IDLH Level

Toxicity together with the volatility of a compound dictates the effectiveness of a CWA or TIC when deployed. Common terms used to gauge the relative toxicity of a CWA or a TIC are IDLH level, LQ50, ICtso, TWA (time-weight average), and 

IDLH level is the concentration of a chemical in the air that would cause immediate or delayed permanent adverse heath effects after 30 min of unprotected exposure. At IDLH level, an exposed person may have 30 min to escape the contaminated environment without loss of life or irreversible health effects. The IDLH 

The purpose for estabhshing the IDLH level is to determine a concentration that permits sufficient time for a person to escape safely or to seek protection without incurring serious injury or irreversible health effects. In determining IDLH levels, the ability of a person to escape or seek protection was considered together with severe eye or respiratory irritation and other deleterious effects (e.g., disorientation or lack of coordination) that could prevent a timely escape. The IDLH level is the concentration at which the dosage received during a 30-min exposure without physical protection would cause minimal adverse health effects. However, the 30-min period is not meant to imply that people should stay in that contaminated environment any longer than necessary. In fact, every effort should be made to evacuate the locale immediately. 

IDLH levels vary widely among diverse compounds. A lower value means that the compound is more dangerous and has greater toxicological effects. The volatility of all CWAs and most TICs is, unfortunately, much higher than respective determined IDLH level. This means that the vapor concentration in the air can easily reach the dangerous level. 

The establishment of IDLH levels does not mean that exposure to lower levels of CWAs or most TICs is safe. Exposure to chemicals at concentrations much lower than the IDLH level for a long period will also be dangerous or even fatal. Although exposures to lower concentrations for a short period may not cause immediately observable effects or symptoms, toxicity effects may be cumulative. While some toxic substances (such as HCN) can be gradually detoxified naturally by human organs, many of them cause irreversible effects. The latter type of compound is commonly called refractory. Soman (or GD) and other refractory compounds must be handled with special care to avoid any exposure. 

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Class B—Non-IDLH based on oxygen level between 19.5 and 21 percent, but classified as dangerous due to the airborne presence of toxic or poisonous substance Below IDLH level, but greater than the protection factor offered by air-purifying respirators. 

The Immediately Danger to Life or Health (IDLH) level for CO2, set by the National Institute for Occupational Safety and Health (NIOSH) is 50,000 ppm. At that level, vomiting, dizziness, disorientation, and breathing difficulties occur ifler a 30-minute exposure at a 100,000 ppm, death can occur after a few minutes, even if the oxygen in the atmosphere would otherwise support life. 

The IDLH level is 5.0% and the lethal level is 10.0%. Therefore, the level in the room of 9.05% does e.vceed the IDLH level for CO2. It is also dangerously close to the lethal level. The person e.xtinguishing the fire is in great danger and should take appropriate safety measures. 

Immediately dangerous to life or health (IDLH) levels are 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 respiratory protection should be considered. 

IDLH data are currently available for 380 materials. Because IDLH values were developed to protect healthy worker populations, they must be adjusted for sensitive populations, such as older, disabled, or ill populations. For flammable vapors the IDLH concentration is defined as one-tenth of the lower flammability limit (LFL) concentration. Also note that IDLH levels have not been peer-reviewed and that no substantive documentation for the values exists. 

SPEGLs or EEGLs are available, IDLH levels provide alternative criteria. However, because IDLH levels were not developed to account for sensitive populations and because they were based on a maximum 30-min exposure period, the EPA suggests that the identification of an effect zone should be based on exposure levels of one-tenth the IDLH level. For example, the IDLH level for chlorine dioxide is 5 ppm. Effect zones resulting from the release of this gas are defined as any zone in which the concentration of chlorine dioxide is estimated to exceed 0.5 ppm. Of course, the approach is conservative and gives unrealistic results a more realistic approach is to use a constant-dose assumption for releases less than 30 min using the IDLH level. 

Immediately Dangerous to Life or Health (IDLH) According to NIOSH (1997), the IDLH level .. . for the purpose of respirator selection represents a maximum concentration from which, in the event of respirator failure, one could escape within 30 minutes without experiencing any escapeimpairing or irreversible health effects. Concentrations are typically reported in parts per million (ppm) or milligrams per cubic meter (mg/m ). 

National Institute for Occupation Safety and Health Administration (NIOSH), immediately dangerous to life or health (IDLH) levels. 

NIOSH defines IDLH levels as the maximum airborne contaminant concentration from which one could escape within 30 minutes without any escapeimpairing symptoms or any irreversible health effects. Since, IDLH levels are only intended for emergency situations, their concentration for a particular chemical is considerably higher than OSHA and ACGIH values. 

The Occupational Safety and Health Administration permissible exposure limit is 3 ppm (lOmgm ) as an 8h, time-weighted average. The American Conference of Governmental Industrial Hygienists and National Institute for Occupational Safety and Health recommend 3 ppm as a ceiling concentration. The Revised (1996) IDLH level is 30 ppm. The temporary emergency exposure limits (TEELs) are TEEL-0, TEEL-I, and TEEL-2 (pgm ) 10000 TEEL-3 (pgm ) 100 000. 

As described earlier, the immediately dangerous to life and health (IDLH) level is the maximum concentration of a substance to which one can be exposed for 30 min without irreversible health effects or death. A lethal level is the concentration at which death is almost certain to occur. The IDLH values were determined by the National Institute for Occupational Safety and Health (NIOSH) for the purpose of respirator selection. Respirators provide protection against the inhalation of toxic or harmful materials and may he necessary in certain hazardous situations. 

Calculate how many milliliters of each chemical would have to evaporate in order to reach the TLV concentration and how much would have to evaporate to reach the IDLH level. 

Although the time to reach the IDLH levels of pyridine, -hexane, and methyl acrylate are substantially longer than bromine, the time to reach the TLV of all of these chemicals in the unventilated laboratory is only a few minutes. For each of these chemicals, the concentration in the laboratory could be kept below the TLV with reasonable air flowrates, even when increased by an appropriate safety factor. A spill or routine repeated use of these chemicals in an unventilated laboratory would definitely result in a significant health risk and should be avoided. If a large safety factor is necessary, requiring air flowrates that are impractical, other measures to reduce the concentration in the air, such as localized hoods, should be considered. 

Human toxicity data for these agents has not been published or has not been established. However, the industrial IDLH levels for these agents are as low as 2 ppms. 

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