The Client

Isocyanates are a primary component of moisture cure polyurea (MCU) products.

When an organisation intended to apply MCU coating products using specialised spray equipment they wanted to ensure that the risk of their workers to isocyanate exposure was adequately controlled.

The Problem

HSE has identified workers' exposure to isocyanates as one of the UK's leading causes of occupational asthma. Isocyanates are respiratory sensitizers and exposure has to be controlled to as low as reasonably practicable. In Great Britain a workplace exposure limit (WEL) has been assigned (20 µg/m³, 8-hour time weighed average).

MCU coating products are formulated with a range of polymeric isocyanates and some also contain high levels (>50%) of a powdered metal to provide anticorrosion properties. Although polymeric isocyanates are less volatile than monomeric isocyanates, significant airborne levels can still be generated depending on the application method.  Consequently measuring exposure can be challenging particularly as current biological monitoring methods only measure monomeric isocyanate and material safety data sheets may only identify polymeric species generically. Underestimates of isocyanate exposure are possible.

What We Did

In discussion with the client, we agreed a phased programme of work to ensure that they would have the relevant information to carry out a thorough risk assessment for application of the new proposed coating.

Firstly, our analytical team analysed four different MCU coating products. Two contained high levels of a metallic powder, which was found to interfere with the analysis, so a method was successfully developed to remove interferences. The safety data sheets only provided generic information about the isocyanate present within each sample. MDHS 25/4 methods were therefore used to characterise the specific polymeric species within the bulk samples. Confirmation that all the isocyanate (as the chemical group -NCO) was accounted for was determined by titration.

Secondly, following successful characterisation of the bulks, a spray booth was set up to model the clients spray application under controlled conditions, to evaluate likely exposures. The clients specialised spray equipment was used under their guidance to make the scenario as representative of real world conditions as possible.

 

Outcome/Benefits

For each of the four MCU products tested, airborne isocyanate was measured at levels in excess of the WEL. A significant health risk was identified not only for personal carrying out the spraying but also for those close by.

As we used the client's own spray equipment and worked closely with them to ensure the appropriate application scenario was used, our client was confident that our measurements provided an accurate assessment.

The client was able to review their risk assessment, consider exposure controls and assess the practicalities of the application of the MCU products to ensure compliance with regulation and to protect the health of their workforce.

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