Some Definitions
Threshold Limit Value (TLV): It expressed as parts of vapour or gas per million parts of air (PPM) by volume at 25 'c and 760 mm Hg.
Threshold Limit Value-Time Weighted Average (TLV-TWA): The time weighted average concentration for a normal 8 hours work/day and 40 hours work/week to
Which nearly all workers may be repeatedly exposed, day after day without adverse effect.
Threshold Limit Value Short Term Exposure Limit (TLV - STEL): The concen- tration to which workers can be exposed continuously for a short period of time without suffering from Irritation, chronic or irreversible tissue change or narcosis of sufficient degree to increase the likelihood of accidental injury, impair self-rescue or materially reduce work efficiency, and provided that the daily TWA-STEL also is not exceeded. It is not a separate independent exposures limit, rature it supplements the time weighted average (TWA) limit, where there are recognized acute. effects from a substance whose toxic effects are primarily of a chronic nature. STEL is recommended only where toxic effects have been reported from high short term exposures in either humans or animals.
A STEL is defined as 15-minute time weighted average exposure which should not be exceeded at any time during a work day even if the 8-hour time weighted average is within the TLV. Exposures at STEL should not be longer than 15 minutes and should not be repeated for more than 4 times a day. There should be at least 60 minutes between successive exposures at the STEL. An averaging period other than 15 minutes may be recommended when this is warranted by observed biological effects.
Maximum Allowable. Concentration (MAC): It is the maximum concentration of a toxic substance which should not be exceeded or violated even for a short period of time.
Maximum Allowable. Concentration (MAC): Threshold Limit Value-Ceiling (TLV-C): It is the concentration that should not be exceeded even instantaneously.
Threshold Limit Value-Ceiling (TLV-C): Immediately Dangerous to Life and Health (IDLH): It is a condition that poses immediate danger to life and health. IDLH limits were created to assist in making decisions regarding respirator use.
Supplied air respirators should only be used above IDLH limit. Air purifying respirators may be used below IDLH limit, if appropriate. Workers should not be in an IDLH environment for a long period of time unless they are equipped and protected to be in that environment.
Cf.section 41F (Permissible limits of exposure of chemical and toxic substances) Schedule I&II and 91 A (Safety and occupational health surveys) of Factory Act 1948 and Kerala Factory Rules 81AJ (Occupational health centers), 81AK (Ambulance van) & 81AL (Decontamination facilities), 129A Table I (Permissible levels of certain chemical substance in work environment).