Threshold Limit Value (TLV)

TLV is the average concentration of a substance to which workers may be exposed for a set time period. The values are expressed as part per million by volume of gas in air. 

TLV-TWA (Threshold Limit Value-Time Weighted Average) 

This is the average concentration of a substance to which workers may exposed for a normal 8 Hrs workday or a 40 Hrs week, day after day, without adverse effects.  Any reference to TLV on safety data sheets is usually the TLV-TWA. 

TLV-STEL ( Short Term Exposure Limit) 

This is the maximum concentration of a substance to which workers may be exposed for a maximum period of 15 minutes. Four such exposure are allowed during a working day with an interval of at least one hour between each. 

TLV-C (Ceiling) 

This is the upper limit above which workers should never be exposed to the substance. 

The main ways that exposure can occur are as follows:

1. Ingestion

2. Skin contact

3. Inhalation