10 February 2001

The American Conference of Governmental Industrial Hygienists (ACGIH) has proposed a new threshold limit value (TLV) for diesel exhaust particulates. The new TLV, published in the Notice of Intended Changes for 2001 (ACGIH Today, 2001, 9(1)), is listed at 0.02 mg/m3 with carcinogenicity notation A2 - “Suspected Human Carcinogen”. Diesel particulates are measured as elemental carbon.

Diesel particulates have remained on the ACGIH list of intended changes since 1995/96, but the TLV has never been finalized. The first proposal (1995/96) called for a TLV of 0.15 mg/m3. In its 1999 Notice of Intended Changes, the ACGIH tightened the proposed TLV to 0.05 mg/m3.

No particulate matter definition or measuring method has been specified in the previous proposals. Assuming that the 0.05 mg/m3 limit represented total particulate matter (including elemental carbon, organic carbon, sulfates, and metal ashes), the current proposal does not tighten the 1999 TLV; it merely clarifies the measuring method. Typically, the elemental carbon fraction constitutes about 40% of total diesel particulate matter.

The ACGIH publishes annually a table of TLV values for a number of chemical substances and physical agents. The TLVs set by ACGIH are developed as recommendations or guidelines to be used in the practice of industrial hygiene, which establish the maximum ambient concentrations of toxic chemical substances. Formally, they are not legal standards. However, regulatory authorities follow the ACGIH recommendations in their law-making activities.