Occupational exposure limit defined

Occupational exposure is defined as chronic exposure in amounts less than the threshold limit value causing material symptoms. As with many teratogens, critical... 

The TL and MAK values should be used as guides in the control of health hazards. They are not constants that can be used to draw fine fines between safe and dangerous concentrations. Nor is it possible to calculate the TL or MAK values of solvent mixtures from the data in Table A-13, because antagonistic action or potentiation may occur with some combinations. It should be noted that occupational exposure limits such as the TL and MAK values are not intended for use as a comparative measure of one solvent against another. The values set airborne concentration limits on chemical exposure, but do not describe the ease with which that airborne limit is achieved. In addition, the vapour pressure of the solvent must also be considered. The lower the vapour pressure, the lower the airborne concentration. In order to better compare the safety of volatile compounds such as organic solvents, the use of the vapour hazard ratio ( VHR) has been recommended as a feasible measure [175], The vapour hazard ratio is defined as the quotient of the saturation concentration of a solvent (in mg/m at a given temperature and pressure) and its occupational exposure limit (in mg/m e.g. TL or MAK values), according to ... 

The initial process in the application of toxicity (dose-response) data in risk assessment is the extrapolation of findings to establish acceptable levels (AL) of human exposure. These levels may be reference values (inhalation reference concentrations, RfC or oral reference doses, RfD), minimal risk levels (MRL) values, occupational exposure limits, and so on. When the toxicity data are derived from animals, the lowest dose representing the NOAEL (preferably) or the LOAEL defines the point of departure (POD). In setting human RfD, RfC, or MRL values, the POD requires several extrapolations (see [13] and revisions). Extrapolations are often made for interspecies differences, intraspecies variability, duration of exposure, and effect level. Each area is generally addressed by applying a respective uncertainty factor having a default value of 10 their multiplicative value is called the composite uncertainty factor (UF). The UF is mathematically combined with the dose at the POD to determine the reference value ... 

Although the EU has been attempting for some years to introduce a system of occupational exposure limits, its current status remains somewhat embryonic and ill-defined. A clear strategy and set of principles for dealing with substances producing respiratory hypersensitivity have not yet emerged. 

For more or less all non-genotoxic carcinogens, a threshold limit value exists where there is no real risk of cancer. Taking this into account, some scientific associations have defined additional categories of carcinogenic substances which have no real carcinogenic potential below their occupational exposure limit. Well-known examples of such substances include sulfuric acid aerosols, hexachloro-benzene, trichloromethane, tetrachloromethane, lindane, dioxane, and 2,3,7,8-tet-rachlorodibenzodioxin (TCDD). 

In addition to the above-mentioned occupational exposure limits, action levels have been defined according to article 2, which are 40 pg m" lead in the air and/ or 40 pg/100 ml blood. If one or both of these levels is exceeded, the following actions have to be taken by the employer according to article 11, as well as informing workers and their representatives ... 

In the past, the HSE has incorporated the American TLV system in a Guidance Note which was published annually. This practice continued until 1984 when a UK system of limits was adopted. Since that time, there have been several types of UK occupational air quality standards including the two-tier Control and Recommended Limit and, until recently, the Maximum Exposure Limit and Occupational Exposure Limit. Both these two-tiered systems defined exposure standards with different requirements for legal compliance. These systems have now been abolished and replaced by the current single-tier Workplace Exposure Limit (WEL) system. The WeL system now forms part of the requirements for adequate control of exposure by inhalation under the COSHH Regulations 2002 (as amended) . 

The degree of protection required will be the factor by which it is necessary to reduce the airborne concentration of the contaminant in order to limit the exposure to below the occupational exposure limit. A fraction of the OEL, i.e. one-tenth, is usually chosen as a suitable level of protection. The degree of protection provided by a specified piece of RPE is given by a designated nominal protection factor (NPF), which is defined as the ratio of the concentration of contaminant present in the ambient atmosphere to the calculated concentration in the breathing zone when the RPE is being worn. 

TWA An abbreviation for time weightedaverage, it is an occupational exposure limit used to protect the health of employees against exposure to harmful aiibome substances. It is averaged over a defined period of time to which workers maybe exposed by inhalation. See... 

Inhalation. The threshold limit value of HCN is 4.7 ppm. This is defined as the maximum average safe exposure limit for a 15-min period by the Occupational Safety and Health Administration. Exposure to 20 ppm of HCN in air causes slight warning symptoms after several hours 50 ppm causes disturbances within an hour 100 ppm is dangerous for exposures of 30 to 60 min and 300 ppm can be rapidly fatal unless prompt, effective first aid is adininistered. There is always a small concentration of cyanide (0.02 to 0.04 mg/L) in the blood, and the body has a mechanism for continuous removal of small amounts, such as from smoking, by converting it to thiocyanate, which is discharged in the urine. 

Recommended Exposure Limit (REL) was developed by the National Institute for Occupational Safety and Health (NIOSH) and defines the highest allowable airborne concentration that is not expected to injure a worker expressed as a ceiling limit of time-weighted average for an eight- to ten-hour work day. 

The TLV is not a single entity. The ACGIH defines three categories of TLV, namely, the time-weighted average (TLV-TWA), the short-term exposure limit (TLV-STEL), and the ceiling. Because these are proprietary terms, the U.S. Occupational Safety and Health Administration (OSHA) has adopted different terminology for essentially the same concepts, as follows ... 

The ability to define a reference population can be a substantial limitation. There may be insufficient information regarding the exposure history of the reference population to a particular contaminant of interest. It is important to know the range of values of a given biomarker in a normal population (NRC 1991), where normal is regarded as without occupational exposure or without observed or hypothetical environmental exposure. However, Schulte and Talaska (1995) point out that pristine populations are rare, so nonexposed populations generally have some exposure of widely varied extent. 

OSHA PEL-TWA (Occupational Health and Safety Administration, Permissible Exposure Limits - Time Weighted Average) (NIOSH, 2005) is defined analogous to the ACGIH-TLV-TWA, but is for exposures of no more than 10 h/day, 40 h/week. 

The US Congress passed the Occupational Safety and Health Act in 1970. This act created the Occupational Safety and Health Administration (OSHA) in the federal Department of Labor to establish and enforce safety standards for the workplace. OSHA standards are called permissible exposure limits (PELs). Many PELs have been adopted from ACGIH TLVs. TLVs are generally defined as air concentrations of chemicals that most workers can be exposed to for an 8 h workday, 40 h week for a working lifetime without suffering adverse effects. TLVs are not guaranteed as safe exposure levels for the entire population. Employers may also institute voluntary exposure limits either because an OSHA standard has not been promulgated for a xenobiotic of concern or because they want to apply an exposure limit that is more protective than either the PEL or the TLV. 

Fortunately the Health and Safety Executive (HSE) publishes each year a booklet called EH40, which lists the chemicals and dusts that are subject to control. The HSE defines two levels of control the maximum exposure limit (MEL), which must never be exceeded and the occupational exposure standard (OES) which is a realistic target for the workplace. 

Occupational exposure to phosgene" has been defined by NIOSH [1484] as exposure above half of the recommended time-weighted average (TWA) environmental limit whilst "overexposure" is defined as known or suspected exposure above either the TWA or ceiling concentration, or any exposure which results in the development of pulmonary symptoms. 

The Health and Safety at Work Act 1568/85, was the first attempt at modem health and safety legislation was which contained the general health and safety duties of employers, provisions for worker representation and requirements for employers in larger enterprises to appoint occupational healdi and safety professionals to advise them on carrying out their responsibilities. Article 26 of Chapter V (echoing Dir.80/1107/EEC) obliges the emplo r to take measures to avoid or minimize the exposure of workers to hazardous agents, wherever this is practicable. In all events the level of exposure must be lower that the level defined as the exposure limit value . 

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