Gases threshold limit averages

Butadiene is a colorless, odorless, flammable gas, with a bp of -4.7°C. As of 2000 butadiene has been on the Known to Be a Human Carcinogen list of the Department of Health and Human Services. It has a time-weighted average threshold limit value (TLV) of 2 ppm. TLVs and carcinogens will be discussed more fully under benzene. Butadiene is expensive to store because it polymerizes easily and must be refrigerated. 

As an index for toxicity of gaseous substances, the median lethal concentration (LC 5 0 ) and the threshold limit value (TLV) are used to evaluate acute toxicity. LCso is the gas concentration (ppm) in air which results in the death of 50% of a population of test animals by inhalation. TLV is the threshold limit of exposure which does not cause any serious sickness in workers under normal conditions of an 8 hours day and a 40-48 hour work week. TLV is usually given in combination with the time-weighted-average concentrations for 8 hours per day (TLV—TWA), or with the short time exposure limit (TLV-STEL), which is that exposure which should not be exceeded even for a relatively short period (15-30 minutes), or with the ultimate limit (TLV-C), which defines the exposure level that should not be exceeded under any circumstances. 

Adopted Threshold Limit Falues - Time Weighted Average (TLV-TWA) - in parts of vapour or gas per million parts of contaminated air by volume (mL/m ppm) at 25 °C and 1013 hPa, and in approximate milligrams of substance per cubic metre of air (mg/m ). 

Specific concentration limit refers to a critical gas concentration limit that should not be exceeded. This limit can be a Threshold Limit Value (TLV), Time Weighted Average (TWA), Permissible Exposure Limit (PEL), Short Term Exposure Limit (STEL), Lower Explosive Limit (LEL) or Immediate Danger to Life and Health (IDLH) limit. These limits can be defined in terms of percent volume (%), parts per million (PPM), or even parts per billion (PPB) Table 1 lists hazards and exposure limits for several common hazardous gases foimd in the electronics industry. Critical gas concentration limits may be mandated by environmental, health and safety statutes, regional or local codes, local code enforcement officials, internal risk management personnel, or an established organizational policy. 

American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Values (TLVs). The values shown are the currently adopted Time Weighted Averages (TWAs) in parts of vapor or gas per million parts of contaminated air by volume at 25 C and 760 ton. Compiled from (11) and used by permission of ACGIH. See Section 12.4 and (11) for a discussion of TLVs and their use. 

In the photoelectric method, the measured average work function is always less than the true since patches of high work function tend to be excluded from the emission process. Thus, the nonuniform distribution of adsorbate on a patch surface may cause a slight discrepancy in the evaluation of A. Experimentally, the photoelectric method has various limitations. Photocurrents of the order of 10 A. must be measured accurately in the region of vo, and for films of work function greater than 5 v., the threshold frequency lies in the far ultraviolet—a practical disadvantage. Furthermore, the method is inapplicable at pressures in excess of 10 mm. Hg because of ionization of the gas by collision. 

It is important to have reliable laser diagnostics, preferably on a shot-to-shot basis this is possible for a 10 Hz system. To characterise the temporal profile of the pulses, single-shot spectra and autocorrelation data can establish whether the laser pulses are Fourier-transform limited. For lasers with a sech profile, a product AvAtxO.32 should be achieved. It is also important to monitor the focal spot, its Airy disc and average intensity. Alternatively, a reasonable measure of the focused intensity can be obtained using Xe gas and the known threshold intensities for producing the various stages of ionization [12]. 

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