Skin absorption of isocyanates: Laying of floor screeds
A company laying a polyurethane floor were using a resin mixture
containing a methylene diphenyl diisocyanate (MDI) based hardener.
The process involved one worker mixing the resin, another carrying
the resin to the application area and two workers spreading the
resin with trowels and smoothing with rollers.
The two floor spreaders were observed by occupational hygienists
from HSL to be wearing short-sleeved tops and general-purpose
gloves whereas the other two other workers wore long sleeved
Isocyanates are respiratory and skin sensitisers. They
have been identified by HSE as a major cause of asthma in the motor
vehicle industry and, under the COSHH regulations, there is a
responsibility on duty holders to reduce exposure to such
substances as far as is reasonably practicable.
Some hardeners and resins that are based on isocyanate polymers
have low volatility and therefore a low risk of inhalation
HSE investigated the potential for dermal exposure during the
laying of polyurethane floors.
What We Did
Personal air samples were taken for all workers and analysed by
scientists at HSL. Inhalation exposure (8hr Time Weighted Averages)
was low (all results well below the Workplace Exposure Limit) and
results agreed with static samples indicating no significant
aerosol exposure. MDI was detectable on glove samples from the
worker mixing the resin and one of the floor spreaders.
Pre and post-shift urine samples were collected over 4 days from
all workers and analysed by the biological monitoring team at HSL
for methylene dianiline (MDA), a biomarker for MDI exposure.
All samples had detectable MDA levels which were higher
pre-shift than post-shift indicating a delayed absorption route
which can be explained by dermal absorption. The levels of MDA
measured in urine were higher than those values expected from
inhalation exposure alone at the air concentrations measured.
Statistical analysis also showed a significant correlation
between MDI levels measured on gloves and next day pre-shift
urinary MDA levels.
Biological monitoring showed that dermal absorption of
isocyanates is possible and results can exceed the UK biological
monitoring guidance value of 1 µmol/mol creatinine
Evidence for significant dermal absorption of isocyanates has
been demonstrated and appropriate precautions when handling resins
containing isocyanates should be taken.
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