Workplace exposure limit

Workplace exposure limits (WELs) were adopted in the UK in 2005 to replace maximum exposure limits (MELs) and occupational exposnre standards (OESs). Workplace exposure limits—longterm exposnre limits (eight-hour time-weighted average exposures) and short-term exposme limits (hfteen-minnte time-weighted average exposmes)—are set by the Health and Safety Executive (HSE) and pnblished in document EH40 (http //www.hse.gov.uk/coshh/tablel.pdf). 

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

Recommended Exposure Limits, REL, are set by the National Institute for Occupational Safety and Health, NIOSH, which is a part of the department of Health and Human Services. NIOSH scientists recommend exposure limits to OSHA, based on animal and human studies. NIOSH RELs are often more conservative than the TLV, and NIOSH s consideration of available research and studies is regarded as thorough.  

Time-Weighted Average, TWA, is the concentration of contaminants over an 8-hour period. It is determined by samphng the breathing zone of the woiker for 8 hours. It is expressed as follows when a series of successive samples have been taken  

To determine the level of exposure, the TWA reading is compared with a standard such as the threshold limit value, TLV, or permissible exposure limit, PEL. If the reading exceeded the standard, overexposure occurred.  

Short-Term Exposure Limit, STEL, is a 15-minute TWA concentration that may not be exceeded, even if the 8-hour TWA is within the standards. TWA-STEL are given for contaminants for which short-term hazards are known. For the rest, an excursion factor of 3 has been often used STEL should not exceed 3 times the TWA limit.  

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Sources of human exposure to formaldehyde are engine exhaust, tobacco smoke, natural gas, fossil fuels, waste incineration, and oil refineries (129). It is found as a natural component in fmits, vegetables, meats, and fish and is a normal body metaboHte (130,131). FaciUties that manufacture or consume formaldehyde must control workers exposure in accordance with the following workplace exposure limits in ppm action level, 0.5 TWA, 0.75 STEL, 2 (132). In other environments such as residences, offices, and schools, levels may reach 0.1 ppm HCHO due to use of particle board and urea—formaldehyde foam insulation in constmction. 

Health and Safety Factors. Malononitrile is usually available as a soHdifted melt in plastic-Hned dmms. Remelting has to be done carefully because spontaneous decomposition can occur at elevated temperatures, particularly above 100°C, in the presence of impurities such as alkaHes, ammonium, and 2inc salts. Melting should be carried out by means of a water bath and only shordy before use. Occupational exposure to malononitrile mainly occurs by inhalation of vapors and absorption through the skin. Malononitrile has a recommended workplace exposure limit of 8 mg/m, an LD q (oral, rats) of 13.9 mg/kg, and is classified as slight irritant (skin irritation, rabbits). Transport classification RID/ADR 61, IMDG-Code 6.1, lATA/ICAO 6.1. 

Toxicity Data on Af- Vinyl-2-Pyrrolidinone. Results of a chronic inhalation study in rats warrant a review of industrial hygiene practices to assure that VP vapor concentrations are maintained at a safe level. One of the manufacturers, ISP, recommends that an appropriate workplace exposure limit be set at 0.1 ppm (vapor) (9). Additionally, normal hygienic practices and precautions are recommended, such as prompt removal from skin and avoidance of ingestion. In case of accidental eye contact, immediately flush with water for at least 15 minutes and seek medical attention. Refer to the manufacturers Material Safety Data Sheets for more detailed information. Table 3 provides some toxicity data. 

Beryllium, beryllium-containing aUoys, and beryUium oxide ceramic in soHd or massive form present no hazard whatsoever (31). SoHd shapes may be safely handled with bare hands (32) however, care must be taken in the fabrication and processing of beryUium products to avoid inhalation of airborne beryUium particulate matter such as dusts, mists, or fumes in excess of the prescribed workplace exposure limits. Inhalation of fine airborne beryUium may cause chronic beryUium disease, a serious lung disease in certain sensitive individuals. However, the vast majority of people, perhaps as many as 99%, do not react to beryUium exposure at any level (33). The biomedical and environmental aspects of beryUium have been summarized (34). 

Safe Exposure Levels. The U.S. Occupational Safety and Health Administration (OSHA) has adopted workplace exposure limits designed to keep airborne concentrations weU below the levels known to cause health problems (35) including ( ) daUy time-weighted average (TWA) exposure over an eight-hour day is not to exceed beryUium concentrations of 2 lg/m of air and (2) short-term exposure should not exceed beryUium concentrations of 25... 

Workplace exposure limits for benzene have been regulated to levels as low as 0.5 ppm (43). Industrial emissions affecting the pubHc ate now low enough that the EPA considers that a greater hazard exists from mosdy indoor sources such as smoking, automobile exhausts, and consumer products (44). 

One of the manufacturers, ISP, recommends that an appropriate workplace exposure limit be set at 0.1 ppm (vapor). In case of accidental eye contact, immediately flush with water for at least 15 minutes and seek medical attention. 

There is no medical or laboratory test that can accurately measure the amount of epoxy components in the human body, and most of the chemicals found in epoxy systems are not stored in the body. Regional environmental regulators set and enforce workplace exposure limits. These exposure limits are generally set for some of but not all the epoxy components that one may contact. 

In the United Kingdom the Occupational Exposure Standards and Maximum Exposure Limits were replaced in 2005 by Workplace Exposure Limits and principles of good practice . The Occupational Exposure Standards and Maximum Exposure Limits were transferred to the new Workplace Exposure Limit system but those exposure limits for which there was insufficient evidence that they protect human health, were withdrawn (Walters and Grodzki 2006). 

UK - Health and Safety Executive (2005) List of approved workplace exposure limits, http // www.hse.gov.uk/coshh/tablel.pdf. Cited March 2007. 

Solvents that are currently assigned a workplace exposure limit (eight-hour long-term exposure limit) that is less than or equal to 100 ppm are marked in Table 11.7 with an arrowhead ( ) (data from EH40/2005). 

Trichloroethane levels in the workplace are regulated by the Occupational Safety and Health Administration (OSHA). The workplace exposure limit for an 8-hour workday, 40-hour workweek is 350 ppm in air. See Chapter 7 for more information on regulations and advisories regarding... 

The UK introduced a new framework for OELs in 2005. The two limit level system (occupational exposure standards - OES and maximum exposure limits - MEL) of the previous decade was replaced with a single limit (Workplace Exposure Limit -WEL) system in a revised legislative framework for chemical hazards. Under the old system, if the HSE believed a substance merited an DEL, and there was no relevant EU limit, it supplied information on a substance to the Working Group for the Assessment of Toxic Chemicals (WATCH), a sub-committee of the HSC s tripartite Advismy Committee on Toxic Substoces (ACTS) ... 

Based on these conclusions a Consultation Document was published that made proposals to introduce a new OEL Framework (HSC 2003) that was a combination of the second and third options described in the Discussion Document. It reiterated the belief that many employers, particularly in small firms, did not know about OELs and of those that did, very few understood how to work out whether the chemicals in the air at their workplaces were above or below the relevant OELs. Because of this and other work on small firms it argued that a new approach was necessary. It advocated the replacement of the two types of OELs that had been in use since the mid-1980s (the OES and MEL) with a single type of OEL to be known as a workplace exposure limit (WEL). Employers would be required to ensure that the amount of chemical in workplace air did not exceed the WEL. However, since it was recognised that only for very few chemicals was there sufficient information to be able to say with certainty that harm would not occur to anyone exposed at the WEL, it was not possible to regard them as safe limits . Since it was essential that such uncertainties be accounted for in any system that aimed to protect workers properly a new COSHH Regulation 7 (7) replaced the COSH 2002 Reg. (7) and 7 (8). It stated ... 

United Kingdom Health and Safety at Work etc. Act 1974 Control of Substances Hazardous to Health Rfi lations 2004, SI 2004 No.2677 Chemicals (Hazard Information and Packaging for Supply) Regulations 1994, SI 2002, No, 1689 H40 005 Workplace exposure limits Containing the list of woikplace exposue limits for xise widi die Control of Substances Hazardous to health Regulations 2002 (as amended), Environm tal Hygiene Guidance Note EH 40, HSE Books 2005. 

NIOSH recommendations are published in a variety of documents. Criteria documents recommend workplace exposure limits and appropriate preventive measures to reduce or eliminate adverse health effects and accidental injuries. 

II. Toxic dose. The fatal oral dose of methanol is estimated to be 30-240 mL (20-150 g). The minimum toxic dose is approximately 100 mg/kg. Elevated serum methanol levels have been reported after extensive dermal exposure and concentrated Inhalation. The ACGIH recommended workplace exposure limit (TLV-TWA) for inhalation is 200 ppm as an 8-hour time-weighted average, and the level considered immediately dangerous to life or health (IDLH) is 6000 ppm. 

A. Phosphine gas. The ACGIH-recommended workplace exposure limit (TLV-TWA) Is 0.3 ppm (0.42 mg/m, much lower than the minimal detectable (fishy odor) concentration of 1-3 ppm. Hence, the odor threshold does not provide sufficient warning of dangerous concentrations. An air level of 50 ppm is considered immediately dangerous to life or health (IDLH). Chronic exposure to sublethal concentrations for extended periods may produce toxic symptoms. 

NIOSH Pocket Guide to Occupational Hazards http //www.cdc.gov/nlosh/npg/npgdOOOO.html. (An excellent summary of workplace exposure limits and other useful Information about the most common Industrial chemicals.)... 

A substance for which there is community workplace exposure limits. 

Cyanogen bromide is a volatile solid, which dissolves readily in water, diethyl ether, and alcohol. It is a highly toxic substance through inhalation, ingestion and skin contact. It is usitally considered about 2-3 times less toxic than hydrogen cyanide, but the exact lethal dose is imknown. In the developed coirrttries, the permissible workplace exposure limits in the air are 5 mg/m (as cyanide, time-averaged concentration in an 8-h shift), and 20 mg/m (as cyanide, peak concentration). 

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