Limiting Short-Term Exposure

2 Limiting Short-Term Exposure 2.6.2.1 Threshold Values 

The SEL (Seuil d Eflfet Letal) [54] and DTL (Dangerous Toxic Load) [55] values are mainly targeted at land-use planning. Only the ACUTEX method of the European Community [56] provides values for land-use and emergency planning. 

Whilst threshold values merely enable one to take good or bad decisions a probit ( probability unit (-relation allows one to assess the probability of a certain consequence, e.g. death, occurring due to a causative factor such as toxic exposure. For example, we have for the exposure to chlorine 

54) C(t ) denotes the variation with time of the chlorine concentration. Generally the time integral over a concentration is called dose. However, if an exponent 1 is applied to the concentration we speak of load, e.g. in this case toxic load. 

Probit relations are formulated such that they adopt the value Y = 5 for a damage probability of 0.5. This corresponds to the lethal dose 50, LD50, a value at which 50 % of the affected individuals are expected to die. 

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TSIIOSH REL-STEL (Recommended Exposure Limits - Short Term Exposure Limit) (NIOSH, 2005) is defined analogous to the ACGIH TLV-TWA. 

PEL-STEL (OSHA) permissible exposure limit-short-term exposure limit... 

Table 2-8 shows the mass equivalents for natural and depleted uranium for radiation levels that caused potential radiological effects in rats exposed once for 100 minutes to airborne 92.8% enriched uranium with an estimated specific activity of 51.6 pCi/g (Morris et al. 1989). These mass equivalent values for natural and depleted uranium for the minimal concentration of radioactivity that is expected to induce potential radiological effects are well above levels that would be expected to be inhaled or ingested. In addition, the mass equivalents for natural and depleted uranium for potential radiological effects are 3,600 and 76,500 times higher, respectively, than the occupational exposure limits (short-term exposure) recommended by the National Institute for Occupational Safety and Health (NIOSH 1997). Therefore, MRLs for uranium based on studies that used enriched uranium are inappropriate. 

Maximum use concentration (MUC) means the maximum atmospheric concentration of a hazardous substance from which an employee can be expected to be protected when wearing a respirator, and is determined by the assigned protection factor of the respirator or class of respirators and the exposure limit of the hazardous substance. The MUC can be determined mathematically by multiplying the assigned protection factor specified for a respirator by the required QSHA permissible exposure limit, short-term exposure limit, or ceiling limit. When no QSHA exposure limit is available for a hazardous substance, an employer must determine an MUC on the basis of relevant available information and informed professional judgement. 

IDLH (Immediately Dangerous to Life and Health, National Institute cf Occupational Safety and Health) (NIOSH, 2010) represents the maximum concentration from which one could escape within SOmin without any escape-impairing symptoms, or any irreversible hmlth fffects. The IDLHfor phosgene is based on acute inhalation toxicity data in humans (Diller, 1978). NIOSH REL-STEL (Recommended Exposure Limits—Short Term Exposure Limit) (NIOSH, 2010) is dffined analogous to the ACGIH TLV-TWA. 

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. 

Use of isopropyl alcohol in industrial appHcations does not present a health hazard. The alcohol produces anesthetic effects in high vapor concentration. Consequently, the OSHA permissible exposure limit (PEL) and the ACGIH threshold limit value (TLV) have been estabUshed at 400 ppm (0.098 mg/L) for an 8-h exposure (TWA) (138). This level causes a mild irritation of the eyes, nose, and throat (139). However, the TLV level does not produce symptoms of anesthesia (140). The OSHA and ACGIH short-term exposure limits (STELs) are 500 ppm. The odor threshold for isopropyl alcohol ranges from 3 to 200 ppm, which is the minimum concentration having identifiable odor (141). 

Health, Safety, and Environmental Factors. Sulfur dioxide has only a moderate acute toxicity (183). The lowest pubHshed human lethal concentration is 1000 ppm for 10 months. The lowest pubHshed human toxic concentration by inhalation is 3 ppm for 5 days or 12 ppm for 1 hour. The lowest pubHshed human lethal concentration is 3000 ppm for 5 months. In solution (as sulfurous acid), the lowest pubHshed toxic dose is 500 flg/kg causing gastrointestinal disturbances. Considerable data is available by other modes of exposure and to other species NIOSH standards are a time-weighted average of 2 ppm and a short-term exposure limit of 5 ppm (183). 

The adopted values for TWAs for airborne vanadium, including oxide and metal dusts of vanadium, is 0.5 mg/m the values for fumes of vanadium compounds is 0.05 mg/m. These limits are for normal 8-h workday and 40-h work-week exposures. The short-term exposure limit (STEL) is 1.5 mg/m for dusts (25). A description of health ha2ards, including symptoms, first aid, and organ involvement, personal protection, and respirator use has beenpubhshed (26). 

Effective Dec. 10, 1987, the existing standard for benzene was amended under OSHA (29 CER, Part 1910.1028). The revised standard reduced the permissible exposure limit from 10 ppm (32 mg/m ) to 1 ppm (3.2 mg/m ) iu an 8-h TWA. The short term exposure limit (STEL) of 5 ppm was set over a 15 min period. The standard also established action level requirements for exposure over 0.5 ppm. 

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... 

Because pulp bleaching agents are, for the most part, reactive oxidising agents, appropriate precautions must be taken in their handling and use. For example, it is important to ensure that the threshold limit values (TLV) (20) in Table 2 are not exceeded in the workplace air. These are airborne concentrations in either parts per million by volume under standard ambient conditions or mg per cubic meter of air. They "represent conditions under which it is beUeved that nearly all workers may be repeatedly exposed, day after day, without adverse effect" (20). TWA refers to a time-weighted average for an 8-h workday STEL is a short-term exposure limit or maximum allowable concentration to which workers can be continuously exposed for 15 minutes. 

The threshold limit value—time integrated average, TLV—TWA, of chlorine dioxide is 0.1 ppm, and the threshold limit value—short-term exposure limit, STEL, is 0.3 ppm or 0.9 mg /m of air concentration (87,88). Chlorine dioxide is a severe respiratory and eye irritant. Symptoms of exposure by inhalation include eye and throat irritation, headache, nausea, nasal discharge, coughing, wheezing, bronchitis, and delayed onset of pulmonary edema. Delayed deaths occurred in animals after exposure to 150—200 ppm for less than one hour. Rats repeatedly exposed to 10 ppm died after 10 to 13 days of exposure. Exposure of a worker to 19 ppm for an unspecified time was fatal. The ingested systemic effects of low concentration chlorine dioxide solutions are similar to that of chlorite. 

The toxic plume is expected to extend 4000 meters downwind at concentrations above the short-term exposure limit (STEL). 

Another way to evaluate risks is to calculate the sensitivity of the total risk estimates to changes in assumptions, frequencies, or consequences. Risk analysts tend to be conservative in their assumptions and calculations, and the cumulative effect of this conservatism may be a substantial overestimation of risk. For example, always assuming that short-term exposure to chemical concentrations above some threshold limit value will cause serious injury may severely skew the calculated risks of health effects. If you do not understand the sensitivity of the risk results to this conservative assumption, you may misallocate your loss prevention resources or misinform your company or the public about the actual risk. 

TLV-STEL, THRESHOLD LIMIT VALUE - SHORT TERM EXPOSURE LIMIT (USa) A maxilHUm limit On the... 

Short-term exposure limit (STEL) TLV - the eoneentration to whieh it is believed that workers ean be exposed eontinuously for a short period of time without suffering from initation, ehronie or irreversible tissue damage, or nareosis of suffieient degree to inerease the likelihood of aeeidental injury, impair self-reseue or materially reduee work effieieney, and provided that the daily TWA limit is not exeeeded. A STEL is a 15 min TWA exposure whieh should not be exeeeded at any time during the work day even if the TWA is within the TLV. It should not oeeur more than four times per day or without at least one hour between sueeessive exposures. 

Short-term exposure limits. These are eoneerned primarily with the avoidanee of aeute effeets, or redueing the risk of the oeeurrenee. 

Speeifie short-term exposure limits are listed by the HSE for those ehemieals whieh pose a risk of aeute effeets sueh as eye irritation from brief exposures. Eor other ehemieals a reeommended... 

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