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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