Time Weighted Average (TWA)

Toxic gas limits related to concentration & time

Short Term Exposure Limit (STEL)

The maximum allowable concentration over 10 minutes.

Long Term Exposure Limit (LTEL)

The maximum allowable concentration over an 8 hour period.

Units of measure

Parts per million (ppm)

Milligrams per cubic metre (mg/m3)

Levels

COSHH

OSHA, NIOSH