Ask the Expert Question-and-Answer Archive

by Ron Joseph

May, 2003

Flushing Solvents in Fluid Hose of Spray Gun

Q. We have a thermal oxidizer at the end of our paint finishing line and need to know if we can clean our paint hoses by flushing solvent directly into the spray booth filters. We have a modern fully enclosed spray booth and very little, if any of the solvent can escape from the booth without going through the oxidizer.

A. You are in a catch-22 situation. If you flush the solvents through the booth they will be thermally oxidized by the abatement equipment and only a small fraction (perhaps 1-2% depending on the efficiency of your thermal oxidizer) will be emitted into the atmosphere. On the other hand, if you capture the solvents in a 55-gallon hazardous waste drum, you will be generating hazardous waste. Perhaps the better of the two evils is to incinerate the solvents in the thermal oxidizer since only about 1-2% will be emitted into the air. Another more environmentally friendly alternative is to capture the heptane and recycle it through a solvent distillation process that you can install in-house. Some people argue that this is considered to be "treatment of HZ", while others have successfully received permits to recycle the solvents via distillation.

If your facility is subject to the Aerospace NESHAP then according to the letter of the law you would be in violation for flushing the solvents into the spray booth, and you would be required to follow one of the four methods described in the rule. Similarly, if your spray booth or facility permit prohibits you from flushing the solvents into the filters, you will obviously be in violation if you do so. On the other hand, since you abate your VOCs you might be able to get a waiver to allow you to follow this practice.

Most companies do not have an abatement system, and therefore the practice you described is definitely a no-no for them. Even if a state agency does not have a rule prohibiting this practice, it is a bad for air quality.