Monitoring and control of ventilation in
fiberglass manufacturing
Gas monitoring in the fiberglass manufacturing industry must meet
two main needs:
To warn if harmful styrene reaches an
unhealthy toxic and explosive level
To ensure that the management of
ventilation is done in the best way, ie. for fresh air
requirements.
Styrene is a heavy explosive gas
with a flammable range from 1.1 to 8.0 vol%.
The density of the gas is 3.59. (Air = 1,0)
The detector should be mounted appr.
0.2 m above the floor.
Harmful Gas
In the fiberglass manufacturing industry employees are exposed to
styrene, which is both toxic as explosive (moreover, it can be
absorbed through the skin)
Hygiencic threshold limit:
Level value NGV 8h 20% LEL
Maximum value TGV 15min 50% LEL
In fiberglass lamination, for instance when
manufacturing fiberglass boats, styrene is used as a solvent.
Unlike paint shops, the intention is not that
the solvent should evaporate, since the final product should contain
as much styrene as possible.
Ship builders use styrene both when spraying and laminating locally.
When spraying, which normally takes place in boxes, the styrene
should be monitored.
One takes into account both the need to warn against intoxication
but also for the risk of explosion. It is therefore natural to use
two alarm levels.
The first one enters at 1/3 of the hygienic threshold limit value
and the second at 20% of the lower explosion limit (20% LEL), ie,
0.22 vol% (2200ppm).
ATEX explosionproof styrene
detectors
Address list
ATEX
Modbus
Datasheet
IP54
IP
Protection
Class
IP44,
Low cost
IP
Protection
Class
Compatible with different types of bus systems
Control centre with built-in styrene detector
Detector
Comb. gases
Manual
Control of ventilation
The utilization rate of the spray boxes varies, but demand
controlled ventilation normally saves a great deal of money.
Ventilation control is adjusted so that the ventilation is turned on
when the work shift begins.
There is a minimum flow, which is guaranteed by either the
restriction of the fresh air intake or adjustment of the ventilation
plant at minimum ventilation.
Minimum flow has been calculated based on the explosions risk (20%
LEL).
Staring the fibreglass syringe activates ventilation supply and
exhaust air flow automatically to a minimum (calculated on the basis
of 1/3 of the level value).
To lower concentrations in the air after the painting the airflow is
controlled by means of detectors in the gas monitoring system.
The gas monitoring plant measuring the levels at the workplace and
in the extractor channel takes priority over certain ventilation
controls and the fibreglass syringe:
If the concentration exceeds the first
alarm level (health risk) the workshop ventilation will run at
full power, regardless of whether the fibreglass syringe is on or
not.
If the concentration exceeds the upper
alarm level (explosion hazard) fiberglass flow to the syringe is
shut off while alarm is given.
Ventilation at this stage runs at full effect.
Control of the lamination of fiberglass
manufacturing based on monitoring of control levels.
If the concentration has dropped below the
preset lower level the control returns to its normal position.
For alarm and shut-off operation we recommend
so called two-detector alarms, ie at least two detectors have been
activated, or at least a two-minute delay if you want to obtain the
function with only one detector.
At the local lamination the detectors are placed hanging in the
working zone and in the extractor ducts.
The gas monitoring plant is designed for stepless control of
ventilation.
When the level value of 1 at any of the detectors exceeds the preset
control value the ventilation is started at reduced power and the
gas concentrations are mixed and neutralized in the space in
question.
The reduced power switches over to maximum power if the second value
level is exceeded in any of the detectors.
Staff Warning Alarm is obtained when two detectors at the same time
has come to an alarm value.
Ventilation can also be zone controlled so that the first alert
level is only activated where the detector is mounted.
Sensor choice
To monitor the styrene it is normally sufficient to use a common
carbon hydrogen detector, which reacts to all carbon hydrogen types
including smoke gases.
Instrument choice
In cases where the ventilation control is not via a DUC, a special
instrument is required.
The instrument should be positioned so that
the alarm and any readings can be easily read and preferably led to
a frequent and significant location (outside the lamination shop).
To cope with the monitoring and management
data the instrument should be equipped with two alarm levels (with
associated relays) and concentration readings.
