EXPOSURE LIMIT

Permissible Exposure Limit (PEL) is a legally binding airborne exposure limit issued by the Occupational Safety and Health Administration (OSHA) 

Threshold Limit Value (TLV) is issued by the American Conference of Governmental Industrial Hygienists (ACGIH). TLVs are recommended exposure limits and should be used as guidelines for good practice. 

A Time Weighted Average (TWA) is for a normal 8 h workday and 40 h work week to which workers can be subjected day after day without adverse effect. 

The PEL and TLV-TWA for synthetic graphite is 10 mgm of total dust, 5mgm for synthetic graphite respirable dust and 2.5 mgm for natural graphite respirable dust. Zustra [20] has specified an air standard of 5 carbon fibers/cc, whilst the US Navy has a limit of 3 carbon fibers/cc. 

For longer term exposures throughout the day and workweek, the time-weighted average (TWA) is used, which for a standard 8-hour day is calculated as 

The limits for acceptable exposure to chemicals hazardous to health through inhalation for the UK are given in the HSE s publication EH40/(latest issue), Occupational exposure limits . This publication is re-issued each year and contains the latest limit values based on the various criteria used. 

Similar occupational exposure limits have been adopted by the EU -known as Indicative Occupational Exposure Values (lOEVs). These EU limit values take precedence over national limits. The levels quoted in the current edition of EH 40 incorporate the lOEVs. 

There are two types of occupational exposure limit which have different criteria  

X- can give short- and long-term integrated exposure 

X- with cellulose dust need to condition filter before and after test. EH40/(latest issue)  

X- give instantaneous reading X- continuous reading s- incorporate warning alarm 

The data given in EH40 is not absolute and should be taken as a guide to the standards to be achieved. It is incumbent upon all employers to endeavour to reduce exposures to below the limits quoted. 

In general, the guidelines established for radiation exposure have had as their principle objectives (1) the prevention of acute radiation effects (e.g., erythema, sterility), and (2) the limiting of the risks of late, stochastic effects 

Many of the recommendations of the ICRP and other radiation protection groups regarding radiation exposure have been incorporated into regulatory requirements by various countries. For the U.S. Department of Energy facilities, radiation exposure limits are found in Title 10, Part 835 of the Code of Federal Regulations (10CFR835). Table 3.1 provides a summary of the dose limits for occupational external exposures. 

General employee whole body (internal + external) 

General employee hands, arms below the elbows, feet, legs below the knee 

General employee any organ or tissue (other than lens of the eye) and skin Declared pregnant worker fetus/embryo (internal and external) 

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Exposure limits (threshold limit value or TLV) are those set by the Occupational Safety and Health Administration and represent conditions to which most workers can be exposed without adverse effects. The TLV value is expressed as a time weighted average airborne concentration over a normal 8-hour workday and 40-hour workweek. 

POLYETTiERS - TETRAHYDROFURAN AND OXETANE POLYTffiRS] (Vol 19) PEL. See Permissible exposure limit. 

Health and Safety Factors. See "General Health and Safety Eactors." The following toxicides for adiponitrile have been reported oral LD q (rats), 300 mg/kg dermal LD q (rabbits), 2,134 mg/kg and inhalation 4-h LC q (i ts), 1.7 mg. NIOSH has proposed an exposure limit of 4 ppm as a TWA (68). 

Material Safety Data Sheets (MSDS) issued by suppHers of acetone ate requited to be revised within 90 days to include new permissible exposure limits (PEL). Current OSHA PEL (54) and ACGIH threshold limit values (TLV) (55) ate the same, 750 ppm TWA and 1000 ppm STEL. Eot comparison, the ACGIH TWA values for the common mbbing alcohols are ethyl, 1000, and isopropyl, 400 ppm. A report on human experience (56) concluded that exposure to 1000 ppm for an 8-h day produced no effects other than slight, transient irritation of the eyes, nose, and throat. 

Air Contaminants—Permissible Exposure Limit," Title 29 Code of Federal Regulations Part CFR 1910.1000, OSHA, 1989, p. 3112. 

The 2-cyanoacryhc esters have sharp, pungent odors and are lacrimators, even at very low concentrations. These esters can be irritating to the nose and throat at concentrations as low as 3 ppm eye irritation is observed at levels of 5 ppm (13). The TLV for methyl 2-cyanoacrylate is 2 ppm and the short-term exposure limit is 4 ppm (14). Good ventilation when using the adhesives is essential. 

Exposure limits for siHcon carbide and powders of zirconium compounds (including zirconium dioxide) have been estabHshed by ACGIH. TLV—TWA s are 10 mg/m and 5 mg/m, respectively. OSHA guidelines for zirconium compounds call for a PEL of 5 mg/m. There are no exposure limits for siHcon nitride powder, but pmdent practice suggests a TLV—TWA of 0.1 mg/m. The soHd ceramics present no apparent health hazard. In machining such ceramics, however, care should be taken to prevent inhalation of respirable particles in amounts in excess of estabHshed limits. Disposal should be in approved landfills the materials are inert and should pose no danger to the environment. 

The toxicological problems associated with asbestos have been widely pubHshed and asbestos has been banned from most uses by the EPA. However, modem diaphragm cell chlorine plants have not had difficulty meeting the required exposure limits for asbestos fibers, and, as of 1990, the chlorine industry had an exemption allowing the continued use of asbestos as a diaphragm material. 

The inhalation toxicity of NF on animals has been studied extensively (37—40). These studies provide the basis of emergency exposure limits (EEL) that have been proposed for NE. The NAS—NRC Committee on Toxicology recommends that the EEL for NE be 10 min at 2250 ppm, 30 min at 750 ppm, and 60 min at 375 ppm. Gaseous NE is considered to be innocuous to the skin and a minor irritant to the eyes and mucous membranes. NE does give a weakly positive metabotically activated Ames test but only at concentrations greater than 2% or 10 times the 10 minute EEL. 

Stannous fluoride is used in dentifrices and dental preparations. The OSHA permissible exposure limit (44) and ACGIH (45) estabUshed TLV for fluoride is 2.5 mg/m of air. 

Handling and Toxicity. Tungsten hexafluoride is irritating and corrosive to the upper and lower airways, eyes, and skin. It is extremely corrosive to the skin, producing bums typical of hydrofluoric acid. The OSHA permissible exposure limits is set as a time-weighted average of 2.5 mg/kg or 0.2 ppm (22). 

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. 

Exposure to formic acid vapor causes irritation of the eyes and respiratory tract. The TLV/TWA occupational exposure limit is 5 ppm (40). Self-contained breathing apparatus should be used when there is a risk of exposure to high vapor concentrations. 

Sensitivity. The sampling and analytical method together should ideally have a limit of detection much less than the exposure limit. Less sensitive methods are stiU usable, however, as long as the limit is easily within the range of the method. 

Da.ta. Ana.lysls. First, the raw data must be converted to concentrations over an appropriate time span. When sample periods do not correspond to the averaging time of the exposure limit, some assumptions must be made about unsampled periods. It may be necessary to test the impact of various assumptions on the final decision. Next, some test statistics (confidence limit, etc) (Fig. 3) are calculated and compared to a test criteria to make an inference about a hypotheses. 

Colorado has a monthly mean. The OSHA permissible exposure limit (PEL) for lead is 50 at an action level (local authorities must investigate) of... 

However, if air sampling estabHshes that the lead exposure concentration is excessive, engineering controls (such as improved ventilation), adrninistrative controls (such as job rotation), and work practices (such as improved personal hygiene of workers) have to be appHed to comply with the permissible exposure limit (PEL) of the OSHA standard. 

Mg(OH)2 powder is classified by OSHA as a nuisance dust. ACGIH categorizes the powder form as particulates not otherwise classified. Exposure limits are as follows (108) ACGIH 10 mg/m , OSHA 5 mg/m (respirable), and 15 mg/m (total). Magnesium hydroxide is reported in the EPA TSCA inventory (109). 

Safety. Magnesium oxide (fume) has a permissible exposure limit (PEL) (134) (8 hours, TWA), of 10 mg/m total dust and 5 mg/m respirable fraction. Tumorigenic data (intravenous in hamsters) show a TD q of 480 mg/kg after 30 weeks of intermittent dosing (135), and toxicity effects data show a TC q of 400 mg/m for inhalation in humans (136). Magnesium oxide is compatible with most chemicals exceptions are strong acids, bromine pentafluoride, chlorine trifluoride, interhalogens, strong oxidizers, and phosphorous pentachloride. 

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. 

Value is a PEL C, ie, permissible exposure limit ceiling exposure limit. 

Fig. 5. Long-term magnetic field exposure limits for general public exposures in uncontrolled environment, where A is the 50/60 Hz window, according to B, IRPA C, VDE (Germany) D, NRPB (U.K.) and E (IEEE C95.1, 1991). To convert T to G, multiply by 10/...

It is good practice to keep concentrations of airborne nickel in any chemical form as low as possible and certainly below the relevant standard. Local exhaust ventilation is the preferred method, particularly for powders, but personal respirator protection may be employed where necessary. In the United States, the Occupational Safety and Health Administration (OSHA) personal exposure limit (PEL) for all forms of nickel except nickel carbonyl is 1 mg/m. The ACGIH TLVs are respectively 1 mg/m for Ni metal, insoluble compounds, and fume and dust from nickel sulfide roasting, and 0.1 mg/m for soluble nickel compounds. The ACGIH is considering whether to lower the TLVs for all forms of nickel to 0.05 mg/m, based on nonmalignant respiratory effects in experimental animals. 

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