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     Updated: 13 Nov 2018



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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).


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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.

Information on LEL och explosion hazard



E-mail: ewert@automatikprodukter.se     

Phone: +46(0)31-287202

Mobile: +46(0)708885298



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