Exposure limits definitions

Table 2-4 lists the parameters used to monitor radiation as well as some of the exposure limits. Definitions of terms are in the Glossary. Recommended practice for fire protection is in NFPA 801. 

Finally, STEL (short term exposure limit) corresponding to the definition of LVE and TLV/TWA (direshold limit value/time weight average) are the equivalent of the French MVE. There are sometimes differences in values between STEL and LVE on the one hand, and TWA and MVE on the other hand. 

Numerous case reports are available regarding the lethal and nonlethal toxicity of arsine in humans, but definitive exposure concentration or duration data are lacking. Although the case reports are of limited use for quantitative estimates of exposure limits, they do provide qualitative information about the nature of arsine poisoning in humans. Some estimated human toxicity values are available and are summarized in Table 2-3. 

These two definitions reflect two sides of the same situation. In this book, the term critical effect(s) will be used for the hazard/effect considered as being the essential one(s) for the purpose of the risk characterization, e.g., for the establishment of a health-based guidance value, permissible exposure level, or Reference Dose. It should be noted that the critical effect could be a local as well as a systemic effect. It should also be recognized that the critical effect for the establishment of a tolerable exposure level is not necessarily the most severe effect of the chemical substance. For example, although a substance may cause a serious effect such as liver necrosis, the critical effect for the establishment of, e.g., an occupational exposure limit could be a less serious effect such as respiratory tract irritation, because the irritation occurs at a lower exposure level. 

TLV The TLV or Threshold Limit Value refers to a safe level of exposure by inhalation. The definition was established by the American Conference of Governmental Hygienists. There are several variations or criteria levels for the TLV. As an example, hydrogen sulfide has a TLV for short-term exposure limits (STEL) of 15 minutes of only 5 ppm. Comparing this to the TLV-STEL of 400 ppm for carbon monoxide provides an indication of the need to be extremely careful when H2S is suspected. Under OSHA Standards, and particularly on MSDS (Material Safety Data Sheets) compounds are associated with a time weighted average (TWA) TLV, which is the allowable concentration for an 8-hour continuous exposure period. For firefighting purposes, the short-term exposure is likely more realistic. 

There is no clear definition for the terms safe exposure limit (SEE) and occupational exposure limit (OEL), although the terms has scientific and legal interpretations and implications. The values of SEE or OEE vary from country to country around the world. It is well known that a rough rule of thumb is that the SEEs and OEEs are levels below which most industrial workers and the general population could get exposed to chemical substances on a regular basis with a low risk to health. It should be clearly understood that SEE and OEE are certainly not levels that are definitely safe and below which no harm is caused. 

Exposure conditions -H Realistic concentrations -H Real chemical interactions - Definition of exposure difficult - Confounding agents interfere -H Well-defined exposures - Limited to low concentrations -H Well-defined exposures -H Wide concentration range possible + Easy exposure manipulation... 

The guideline contains extensive lists of solvents of all three classes, with limits for each. Known toxicology data are given for each solvent, with definitions for parameters and methods of establishing exposure limits such as permitted daily exposure (PDE), no-observed-effect level (NOEL), lowest-observed-effect level (LOEL), tolerable daily intake (TDI), and acceptable daily intake (ADI). 

Occupational exposure limits for airborne concentrations of hazardous substances are essentially measurable values of airborne (and therefore breathable) contmnination by chemical substances that are points of reference for the development of workplace strategies to protect workers from health risks associated with inhalation of chemical substances. Beyond this general definition lie a number of levels of complexity and contradiction. 

As we outlined in Chzpter 3, under Act 1568/85 (Chapter V, Article 24, Definitions) there were two types of exposure limit defined, Exposure limit values (OELs) and biological indicator limit valu. Subsequently Presidential Decree (P.D) 338 001 transcribed almost verbatim flie Dir tive 98/94/EC on the protection of the health and safety firom the risks related to chemical agente at work . It redefined exposure limit values as follows ... 

They go on to state that it is therefore important to seek to keep exposure to the lowest levels possible and that the OEL is not regarded as an end in itself but rather as an indication of what is definitely unacceptable. Tho-efore the employer is required to keep exposures to as far below the exposure limit as possible. According to this provision, theoretically, the Labour In ectorate can enforce measures against an employer even if the limit is not exceeded. 

Aside from the definitions presented above, section I of directive 98/24/EC contains basic principles on the procedure for establishing of occupational exposure limits on the European Community level. The following types of limits have to be distinguished ... 

For some chemicals, the material safety data sheet Material Safety Data Sheet (MSDS) show a short-term exposure limit (STEL) value. STEL is defined as the 15-minute average that should not be exceeded even if the average value for an eight-hour day is below the PEL. STEL values are related to short term effects while PEL values apply to chronic exposures. The following are some definitions used by OSHA ... 

The TLV is one of various indices of permissible exposure levels to chemicals another is the Short Term Exposure Limit (STEL), which represents a 15-minute concentration which should not be exceeded in an 8-hour workday. Its aim is particularly to prevent the acute effects of short-term exposure. STEL values can be found, along with a more precise definition, in Threshold Limit Values, published by the ACGIH (Cincinnati, USA). 

There are numerous limiting values set to protect employees against workplace exposures. The definitions of these values are given below ... 

Br = 450mT and power density Sr = 50 W.m . Their definition allows fast decision on not exceeding the exposure limit values and on risk acceptability without demanding calculations and measurements. 

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