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U.S. Department of Labor | |
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| Occupational Safety & Health Administration | ||||||
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Introduction Nerve agents consist of a group of very toxic organophosphate chemicals specifically designed for military warfare. These include the agents code-named GA (Tabun), GB (Sarin), GD (Soman), Cyclohexyl Sarin (GF), and VX. Other organophosphate chemicals include commercial insecticides such as Malathion®. These chemicals all cause similar effects on the human body by disrupting how nerves communicate and control muscles, glands, and organs. Though they cause similar effects, nerve agents are more toxic than commercial insecticides -- so smaller amounts can cause effects of concern. Most of the nerve agents exist as liquids but some (such as GB) volatilize into the air on their own. VX is the least likely to become airborne, but in conditions involving explosions, it could vaporize and spread in the air. Personal Protective Equipment The recommendations for personal protective equipment (PPE) should be based on a site-based job hazard analysis of possible hazards including skin contact, air concentrations, heat stress, etc. All PPE should be used with appropriate additional administrative controls including medical surveillance, employee training, respirator fit-testing, and decontamination procedures to limit the potential for unforeseen adverse effects. There are no current OSHA Permissible Exposure Limits (PELs) for exposure to nerve agents. The National Research Council and EPA have published airborne limits to various agents called Acute Exposure Guideline Levels (AEGLs) to characterize the risk to the general population during a one-time accident and emergency scenario with time limits not to exceed 8 hours of exposure. For emergency responders and support personnel to a nerve agent event, it seems appropriate to establish a target exposure limit at time weighted averages less than the lowest recommended AEGL-1 level for a given exposure duration. The AEGL-1 tier is the mildest effect category above which the general population, including susceptible individuals, could experience noticeable eye discomfort, irritation, or non-sensory effects. However, the effects are not disabling and are reversible upon cessation of exposure. The AEGL-1 and AEGL-2 values are based upon direct vapor exposure to the human eye and tissues surround the eye (conjunctiva), which are considered the most sensitive organ/tissue for blister agent vapor exposure effects by the National Research Council and the National Academy of Sciences. The CDC has made recommendations for worker exposure limits [35 KB PDF, 5 pages] dealing with routine work processes such as demilitarization and transportation. Note: The CDC/NCEH worker exposure limits do not specifically include storage. These exposure standards may be substituted for work extending beyond the 8-hour AEGL limit if deemed appropriate after an incident. The PPE ensemble selected depends on the level of knowledge available regarding the chemical agent. Respirators chosen initially for responders into a known release area should be a positive pressure self-contained breathing apparatus (SCBA) with a Level A protective suit until monitoring results allow for other decisions. OSHA would generally require these respirators to be NIOSH-certified CBRN SCBA respirators for use by employees. Some chemical warfare agents have been shown to seriously degrade and damage some respirators. Respiratory protection specifically approved by NIOSH for CBRN exposures is highly desirable but where not available, the incident commander may allow alternative suitable respirators during emergency operations. These are, depending on exposure levels, other NIOSH approved SCBAs or full-face air purifying respirators, which have been specifically tested by the manufacturer as effective against chemical warfare agents. Respirators other than SCBAs may be selected based upon accurate monitoring results with appropriate limits of detection for the subject agent. When conditions have been determined to be appropriate for the use of air purifying respirators, a NIOSH-approved CBRN APR Full Facepiece Air Purifying Respirator (APR) with a CBRN Canister, or a Chemical Warfare Agents (CWA) tested full facepiece APR with a combination organic vapor/acid gas/particulate canister may be used. A list of CBRN approved SCBA and APR may be obtained from the NIOSH website - APR or SCBA. The tables below consolidate some information provided by other agencies relating to toxicity, exposure, and the relative protection provided by certain types of respirators and clothing. These limits are for planning purposes and are not recommendations for particular work schedules. Any work schedules should be reviewed by a competent occupational health professional skilled in use of exposure limits and PPE. Respiratory protection and other PPE recommendations are presented in the table below as time-dependent exposure limits by multiplying the NIOSH current assigned protection factor (APF) of the type of respirator and the AEGL-1 target level. Exposures above the limit require a more protective respirator. It should be noted that OSHA's proposed rule on APFs indicate that some hooded or helmeted powered air-purifying respirators have much higher protection factors than the current APF of 25. However, this rulemaking is pending and subject to change. The US Army's Immediately Dangerous to Life or Health (IDLH) level is set as the ceiling limit for respirators other than SCBAs. Any exposures approaching the IDLH level should be regarded with extreme caution and the use of SCBAs for protection should be considered. All air purifying respirators require a change schedule for cartridges or canisters not to exceed the maximum eight hour exposure covered by the AEGLs. A recent estimation of percutaneous absorption of nerve agent vapor suggests that a hazardous dose from skin absorption through airborne exposures is unlikely unless levels are significantly greater than the IDLH levels listed below. Skin protection at lower levels should be designed to prevent skin contact with liquid or contaminated surfaces. Nerve agents are toxic in small amounts on the skin and some can persist in the environment for days.
a) Memorandum Subject: Implementation Guidance Policy for New Airborne Exposure Limits for GB, GA, GD, GF, VX, H, HD, and HT. Department of the Army OASA (I&E), (2004, June 18). b) Final Recommendations for Protecting Human Health from Potential Adverse Effects of Exposure to Agents GA, GB, and VX. Department of Health and Human Services (DHHS), Centers for Disease Control and Prevention (CDC) Federal Register, Vol. 68, No. 196, pp. 58348-58351, (2003, October 9). Also available as a 149 KB PDF, 4 pages. c) Memorandum Subject: Nerve Agent Percutaneous Exposure Criteria and Airborne Exposure Levels (AELs) for GD, GF in Use of Interim DA Guidance on Implementation of the New AELs. Department of the Army Office of the Surgeon General (2004, June 29). Specific Hazard Information Related Online Resources Accessibility Assistance: Contact the OSHA Directorate of Science, Technology and Medicine at 202-693-2300 for assistance accessing PDF materials. |
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