Facts At Your Fingertips

April 1, 2013

Gas Hazard Definitions and Data

The detection of gases in plant environments has a critical and wide-ranging role in the chemical process industries (CPI). Among the major applications of gas detection are limiting personnel exposure to hazardous chemicals, preventing explosive atmospheres, protecting the environment and identifying leaks in process equipment. Table 1 summarizes the main reasons for gas monitoring.

All CPI workers should be conversant with gas-detection terms to promote safety, health and environmental quality. The following is a collection of terms and data involving hazardous gases (Table 2).
PEL (permissible exposure limit). Set by OSHA to limit workers’ exposure to an airborne substance, PELs are based on an eight-hour time-weighted average. PELs are enforceable legal limits.
TLV (threshold limit value). Established by the American Conference of Governmental Industrial Hygienists, TLVs are based on known toxicity of chemicals in humans or animals, and are recommendations, rather than legal limits.
IDLH (immediately dangerous to life and health). Defined in the U.S. by the National Institute for Industrial Safety and Health (Part of the Centers for Disease Control and Prevention) as a level of exposure that is likely to cause death or immediate or delayed permanent adverse health effects
LC₅₀ (median lethal concentration). A measure of the toxicity of a surrounding medium that will kill half of a sample population of test animals in a specified period through exposure via inhalation.

Oxygen deficiency

Normal ambient air contains 20.8 vol.% oxygen. When oxygen concentration dips below 19.5 vol.% of the total atmosphere, the area is considered oxygen deficient. Oxygen deficiency may result from O₂ being displaced by other gases, such as carbon dioxide, and can also be caused by rust, corrosion, fermentation or other forms of oxidation that consume oxygen. Table 3 outlines the physiological effects of oxygen deficiency by concentration.
If oxygen concentrations in the air rise above 20.8%, the atmosphere is said to be oxygen-enriched. Higher oxygen levels can increase the likelihood and severity of a flash fire or explosion, because the oxygen-enriched atmosphere tends to be less stable than air.

Table 1. summary of the main reasons for gas monitoring.
Type of monitoring	Purpose	Hazard	Possible source of hazard
Personal protection	Worker safety	Toxic gases	Leaks, fugitive emissions, industrial process defects
Explosive	Worker safety and facility safety	Explosions	Presence of combustible gases and vapors due to leaks or process defects
Environmental	Environmental safety	Environmental degradation	Acid gas emissions
Industrial process	Process control	Process malfunction	Process errors
Source: MSA

Table 2. Exposure data for selected hazardous gases
Chemical and formula	Properties	OSHA PEL (ppm)	IDLH (ppm)	LC50 (ppm)
Ammonia (NH3)	Corrosive, flammable	50	300	4,000
Boron trifluoride (BF3)	Toxic	1	25	806
Bromine (Br2)	Highly toxic, corrosive, oxidizer	0.1	3	113
Carbon monoxide (CO)	flammable	50	1,200	3,760
Carbon dioxide (CO2)		5,000	40,000	Not available
Chlorine (Cl2)	Toxic, corrosive, oxidizer	1	10	293
Chlorine dioxide (ClO2)	Toxic, oxidizer	0.1	5	250
Ethylene oxide (C2H4O)	Flammable	1	800	4,350
Hydrogen chloride (HCl)	corrosive	5	50	2,810
Hydrogen sulfide (H2S)	Toxic, flammable	20	100	712
Methyl isocyanate (CH3NCO)	Highly toxic, flammable	0.02	3	22
Nitrogen dioxide (NO2)	Highly toxic, oxidizer	5	20	115
Phosphine (PH3)	Highly toxic, pyrophoric	0.3	50	20
Sulfur dioxide (SO2)	Corrosive	5	100	2,520

Table 3. Physiological effects of oxygen deficiency by degree
Concentration of O2 in atmosphere, vol. %	Physiological effect
19.5 to 16	No visible effect
16 to 12	Increased breathing rate; accelerated heartbeat; Impaired attention, thinking and coordination
14 to 10	Faulty judgment and poor muscular coordination; Muscular exertion, causing rapid fatigue; Intermittent respiration
10 to 6	Nausea and vomiting; Inability to perform vigorous movement or loss of the ability to move; Unconsciousness, followed by death
Below 6	Difficulty breathing; convulsive movements; death in minutes
Source: MSA

Combustible atmospheres

Vapor and gas. Although these two terms are sometimes used interchangeably, they are not identical. Vapor refers to a substance that, though present in the gaseous phase, generally exists as a liquid or solid at ambient temperatures. Gas refers to a substance that generally exists as a gas at room temperature.
Vapor pressure and boiling point. Vapor pressure can be defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed or solid form. Vapor pressure is directly related to temperature, and along with boiling point, determines how much of a chemical is likely to become airborne. Substances with low vapor pressures generally present less of a hazard because there are fewer molecules of the substance to ignite, but they may require higher-sensitivity instrumentation to detect.
Vapor density. Vapor density is the weight ratio of a volume of vapor compared to an equal volume of air. Most flammable vapors are heavier than air, so they may settle in low areas.
Explosive limits. To produce a flame, a sufficient amount of gas or vapor must exist. But too much gas can displace the oxygen in an area, making it unable to support combustion. Therefore, there is a window of concentrations for flammable gas concentrations where combustion can occur. The lower explosive limit (LEL) indicates the lowest quantity of gas required for combustion, while the upper explosive limit (UEL) indicates the maximum quantity of gas (Table 4). Gas LELs and UELs can be found in NFPA 325. LELs are typically 1.4 to 5 vol.%. As temperature increases, less energy is required to ignite a fire and the percent gas by volume required to reach the LEL decreases, increasing the hazard. An environment with enriched oxygen levels raises the UEL of a gas, and the rate of flame propagation. Mixtures of multiple gases add complexity, so their exact LEL must be determined by testing.

References

1. U.S. Dept. of Labor, Occupational Safety & Health Administration (OSHA), 29 CFR 1910.1000 Table Z-1.

2. U.S. Centers for Disease Control and Prevention. National Institute for Occupational Safety and Health (NIOSH). NIOSH Pocket Guide to Chemical Hazards. www.cdc.gov/niosh/npg. Accessed March 2013.

3. Mine Safety Appliances Co., “Gas Detection Handbook” 5th ed. MSA Instrument Div., August 2007.

4. National Fire Protection Association. NFPA 325: Guide to Fire Hazard Properties of Flammable Liquids, Gases and Volatile Solids, 1994.

THE DIFFICULT "Clostridium difficile"

What Is C. diff?

In 2009, officials at Jewish Hospital-Mercy Health knew they had a problem — its Clostridium difficile (C. diff) incidence rate had hit an all-time high of 25.27 per 10,000 patients and they didn’t know why.

“We had to do something,” says Jenny Martin, manager of quality administration. 

The Cincinnati hospital convened a task force of clinical services professionals, physicians, nurses, administrators and environmental service workers to assess the spike in infections caused by this deadly bacterium, which ravages the intestines. They found that the patient makeup of the 209-bed hospital was partly to blame. C. diff is a bacterium that preys on the sick, particularly those who are elderly or immunocompromised — both of which Jewish Hospital-Mercy Health had plenty of.

“We have an older patient population — the average patient age is 72 years old — and we have a blood and bone marrow transplant center,” Martin says. “The type of antibiotics we use makes these patient populations very susceptible to C. diff infections.” 

Hospital officials acted quickly and were able to slash the facility’s high C. diff rate by 50 percent in six months by standardizing care, adopting stricter antibiotic controls and incorporating new room-cleaning protocols. 

“But in all honesty, the changes to our environmental cleaning practices had the most significant impact out of all of the changes we made,” says Martin. 
As this example shows, when it comes to hospital-acquired infections custodial cleaning practices can make a world of difference. 

About 50 percent of the population naturally carries clostridium difficile (C. diff) in their intestines, states Benjamin Tanner, president of Antimicrobial Test Laboratories, Round Rock, Texas. 

“It lives in harmony with the other bacteria in your intestines and doesn’t cause problems,” he says. “The only time it makes individual’s ill is when people go on multiple or individual antibiotic therapy.”

The bacteria, C. diff, exists within the body in a vegetative state and doesn’t make people sick, unless illness, disease and antibiotic use puts them at risk, Tanner explains. At that point, C. diff mutates into its active state, forming a resistant end spore that becomes difficult, if not impossible, to eradicate from the environment. 

“These spores are exceedingly difficult and challenging to disinfect,” says Tanner. “Once they enter the environment, there are only a few disinfectants and technology that can kill it. The spores tend to get everywhere. They move easily from surface to surface.”
While antibiotics cannot always treat these infections, good cleaning and hygiene can prevent them from spreading. It’s safe to say when it comes to C. diff the best offense is a good defense. 

Cleaning with bleach is the No. 1 means of attacking C. diff spores, say experts. 

“There are probably only four to five EPA-registered bleach-based disinfectants with a C. diff claim. These have passed laboratory testing showing they can kill millions of C. diff spores on a surface,” says Tanner. “They are currently the best way to clean C. diff from a surface.”

Darrel Hicks, director of environmental services and patient transportation at St. Luke’s Hospital in St. Louis, and author of “Infection Control For Dummies,” agrees that the best disinfectants used in a C. diff situation are bleach based.

“The spore is very difficult to break through and conventional disinfectants won’t do it. You have to use a sporicidal disinfectant,” he says. “Though bleach can be highly corrosive to surfaces, it is effective against C. diff and our goal is to help save people’s lives.”

As an alternative to bleach, some facilities are experiencing success in the fight against C. diff  by using accelerated hydrogen peroxide (AHP) products. These are clear, colorless and odorless products that are less harsh than bleach counterparts.

Composed of hydrogen peroxide, surface acting agents (surfactants), wetting agents (allows liquid to spread easier) and chelating agents (helps to reduce metal content and/or hardness of water), AHPs have proved successful in killing C. diff spores. In fact, according to testing done by “American Journal of Infection Control,” when used as directed, AHP proves to be as effective as bleach.

No matter which disinfectant is used against C. diff, Tanner advises paying critical attention to dwell times in patient rooms. 

“There’s a linear relationship between how long a disinfectant remains wet on a surface and how much disinfection you get,” he says. “You can take a great disinfectant, such as bleach, and if you only leave it on a surface for five seconds, you won’t get nearly the effect you need. Contact time is critical for a liquid disinfectant. If you don’t use it long enough, you won’t get the same level of disinfection.”

At St. Luke’s Hospital, Hick’s staff cleans C. diff patient rooms twice daily. Housekeepers perform thorough cleaning once a day, and then come back a second time to cleanse all high-touch surfaces in the room. 

“We go over these surfaces with bleach wipes,” Hicks says. “We go after the spores on a daily basis rather than just on discharge like a lot of hospitals do.”

Taken from CleanLink ,April 2013

TRIBUTE TO RUST

March 1, 2013

By Kristin Johansson,  PCI Magazine

I recently came across an inspiring story from Harley-Davidson® regarding a highly corroded motorcycle. This particular motorcycle, a 2004 FXSTB Softail Night Train, drifted for more than a year across the Pacific Ocean following the tsunami that devastated parts of northern Japan in 2011. The motorcycle was recovered off the coast of British Columbia by a man named Peter Mark, when it washed ashore at low tide. He discovered the motorcycle, still bearing its Japanese license plate, in a container where the bike was being stored by its owner.

Mark worked with news agencies and representatives from Deeley Harley-Davidson Canada and Harley-Davidson Japan, and eventually found the owner, Ikuo Yokoyama, who lost his home and members of his family in the tsunami. Still struggling to rebuild his life in the aftermath of the disaster, Yokoyama declined Harley-Davidson’s offer to restore and return the bike to him, although he was grateful for the offer and touched by the outpouring of support from Harley riders around the world. He asked to have the motorcycle preserved in its current condition and displayed at the Harley-Davidson Museum as a memorial to those whose lives were lost or forever changed on that day. The bike is now under glass in the Harley-Davidson museum in Milwaukee. As per Yokoyama’s request, it remains un-restored and largely untouched.

In this situation the corrosion is a tribute for all to see. However, corrosion is normally a widespread, costly and hazardous problem that no one wants to see. The American Galvanizers Association estimates that metallic corrosion costs nearly $423 billion annually in the United States, and about one third of that is noted as avoidable corrosion – a cost that could be eliminated if proper corrosion protection methods were in place.