Exposure airborne concentrations

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. 

In humans, cases of dermatitis have been described after contact with DHBs. Combined exposure to hydroquinone and quinone airborne concentrations causes eye irritation, sensitivity to light, injury of the corneal epithelium, and visual disturbances (126). Cases with an appreciable loss of vision have occurred (127). Long-term exposure causes staining due to irritation or allergy of the conjunctiva and cornea and also opacities. Resorcinol and catechol are also irritants for eyes. 

Polyurethanes. These polymers can be considered safe for human use. However, exposure to dust, generated in finishing operations, should be avoided. Ventilation, dust masks, and eye protection are recommended in foam fabrication operations. Polyurethane or polyisocyanurate dust may present an explosion risk under certain conditions. Airborne concentrations of 25—30 g/m are required before an explosion occurs. Inhalation of thermal decomposition products of polyurethanes should be avoided because carbon monoxide and hydrogen cyanide are among the many products present. 

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. 

Short Term Exposure Limit (STEL) The time w eightcd average (TWA) airborne concentration to which workers may be e.xposed for periods up to 15 minutes, with no more than 4 such c.xcursions per day and at least 60 minutes between them. 

A 1,5-hour inhalation exposure of mixed breed rabbits to airborne concentrations of 72 ppm of hydrogen sulfide resulted in ventricular repolarization, while a 5-day, 0.5-hour/day exposure to this concentration resulted in cardiac arrhythmia (Kosmider et al. 1967). Histochemical staining of the myocardial cells revealed a reduction in adenosine tri-phosphate (ATP) phosphohydrolase and NADPH2 oxidoreductase (Kosmider et al. 1967). Cardiac arrhythmia, suggestive of a stimulus transmission disorder, was... 

Occupational Exposure Limits (OELs) refer to airborne concentrations of substances and provide a guide to their toxicity. 

AEGL-1 is the airborne concentration (expressed as ppm (parts per million) or mg/m3 (milligrams per cubic meter)) of a substance above which it is predicted that the general population, including susceptible individuals, could experience notable discomfort, irritation, or certain asymptomatic nonsensory effects. However, the effects are not disabling and are transient and reversible upon cessation of exposure. 

All these entry routes are controlled by the application of proper industrial hygiene techniques, summarized in Table 2-1. These control techniques are discussed in more detail in chapter 3 on industrial hygiene. Of the four routes of entry, the inhalation and dermal routes are the most significant to industrial facilities. Inhalation is the easiest to quantify by the direct measurement of airborne concentrations the usual exposure is by vapor, but small solid and liquid particles can also contribute. 

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. 

Threshold Limit Value Airborne concentrations of substances devised by the ACGIH that represent conditions under which it is believed that nearly all workers maybe exposed day after day with no adverse effect. TLV s are advisory exposure guidelines, not legal standards, based on evidence from industrial experience, animal studies, or human studies when they exist. There are three different types of TLV s Time Weighted Average (TLV-TWA) Short Term Exposure Limit (TLV-STEL) and Ceiling (TLV-C). (See also PEL)... 

Although a great many deaths have occurred from accidental, intentional, or occupational exposures to HCN, in only a few cases are specific exposure concentrations known. In a review of human fatalities (ATSDR 1997), it was stated that exposure to airborne concentrations of HCN at 180 to 270 ppm were fatal, usually within several minutes, and a concentration of 135 ppm was fatal after 30 min. The average fatal concentration for humans was estimated at 546 ppm for 10 min. The latter data point is based on the work of McNamara (1976), who considered the resistance of man to HCN to be similar to that of the goat and monkey and four times that of the mouse. Fatal levels of HCN cause a brief period of central nervous system stimulation followed by depression, convulsions, coma with abolished deep reflexes and dilated pupils, and death. Several review sources, such as Dudley et al. (1942),... 

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