Case Studies : Build-up of Solvent Vapours

The Problem
A Shipping Company was generating high concentrations of solvent vapours in an enclosed environment.

Painting in any enclosed interval void for an extended period will result in a continuing increase in solvent vapours as the coating is applied. The assumption is often made that if enough ‘clean air’ is forced into the void the concentrations will be maintained at an acceptable level.

Exposure and background measurements showed an increase in vapour concentration of organic solvents to more than 40 times the published occupational limit in a very short space of time regardless of the volume of clean air forced into the void.

The Process – Painted Interval Voids
The Occupational Hygiene Unit proposed a negative pressure system. The required extract volume of air was calculated based on the rate of solvent vapour release. This was supplemented at the opposite end of the void by supply air, from a clean source, at a volume approximately 90 to 95% of the extract capacity.

The supply air provided enough air movement to counter any dead spaces within the void and the extraction removed the contaminated air at the desired rate.

Air monitoring demonstrated the effectiveness of the system, with concentrations significantly reduced.

Concerns were voiced at an early stage regarding the possible detrimental effects this would have on the finished quality of the coating. The only detectable differences were an improved drying rate and allowed an earlier post-application inspection.

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