Abstract
Currently, about 75% of Finnish reinforced polyester
lamination workers are exposed to styrene concentrations
exceeding the current occupational exposure limit of 20
ppm. Several measures have been proposed to control
styrene exposure, but only a few of them are capable of
keeping the styrene concentration below 20 ppm. The
present study was carried out to evaluate current
ventilation systems in reinforced plastic plants and to
develop new, effective ventilation systems for
controlling styrene exposure. The roles of
styrene-suppressed resin and styrene emission during
different phases of the moulding process were also
studied.
Styrene exposure and the performance of current
ventilation systems were measured in 17 reinforced
plastics plants. Better styrene control was sought
experimentally by investigating the effects of
unidirectional airflow on a worker's exposure, by testing
local exhaust and local air supply ventilation methods in
controlling laminator's exposure and by examining the
possibilities to improve local ventilation using an
automatically moving ventilation unit. The
characteristics of styrene emission during hand lay-up
and the effect of a rolled area on styrene evaporation
were also determined.
Dilution ventilation systems are common in Finnish
reinforced plastics plants. In many cases, the
ventilation system was incorrectly dimensioned and
workers were exposed to high styrene concentrations. High
dilution airflow rates, over 850 m3 kg-1, may be needed
before a concentration level below 20 ppm is achieved
with the resin consumption rates common today. In order
to meet the present exposure limit, local ventilation
techniques should be used in combination with other
control measures.
Well-designed zonal ventilation methods (e.g., a
horizontal airflow tunnel) produced a favourable airflow
pattern for controlling styrene vapours in the lamination
area. However, work practices must be synchronized with
the airflow pattern before low styrene exposure levels
are reached. A worker standing in a unidirectional
airflow facing downstream may also receive significant
exposure due to contaminant transporting eddies formed
downstream of the body. It is possible to control this
type of exposure with a local air supply unit located
over the worker.
Styrene control during hand lay-up moulding is also
possible with the use of several local exhaust hoods. It
was estimated that adequate styrene control can be
achieved when the control velocity at the edge of the
mould is 0.15-0.2 m s-1 and the exhaust airflow rate per
laminate area is between 0.1 and 0.2 m3 s-1 m-2,
depending on the shape of the mould. An automatically
moving local ventilation unit, equipped with local
exhaust and a local air supply, was able to keep the
styrene concentration near or below 20 ppm when
medium-size products were laminated with the hand lay-up
method. A styrene concentration of below 20 ppm was also
obtained when a new type of spray booth, equipped with
automatically moving curtains, was used and when the
control velocity was at least 0.3 m s-1 during the
spray-up of gelcoat resin.
The use of vapour-suppressed resin reduced the total
styrene emission by 30-60%, but the reduction was much
lower during active lamination. After rolling, the
emission from the vapour-suppressed resin was found to be
very low, and, therefore, the emission rate was dependent
on the size of the surface area rolled simultaneously.
The use of these resins is beneficial, especially when
large products are laminated.
Original language | English |
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Qualification | Doctor Degree |
Awarding Institution |
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Supervisors/Advisors |
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Award date | 29 Aug 1998 |
Place of Publication | Espoo |
Publisher | |
Print ISBNs | 951-38-5250-4 |
Electronic ISBNs | 951-38-5251-2 |
Publication status | Published - 1998 |
MoE publication type | G5 Doctoral dissertation (article) |
Keywords
- occupational safety
- occupational health
- plastics industry
- indoor air
- styrene
- air quality
- ventilation (air conditioning)
- local ventilation