Exposure limit of toxic substance

• The toxic hazards to which personnel are exposed in tanker operations arise almost entirely from exposure to gases of various kinds such as H2S, Benzene, Mercaptan, etc.,

• A number of indicators are used to measure the concentrations of toxic vapours and many substances have been assigned Threshold Limit Values (TLVs), sometimes referred to as Permissible Exposure Limits (PELs).

• Exposure limits may be set by international organisations, national administrations or by local regulatory standards. Any limits established by regulation should not be exceeded.

• Where a PEL is not available for an airborne contaminant, other Occupational Exposure limits such as the Threshold Limit Values (TLVs) published by the American Conference of Governmental Industrial Hygienists (ACGIH) may be used. The values quoted are expressed as Threshold Limit Values (TLVs) in parts per million (ppm) by volume of gas in the air.

Threshold limit value (TLV)

• Is referred to airborne concentrations of substances under which it is believed that nearly all workers may be exposed day after day with no adverse effect.

There are three different types of TLV's:

Time Weighted Average (TLV-TWA) 

• The airborne concentrations of a toxic substance averaged over an 8 hour period, usually expressed in parts per million (ppm).

Short Term Exposure Limit (TLV-STEL)

• The airborne concentration of a toxic substance averaged over any 15 minute period, usually expressed in parts per million (ppm).

Ceiling (TLV-C) 

• The concentration that should not be exceeded during any part of the working exposure.

Extracted from MSDS