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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