Skin absorption of isocyanates: Use of MDI adhesive

The Challenge

During the manufacture of industrial flooring, chipboard panels were coated with isocyanate-based adhesive (MDI, methyl diphenyl diisocyanate) before metal facing plates were manually attached to either side. The panel was then mechanically crimped prior to being manually taken off the production line for storage. The workers were wearing leather gloves, primarily for protection against physical injury during the manual tasks. Urine samples showed that body burdens for MDI substantially exceeded the UK guidance value in a number of workers.

The Solution

HSE looked at the correlation between airborne MDI and levels found in urine. This showed that the urine samples indicated substantially more MDI exposure than expected from the measured air levels.

In light of this, and the nature of the handling tasks within the process, it was suspected that skin exposure could be contributing to the overall body burden. The glove regime was reviewed and it was decided to replace the leather gloves with polyester gloves that had a polyurethane palm. These would provide chemical protection and, being cheaper, could be changed more frequently. The graph below shows individual worker results for both the leather and polyester gloves. In virtually all cases, use of polyester gloves reduced the exposure of the worker to below the guidance value.

The Outcome

Following the intervention, body burdens were significantly reduced, with all workers tested showing lower levels in urine. Whereas three-quarters of the workers exceeded the biological monitoring guidance value before the intervention, only a quarter still exceeded it afterwards, and then only marginally. The airborne levels of MDI remained similar after the intervention, indicating that dermal contact had been the primary source of exposure, as suspected.

A straightforward improvement in the glove regime markedly reduced worker exposure to a potent skin and respiratory sensitiser, thus reducing the likelihood of future ill-health.

With thanks to Aspen Environmental.