Industrial hygiene sampling for airborne TDI in six flexible slabstock foam manufacturing facilities in the United States: a comparison of the short-term and long-term sampling data.

A majority of all the flexible polyurethane foams are produced by the continuous slabstock process using toluene diisocyanate (TDI) and polyether polyol. The commercially available TDI product is predominantly an 80:20 mixture of the 2,4-TDI and 2,6-TDI isomers. TDI can be used in many applications, but the market is dominated by the flexible slabstock foam industry. Even though there has been a considerable amount of industrial hygiene sampling conducted for airborne TDI in this industry, the focus of the sampling has generally included long-term (time-weighted average) monitoring with a limited amount of sampling for short-term (peak) episodes. By conducting only long-term sampling, which averages the exposure over some extended time period, these short-term episodes (i.e., tasks or activities) of peak exposure were often not characterized. To investigate whether long-term sampling was adequately predictive of short-term excursions, simultaneous (side-by-side) short-term and long-term breathing zone samples were collected on 31 flexible slabstock foam line employees at six manufacturing facilities throughout the United States. Four hundred three short-term samples averaging 15 minutes in length, and 78 long-term samples averaging 124 minutes in length were collected for four operator categories. From these 78 long-term samples, 31 eight-hour TWAs were projected (assuming no further exposure to airborne TDI for the remainder of the work shift) for comparison to the short-term samples. Based on the data collected, compliance with the current ACGIH TLV TWA of 5 ppb would also ensure compliance with the OSHA PEL-C of 20 ppb in a majority of the cases associated with the flexible slabstock foam industry provided that (1) the TLV TWA accounted for the 2,6-TDI isomer in addition to the 2,4-TDI isomer (at this time, exposure limits are published for only the 2,4-TDI isomer), and (2) the TLV TWA was compared to the partial shift TWA measured over the operational time of the workday rather than as an average over an eight-hour workday. Further, exceedences of the 20 ppb PEL-C did occur (e.g., when the foam line tunnel was entered, where there was an "upset" condition, or where there was close contact with hot [fresh cut] buns), but can be protected against with (1) improved work practices, (2) engineering controls, and (3) respiratory protection.