Definitions of Terms in Chemical Safety
Threshold
Limit Value (TLV) Air-borne
concentration of toxic substances which nearly all personnel involved may by
repeatedly exposed day after day without adverse effect. TLV values are
expressed in ppm (parts per million) or mg/m3.
Time
Weighted Average (TLV-TWA) is the time weighted average concentration for a normal eight hour day or
40 hr week. Nearly all persons can be exposed day after day to airborne
concentrations at these limits without any adverse effect.
Asphyxiant is a gas, exposure to which leads to a morbid condition caused by the failure of the tissues to receive or utilize oxygen, the fault occurring in the lungs, blood or tissues or caused by dilution of atmospheric oxygen.
Confined Space Physical Hazards – Part 2
Simple
asphyxiants are physiologically
inert substances that dilute oxygen in the air. Examples are nitrogen,
hydrogen, helium, methane and carbon dioxide.
Chemical
asphyxiants are
substances that interfere with the supply or utilisation of oxygen in the body
by chemically reacting with blood, e.g., carbon monoxide and hydrogen cyanide.
Flammable
Limit - A flame can
propagate in a mixture of flammable gas and air (or oxygen) only if the
concentration of the gas is between two limits known as the lower and upper
flammable limits.
Lower Flammable Limit (LFL) - The minimum percent by volume of flammable vapor in air below which flame will not propagate in the mixture.
Process Safety Incidents - Case Studies
Upper
Flammable Limit (LFL) – The maximum percent by volume of flammable vapor in air above which
flame will not propagate .in the mixture.
CAS Number - Chemical Abstract Service. Registry of chemicals by assigning
numerical identification
Chronic Health Effect - An adverse effect with symptoms that develop or recur very slowly,
or over long periods of time as a result of continued or periodic exposure to
the offending agent
Acute Health Effect - A severe effect which occurs rapidly after a brief intense exposure to a substance. ANSI - American National Standards Institute is a private group that develops consensus standards.
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