are: cast iron or Alloy 20 wetted ends, Alloy 20 plunger, tetrafluoroethylene plastic chevron packings
Piping and fittings	For sulfuric acid service, welded pipe lines with schedule 80 are commonly used, these pipes should be kept full of acid to minimize corrosion attacks. Sulfuric acid also promotes hydrogen gas formation; for this reason it is necessary to avoid pressure buildup by venting the line In case of draining the pipe, the use of air is not recommended, because it can accelerate corrosion. Nitrogen can be used for such purposes
Valves	Butterfly Valves: Lead is an adequate stem and disk material for sulfuric acid at all concentrations; for concentrations lower than 75% at low temperatures Alloy 20 and Hastelloy have also been used. The seat should be made of PVF, with Viton and Hypalon also been used
Protective clothing	Properly fitted chemical safety goggles, face shield (8-in. high minimum) and protective clothing should be worn. Acid-proof clothing should be fitted snugly at neck and wrists, in a manner preventing drainage of acid to gloves or boots. Impervious rubber or polyvinyl chloride gloves with gauntlets covering forearms should be used. Boots made of the same material should be worn, with tops being covered by the trousers. Head protection via hard hat or full cover acid hood should be worn, as well as a respirator for protection against fumes

Table 10. Specific Equipment, Piping, Valves and Protective Clothing Guidelines
Equipment	H3PO4
Tanks	Heating coils should be provided in order to maintain the phosphoric acid above its freezing point, depending on ambient conditions and acid concentration. For instance, 85% H3PO4 freezes at 21.1°C
Pumps	All fittings should have wetted parts of 316 L stainless steel, with mechanical seals rather than packing. Centrifugal pumps are also used for phosphoric acid handling
Piping and Fittings	Stainless steel 316 is regularly used for piping because it has shown excellent results in corrosion resistance for all concentrations of phosphoric acid, even though the piping material can be the same used for storage When using stainless steel, the fittings and valves should be welded or flanged; screwed fittings are not recommended because they may allow leakage
Valves	Butterfly valves: 316 SS, Alloy 20 and Hastelloy C are good stem and disk materials for phosphoric acid at various concentrations, with Monel also showing fair results. Common seat materials include: PVF, Neoprene, Hypalon, Viton or EPT
Protective Clothing	Properly fitted chemical goggles and protective clothing should be worn. Impervious gloves and aprons are recommended. No special respiratory protection is required under ordinary conditions of use, provided that adequate ventilation is maintained. When vapor or mist concentrations exceed applicable standards, approved respiratory protective equipment must be used

Table 11. Specific Equipment, Piping, Valves and Protective Clothing Guidelines
Equipment	HNO3
Tanks	For acid grades lower than 95 wt.%, tanks should be designed for slight pressure and vacuum, with fumes collected at a disposal system and sent to a scrubber. Vent piping should be designed taking into consideration possible corrosion from contact with moisture
Pumps	Wetted parts should be made of 304L stainless steel for concentrations lower than 95 wt.%; for higher concentrations, they should be made of titanium (with a water content higher than 1.34% to prevent spontaneous combustion), silicon iron or 3003 aluminum alloy [11]
Piping and Fittings	Piping made of 304L stainless steel is frequently used for HNO3 up to 95 wt.%, and of aluminum for higher concentrations. Carbon steel (CS) piping with TFE, FEP or glass linings (up to certain temperatures) can also be used for all grades. [11]
Valves	Butterfly valves: 316 SS, Alloy 20 and Hastelloy C are good stem and disk materials for nitric acid at various concentrations. Seats made of Viton can handle various concentrations up to 70%; for low concentrations at low temperatures, Neoprene, Hypalon and EPT have also been used
Protective Clothing	Neoprene or natural rubber latex gloves are acceptable for handling nitric acid.

Table 12. Specific Equipment, Piping, Valves and Protective Clothing Guidelines
Equipment	HF
Tanks	Anhydrous and 70 wt.% HF up to 66°C, or HF between 60 to 70 wt.% up to 38°C, can be stored in carbon steel (CS) tanks, since the metal is passivated with an iron fluoride film when the fluid is in contact with the metal. Hydrogen corrosion may occur in steel tanks. Other grades of HF can be stored in tanks made of CS with natural rubber lining, polyethylene or unplasticized PVC [11]
Pumps	Diaphragm pumps with TFE or polychlorotrifluoroethylene (CTFE) diaphragms can handle anhydrous, 70 wt.% and electronic-grade HF. Centrifugal pump materials depend on grade: Ni-Cu alloy of Alloy 20 is used for anhydrous HF, Vinylidene chloride (VC)-lined steel for 70 wt.% and electronic-grade HF, and Penton-lined steel or solid Penton for electronic grade HF [11]
Piping and fittings	Anhydrous and 70% wt HF can be transported in seamless CS piping. The rating and schedule should be selected according to the operating pressure and corrosion allowance, with Sch 80 and Sch 160 commonly used for both grades, respectively. CS with VC, TFE and FEP lining is also used, depending on fluid temperature. Electronic-grade HF can be transported in unplasticized PVC pipe
Valves	Butterfly valves: Hastelloy C is the best material for the stem and disk, with Alloy 20 also exhibiting fair results. Common seat materials include: PVF, Hypalon and Viton; for pure (100%) HF, only PVF or Viton should be considered
Protective Clothing	Neoprene and natural rubber gloves are excellent for handling hydrofluoric acid in all concentrations, glove change is necessary before 8 hours

Table 13. Specific Equipment, Piping, Valves and Protective Clothing Guidelines
Equipment	HCl
Tanks	Outdoor tanks are preferred for storing hydrochloric acid; some common measures of protection when tank is placed indoors are coating the floor with asphalt or another corrosion resistant material to prevent several damages in case of leaks or spills. The tank must be provided with a vent so acid fumes do not accumulate in the tank and a drainage system so maintenance can be performed periodically. Vents should be routed to a scrubber
Pumps	Pumps similar to those used for H2SO4 and H3PO4 can be used. Centrifugal pumps lined with, or constructed of TFE, PVDF of Derakane are commonly used. Mechanical seals of carbon and ceramic faces with TFE or fluoroelastomer secondary seals, and Hastelloy C metal parts, are also recommended [11]
Piping and fittings	CS piping with TFE, PVDF, Derakane or polypropylene lining is frequently used for HCl. PVC or FRP piping have also been used, depending on fluid pressure
Valves	Butterfly Valves: common stem and disc materials include: lead or Hastelloy C. Common seat materials include: PVF, Neoprene, Hypalon and Viton
Protective clothing	For concentrations up to 40% neoprene and fluoroelastomer gloves are recommended for handling hydrochloric acid. For concentrated acid, butyl gloves are suitable

Acid handling

Sulfuric acid. Sulfuric acid must be stored separately from combustible and reducing substances in a well-ventilated environment at temperatures below 23°C (73.4°F). Concentrated acid needs to be isolated from water, as it may react violently, releasing heat. If sulfuric acid needs to be diluted or combined with water, then it has to be added to water carefully.
To manipulate sulfuric acid, proper personal protective equipment, such as gloves, a vapor respirator when ventilation is inadequate, face shield and full suit shall be used.
Nitric acid. Nitric acid must be stored separately in a corrosion resistant location, avoiding contact with powders, carbides, hydrogen, sulfide, turpentine and strong bases. Along the same lines it is important to mention that nitric acid’s storage requires special conditions, such as adequate ventilation and especially low temperatures to ensure a cool environment for the solution, because heat may cause containers to burst and result in escape of poisonous gases; so it should not be stored above 23°C (73.4°F), and the container must remain dry and locked up.
Nitric acid and its vapors can cause severe damage during its handling to persons who have contact with it; the severity of the damage is related to the time of contact or exposure and the acid concentration.
Every process that involves nitric acid handling or storage must contemplate an adequate ventilation system that ensures airborne levels below the safety exposure limits allowed, not only this measure needs to be taken into account but also workers should be aware of the risks arising from management of nitric acid.
Phosphoric acid. Phosphoric acid can be described as a stable chemical, because it is not subject to thermal decomposition. However, the design criteria for its handling should be based on the acid concentrations and operating temperatures. The most important issue about this acid is the variation of its freezing point according to its concentration; the freezing point of standard concentrations are –17.5°C (0.5°F) at 75%, 4.6°C (40.2°F) at 80% and 21.1°C (70.01°F) at 85%, therefore it becomes necessary to heat phosphoric acid at high concentrations in order to maintain the acid as a liquid solution.
Unlike other acids, phosphoric acid does not react violently with metals; reaction occurs slowly and progressively with hydrogen as a product, so, caution should be exercised because the vapors formed are flammable.
Hydrofluoric acid. HF acid is a very hazardous material, both in liquid and vapor phase. It can cause severe burns, which may not be immediately painful or visible. HF is a strong irritant to the skin, eyes and respiratory tract. The fluoride ion easily penetrates the skin and generates destruction of tissue and severe bone damage.
Package sizes range from 500–1,000 mL for analytical products, to 10,000-L ISO containers. HF is delivered commercially in concentrations of 98 wt.%, 48–51 wt.% and 40 wt.%.
Due to HFs nature, strict measures shall be taken when handling the acid in industrial facilities. Such measures include administrative controls (for example, work permits); engineering controls (instrumentation: detectors, relief valves, emergency dump systems); and personal protection equipment (appropriate clothing).
When boiling all aqueous solutions, HF forms an azeotropic constant boiling mixture that contains 35.6% (by weight) HF and boils at 111.35°C (231.8 °F).
Hydrochloric acid.HCl must be stored in a corrosion resistant location. Even though the acid is non-flammable, when it is heated hydrochloric acid fumes are released, which can compromise the safety and toxicity levels allowed, therefore storage tanks need proper venting that shall be directed to a safe location and treatment facility.
Operators handling hydrochloric acid must wear protective equipment and it is advisable for them to take a shower and gargle with sodium bicarbonate after manipulating the acid in order to avoid teeth corrosion in other activities performed by the operator.
Undesirable reactions can take place between hydrochloric acid and the following compounds: chromate, permanganate and sulfate. Such reactions generate chlorine gas as a result. A subsequent reaction occurs with metal peroxide forming its corresponding chloride.
When storing hydrochloric acid, proper ventilation has to be ensured in order to maintain the acid concentration in air below the permitted limit of exposure.
Edited by Gerald Ondrey

References

1. Perry, R., Green, D. W., & Maloney, J. O. Perrys Chemical Engineers Handbook, McGraw-Hill, N.Y., 2008.

2. Davenport, W. G., and King, M. J., Sulfuric Acid Properties, In Sulfuric Acid Manufacture: Analysis, Control and Optimization, Elsevier, pp. 287–291, 2006.

3. DKL Engineering, Inc.,. Technical Manual, April 12, 2003. Retrieved July 6, 2012, from Sulfuric Acid Properties: www.sulphuric-acid.com/techmanual/Properties/proper ties_acid_properties.htm

4. Material Safety Data Sheet, Nitric acid, 65% MSDS.

5. Potash Corp., Purified Phosphoric Acid, Technical information bulletin, PCS Sale — Industrial Products, 2005.

6. U.S. Dept. of Labor, Occupational Safety and Health Administration (OSHA). Retrieved May 14, 2012, from Regulations: 29 CFR 1910.1000 (General Industry): www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=Standards&p_id=9991

7. U.S. Dept. of Labor, Occupational Safety and Health Administration (OSHA), Retrieved May 16, 2012, from Regulation: 29 CFR 1926.55 (Construction Industry): www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=Standards&p_id=10628

8. U.S. Dept. of Labor, Occupational Safety and Health Administration (OSHA), Retrieved May 16, 2012, from Regulation: 29 CFR 1915.1000 (Maritime): www.osha.gov/pls/oshaweb/owadisp.show_document

9. National Institute of Occupational Safety and Health, NIOSH Pocket Guide to Chemical Hazards, NIOSH Publications, 2007.

10. U.S. Dept. of Transportation, Emergency Response Guidebook 2008 (ERG2008), 2008.

11. Grossel, Stanley S., Safe, Efficient Handling of Acids, Chem. Eng., July 1998, pp. 88–98.

12. ASM International, (2002). Handbook of Corrosion Data, 2002.13. API Std. 620.

14. API Std. 650.

15. ASME Boiler and Pressure Vessel Code Sec. VIII Div 1.

16. DKL Engineering, Inc., Technical Manual, December 20, 2005, Retrieved July 6, 2012, from Strong Acid System — Piping, www.sulphuric-acid.com/techmanual/strong%20acid/sa_piping.htm

17. International Program on Chemical Safety, Chemical Safety Information from Intergovernmental Organizations, April 2000, Retrieved May 12, 2012, from Hydrogen Chloride: www.inchem.org/documents/icsc/icsc/eics0163.htm

18. Pohanish, R. P., Sittigs Handbook of Toxic and Hazardous Chemicals and Carcinogens”, Elsevier, 2012.

19. Southerm States Chemical A Dulany Industries Co., Chemical Safety Handbook, 2002.

20. The Dow Chemical Company, June 2008, 2008, Retrieved July 9, 2012, from Product Safety Assessment: Nitric Acid: http//msdssearch.dow.com/publishedliteratureDOWCOM/dh_0131/0901b80380131028.pdf?filepath=productsafety/pdfs/noreg/233-00312.pdf&fromPage=GetDoc

21. U.S. Dept. Transportation, Electronic Code of Federal Regulation. Retrieved May 14, 2012, from Chapter I Pipeline and Hazardous Materials Safety Transportation regulation: ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&tpl=/ecfrbrowse/Title49/49cfrv2_02.tpl

Authors

Alberto Baumeister is the CEO and co-owner of the Ecotek group of companies, which is located in the City of Knowledge, Panama (Calle 60, PH Obarrio 60, Piso 15, Ofc. 15-A, Obarrio, Panamá, Rep. De. Panamá; Phone: +507-203-8490; Fax: +507-203-8491; Email: abaumeister@ecotekgrp.com). He has experience as coordinator and senior process consultant in engineering projects for the chemical, petrochemical, refining, oil and gas industries. He has a Master’s Diploma in water treatment management from Universidad de León (Spain, 2011), a specialization in management for engineers at Instituto de Estudios Superiores de Administración (Venezuela, 1990), and a degree in chemical engineering from Universidad Metropolitana (1987), graduating first of his class. He has been a professor of the Chemical Engineering School at Universidad Metropolitana between 1995 and 2007 and has written several technical publications for international associations.

Sebastiano Giardinella is the vice president and co-owner of the Ecotek group of companies (same address as above; Email: sgiardeinella@ecotekgrp.com). He has experience as process leader, and in project planning and control, in engineering projects for the chemical, petrochemical, refining, oil and gas industries. He is a certified project management professional (PMP), has Master’s Degree in project management from Universidad Latina de Panamá (Panama, 2009), and a degree in chemical engineering from Universidad Simón Bolívar (Venezuela, 2006), graduating summa cum laude; and is currently a student of the M.Sc. in renewable energy development at Heriot-Watt University (Scotland). He is also professor of project management at Universidad Latina de Panamá, and has written technical publications for Chemical Engineering magazine, international associations and academic institutions.

Mayhell Coronado is a process engineer of the Ecotek group of companies (same address as above; email: mcoronado@ecotekgrp.com). She has experience in the development of conceptual and basic engineering projects for the oil and gas, and chemical industries, as well as in support to company management. She has a degree in chemical engineering from Universidad Metropolitana (Venezuela), where she taught thermodynamics, transport phenomena and general chemistry as professor assistant, and has published a work on the effects of microbial contamination in diesel fuel used for thermal power generation.

Click here for full pdf version of this article - includes all graphs, charts, tables, and author information

SILVER DISINFECTANTS.....

Silver as a Residual Disinfectant To Prevent Biofilm Formation in Water Distribution Systems▿

1. Nadia Silvestry-Rodriguez1,
2. Kelly R. Bright2,
3. Donald C. Slack3,
4. Donald R. Uhlmann4 and
5. Charles P. Gerba2,*

+ Author Affiliations

1. ¹Department of Agricultural and Biosystems Engineering, Room 403, Building 38, The University of Arizona, Tucson, Arizona 85721
2. ²Department of Soil, Water and Environmental Science, Room 429, Building 38, The University of Arizona, Tucson, Arizona 85721
3. ³Department of Agricultural and Biosystems Engineering, Room 403, Building 38, The University of Arizona, Tucson, Arizona 85721
4. ⁴Arizona Materials Laboratory, Department of Materials Science and Engineering, The University of Arizona, 4715 E. Fort Lowell Road, Tucson, Arizona 85712

Next Section

ABSTRACT

Biofilms can have deleterious effects on drinking water quality and may harbor pathogens. Experiments were conducted using 100 μg/liter silver to prevent biofilm formation in modified Robbins devices with polyvinyl chloride and stainless steel surfaces. No significant difference was observed on either surface between the silver treatment and the control.

The materials used in drinking water distribution systems are readily colonized by bacteria (5). The rates of biofilm formation and release into a distribution system (DS) can be affected by many factors (14). Although few biofilm organisms pose a threat to humans, many opportunistic pathogens are able to survive and proliferate (40).

Chlorination is a commonly used water treatment in the United States and Europe (41). Chlorine is also used to provide a residual disinfectant in the DS to prevent water recontamination and to maintain the standards achieved at the first point of disinfection (4). Once a biofilm is established, however, bacteria are more resistant than planktonic populations to disinfectants, including chlorine (16, 20, 32, 44), and antibiotics (25).

Factors affecting survival in biofilms in chlorinated water include low-nutrient conditions, strain variation, bacterial attachment to surfaces with concomitant metabolism changes, and bacterial encapsulation (1, 19, 43). Biofilm growth can lead to pipe corrosion (24, 27), deterioration in water quality (24) and aesthetics (27, 36), and other undesirable effects (24). Chlorine also produces harmful disinfectant by-products (46), particularly with high levels of organic matter. Free chlorine creates problems in older DSs by causing pitting corrosion. Precipitation of ferric hydroxide accelerates corrosion and represents a demand on residual free chlorine aside from that of organic matter (39). The identification of safe alternative disinfection methods is therefore desirable.

Silver's antimicrobial effect has been demonstrated in numerous applications against different types of microorganisms (7, 10). The bactericidal efficacy of silver is through its binding to disulfide or sulfhydryl groups in cell wall proteins (11, 35). Silver also binds to DNA (38). Through these binding events, metabolic processes are disrupted, leading to cell death (21).

Silver has been reported to delay or prevent the formation of biofilms in medical catheters (8, 13, 15, 33), prosthetic heart valves (3, 17), vascular grafts, and fracture fixation devices (6, 9). Silver has also been used in water filters (31), cooling towers (22), and DSs (23, 26, 29). Silver exerts its antimicrobial effect by progressive elution from the devices.

Silver is effective against planktonic bacteria (34) and has been used for water disinfection in Europe (18, 31). In addition, silver, in combination with copper, has proven effective against Legionella pneumophila in hospital DSs for more than a decade (37). Silver is not believed to react with most organics in DSs or to produce toxic by-products (46). The objective of this study was to determine if silver inhibits biofilm formation on two very different surfaces to evaluate its potential as a residual disinfectant in DSs.

News from the Market....BED BUGS AGAIN

Bedbugs are small, oval, brownish insects that live on the blood of animals or humans. Adult bedbugs have flat bodies about the size of an apple seed. After feeding, however, their bodies swell and are a reddish color.
Bedbugs do not fly, but they can move quickly over floors, walls, and ceilings. Female bedbugs may lay hundreds of eggs, each of which is about the size of a speck of dust, over a lifetime.
Immature bedbugs, called nymphs, shed their skins five times before reaching maturity and require a meal of blood before each shedding. Under favorable conditions the bugs can develop fully in as little as a month and produce three or more generations per year.
Although they are a nuisance, they do not transmit diseases.

 

Where Bed Bugs Hide

Bedbugs may enter your home undetected through luggage, clothing, used beds and couches, and other items. Their flattened bodies make it possible for them to fit into tiny spaces, about the width of a credit card. Bedbugs do not have nests like ants or bees, but tend to live in groups in hiding places. Their initial hiding places are typically in mattresses, box springs, bed frames, and headboards where they have easy access to people to bite in the night.
Over time, however, they may scatter through the bedroom, moving into any crevice or protected location. They may also spread to nearby rooms or apartments.
Because bedbugs live solely on blood, having them in your home is not a sign of dirtiness. You are as likely to find them in immaculate homes and hotel rooms as in filthy ones.

When Bedbugs Bite

Bedbugs are active mainly at night and usually bite people while they are sleeping. They feed by piercing the skin and withdrawing blood through an elongated beak. The bugs feed from three to 10 minutes to become engorged and then crawl away unnoticed.

Most bedbug bites are painless at first, but later turn into itchy welts. Unlike flea bites that are mainly around the ankles, bedbug bites are on any area of skin exposed while sleeping. Also, the bites do not have a red spot in the center like flea bites do.
People who don't realize they have a bedbug infestation may attribute the itching and welts to other causes, such as mosquitoes. To confirm bedbug bites, you must find and identify the bugs themselves.

Signs of Infestation

If you wake up with itchy areas you didn't have when you went to sleep, you may have bedbugs, particularly if you got a used bed or other used furniture around the time the bites started. Other signs that you have bedbugs include:

• Blood stains on your sheets or pillowcases
• Dark or rusty spots of bedbug excrement on sheets and mattresses, bed clothes, and walls
• Bedbug fecal spots, egg shells, or shed skins in areas where bedbugs hide
• An offensive, musty odor from the bugs' scent glands

WHY DOES BACTERIA AND MOLD PRODUCE BAD ODORS

SEE INTERESTING ARTICLE BELOW:

Q: I am finding that some of my water jobs quickly get a musty odor, much like a moldy smell, even when I arrive the same day the loss occurs. Why can I smell mold that quickly?

 

A: Actually, mold growth does not begin to become microscopically detectable until eight to 10 days after the water incursion, and is not visible until 18 to 20 days.

 

For more information on this, before we get into this particular discussion about the cause of some of these odors you are encountering, please see the article in the May issue of Cleanfax magazine for the peer reviewed scientific documentation.

 

As a water damage technician, we show up at a water job and there is that tell-tale musty, moldy odor. We may even start the drying process when there is no odor, and the next day that musty odor has appeared.

 

What is causing this odor? If the odor is not caused by mold, then what is causing it? The answer is probably bacteria.

 

It is true that the odor could be from old mold. Assuming a normal response time to a water loss of 12 to 24 hours, then for the odor to be coming from mold would mean that the mold was already there before the water loss — thus a pre-existing condition. So if mold is not visible, the source of the odor is probably bacteria.

 

Bacteria basics

 

Before getting into what to do about the bacteria that is causing the odor at the water loss, we need to understand what bacteria are, and if they pose a health hazard.

 

According to paleontologists, who are scientists that study the history of life on Earth, bacteria were the first life form to develop on Earth.

 

Bacteria have the largest numbers of any life form on earth. It is estimated that there are 5 x 10 to the 30th power of bacteria on Earth (this number is a 5 followed by 30 zeros).(1)

 

The microbiologists who study bacteria estimate that there are 10,000,000 species on earth, with only about 9,000 having been identified. In comparison, there are about 5,500 identified species of mammals on earth.

 

Bacteria live everywhere on Earth, and live on everything on earth. Actually "cataloging" all bacterial life will probably never be accomplished. If you went into your back yard and took a shovel of dirt, in that shovel would be an estimated 2.2 million bacteria.(1)

 

Looking at bacteria from a different perspective, a weight perspective, here are some interesting statistics:

 

There are about 6.8 billion humans on Earth, and if each human weighs an estimated 160 pounds, then the total weight of the human population on earth would be about 1.1 x 1012 pounds, this 1.1 x 10 to the 12th pounds. As an example of how big this number is, if we stacked one dollar bills on top of each other, this amount of 1.1 x 1012 of dollar bills would reach the moon, which is about 240,000 miles from Earth.

The total weight of bacteria on Earth is estimated to weigh 1 x 10 to the 15th pounds.(1)

Thus the total weight of bacteria on Earth is much larger than the weight of all the humans on Earth.

Bacteria have always been here and have always been very abundant.

 

When most of us hear the word bacteria, we have an immediate negative reaction. The word "bacteria" to most of us means sickness, illness and disease, among others. Nothing could be further from the truth. If it was not for bacteria, the human race would not exist. Bacteria are 100 percent essential for us, as humans, to live. A few examples:

 

Bacteria on your skin (2)

1,000 different species

Different species live on different regions of the human body

Many act as defense mechanism against pathogenic bacteria

Bacteria in your mouth (3)

500 to 1,000 different species

Even after brushing and rising with mouthwash, thus killing most bacteria, the bacteria regenerate in about two hours (which is a good thing)

These bacteria are a major bodily defense mechanism

Bacteria in your large intestine (4)

700 different species of bacteria, weighing about 4 pounds

Produce vitamin K, vitamin B, thiamine, riboflavin

Digest fiber.

Bad bacteria

 

While there are thousands of bacteria which live on us, in us, and protect us, there are some "bad" ones.

 

There are hundreds of species of bacteria that can, and do, cause sickness and disease. These are called pathogenic. The ones we hear about most often are the likes of Escherichia coli (E-coli), Salmonella, Shigella, Streptococcus, pneumonia, tuberculosis, cholera, etc.

 

And, we have just seen an apparently new bacteria strain of E-coli in Europe.

 

In most buildings, the common types of bacteria that are present include micrococcus, staphylococcus and bacillus. All of these live on our human skin and are mostly benign.

 

The reason these bacteria are found in buildings is that we, as humans, shed our surface layer of skin and these bacteria are also shed with the dead skin cells. So, while there can be pathogenic bacteria in buildings, they are normally not present.

 

While pathogenic bacteria are cause for concern, they can be destroyed by the proper use of biocides/antimicrobials, or by taking away one of their requirements for life, either their food source or water.

 

Bacteria growth

 

Bacteria are single-celled forms of life that are very small in size, about 0.2 to 1 micrometers in diameter. As a comparison, a human hair is 40 micrometers to 120 micrometers in diameter and photo copy paper is about 100 micrometers.

 

Bacteria reproduce by a process that is called binary fission, which means they split from one cell into two cells. Many species of bacteria can reproduce almost continually.

 

The "splitting" can occur as fast as every 15 minutes, which is much quicker than mold reproduces. While this does not seem very quick, watch the math: (5)

 

Start with one cell, 15 minutes = 2 cells, 30 minutes = 4 cells, 45 minutes = 8 cells, 60 minutes = 16 cells

Four hours after the start = 65,536 cells

Eight hours after the start = 4,294,967,296 cells, almost 4.3 billion cells.

With this reproduction rate, the quantity of bacteria literally explodes. Even if we respond to the water loss eight hours after the event, we are caught behind the curve.

 

The numbers go beyond imagination if you look at 24 hours, since the quantity can keep doubling every 15 minutes.

 

With bacterial growth rates that are exploding at a water loss, they have to obtain energy to survive, grow and continue their reproduction.

 

Bacteria obtain energy from digestion. Bacteria's digestion occurs outside of the organism and one of the by-products of this process is off-gassing, which creates the musty odor that we probably smell at the routine water loss.

 

The odor that becomes noticeable at a water loss can be very similar to odor given by mold. These odors are known as microbiological volatile organic compounds (MVOCs). It is this off-gassing that could be the odor that is present when we arrive and/or could be the odor that appears on day two of the water loss.

 

Many times, you will hear water damage technicians say something like, "I am applying a biocide to stop the odor from showing up on day two."

 

What the technician is, in effect, doing is applying a biocide to kill the bacteria which eliminates the generation of MVOCs.

 

Fighting the bacteria

 

The ways to minimize, reduce or eliminate bacteria are by proper cleaning, drying and the application of biocides.

 

There are many different formulations of effective biocides that are routinely used to kill bacteria on a water loss. Many of these solutions use, as their primary "killing" chemicals, the same chemicals that we find in everyday life. Here are some examples:

 

Hydrogen peroxide used on cuts to kill bacteria

Phenols, which are used in biocides, are also the same used in a popular mouth wash

The orange colored biocide that is used by phlebotomists on your arm before taking blood is iodine, which is known as an iodophor in chemical terms

Quaternary ammonium compounds are used in household cleaners/disinfectants that are used in bathrooms and kitchens

Hypo-chlorites that are in solutions are also used in your clothes washer to clean whites, commonly called bleach.

While there is justifiable concern about misuse of biocides, most of the biocides used in our industry have been around for years and when used properly can kill both bacteria and mold and do not pose a human health risk.

 

"Killing" mold is not an acceptable method of mold remediation, but that is for another article. Killing bacteria with biocides is a very acceptable method of decontamination. It is routinely done in hospitals, doctors/dentists offices, food process facilities, restaurants, etc.

 

Bacteria, like all forms of life on Earth, needs water to live. Below is a table showing different levels of water activity and the type of microbial life each level supports.

 

Water activity is the water that is available to support microbial life at the very surface level of a material, which is the location where we find microbial growth.

 

Water activity and moisture content are somewhat related, but a full discussion is for another article.

 

Water Activity (wetness) - Minimum to support                Life Form Supported

0.95        Bacteria

0.88        Most Fungi

0.66 to 0.70         Mold: Penicillium, Aspergillus

As can be seen from this chart, bacteria need a lot of water to live. In fact, bacteria needs more water to live than does mold. As a comparison, the average human should consume 25 ounces of water per day. Less than this amount may lead to health problems. With water activity, if the amount of water is below the above values, then there is not enough water for microbial life to live.

 

When water is taken away from bacteria, they die; some types of bacteria will generate spores as the living bacteria die. This is different from mold. When water is taken away from mold, mold goes into a state called dormancy. Mold, in effect, goes into a waiting pattern for water to return — it does not die.

 

Thus, drying can be an effective bacterial killing method.

 

Musty odors

 

Back to our tell-tale odor at the water loss. That musty odor can be a sign of mold growth, which may not be visible. Mold can be living and growing inside wall cavities, under cabinets, under carpet/pad and in other "hidden" locations.

 

However, the odor you encounter is more likely caused by bacteria that are ever-present in homes and grow very rapidly when exposed to water.

 

If you find mold right after a water loss, it is most likely pre-existing, and not from the immediate water loss.

 

The best method to reduce bacteria and their odors and potential negative health impacts is by:

 

Properly cleaning the affected areas

Drying the structure

Appropriate use of biocides.

If a structure is clean and dry, then there cannot be any microbial life.

 

References:

 

(1)          Whitman, W. B., Coleman, D. C., Wiebe, W. J. "Prokaryotes:

      The unseen majority." National academy of Sciences, pp 6578

      – 6583. June 1998, University of Georgia, Athens, GA

 

(2)          Todar K. Normal Bacterial Flora of Humans Todar's Online

      Textbook of Bacteriology

 

(3)          Zimmer, Carl. "How Microbes Define and Defend Us." Science,

      New York Times. 12 July 2010

 

(4)          Maton, Anthea; Jean Hopkins, Charles William McLaughlin, Susan

      Johnsons, Maryanna Quon Warner, David LaHart, Jill D. Wright

      (1993). Human Biology and Health. Englewood Cliffs, New Jersey,

      USA: Prentice Hall

 

(5)          Zwietering M H, Jongenburger I, Rombouts F M, van 'T Riet K

      (1990). "Modeling of the Bacterial Growth Curve". Applied and

      Environmental Microbiology 56 (6): 1875–1881

 

Richard Driscoll has a B.S. degree in mechanical engineering from Clarkson College of Technology, an MBA from the University of Dayton and is currently working on his doctorate. He is a professor at Webster University, where he provides graduate and under-graduate level lectures on marketing, international business management and business metrics. He is an Institute of Inspection, Cleaning and Restoration Certification (IICRC) Certified Master Restorer and an approved instructor. Driscoll has been consulted by state governments on legislation related to the cleaning and restoration industry. He also is the author and instructor for Restoration Sciences Academy's MR-110 and MR-210 microbial remediation classes. He can be reached at Richard@mayhemmishaps.com.