Requirements and challenges
Our in house Technical Specialists & Occupational Hygienist investigated the issues.
A recently installed heater was found to be corroding rapidly, and the supplier had suggested that this could be due to dichloromethane vapour from a paint removal tank.
Halocarbons, a chemical group which includes dichloromethane, are known to break down at high temperatures, releasing hydrogen halide gases. These gases form acids such as hydrochloric acid when in contact with water, which can react with metals and deposit halide ions such as chloride, which are corrosion promoters.
Due to the large amount of powdered rust, it was possible to take a sample of several grammes and send it for analysis.
It was found that the rust contained 1.75mol% bromide but only 0.07% chloride, suggesting that a substance other than dichloromethane was causing the problem.
The only significant source of bromide in the Heliworks facility was a vapour degreasing tank which used 1-bromopropane.
Air monitoring using sorbent tubes showed that vapour concentrations in the air near the tank were 8ppm dichloromethane and 6ppm 1-bromopropane. The higher potency of the 1-bromopropane with regard to corrosion was thought to be due to the weaker bromine-carbon bond (bond energy 280 kJ/mol) compared with the chlorine-carbon bond (bond energy 330 kJ/mol), which means that it can form acids much more easily.
Further research showed that 1-bromopropane was an irritant and a neurotoxin, as well as a potential carcinogen and reproductive toxin. Some literature claims that loss of feeling in extremities can begin with continued exposure at concentrations as low as 1ppm. In contrast, suppliers of 1-bromopropane-based solvents maintain that concentrations of 100ppm are safe.