Michael Dresdner

Q: I have a room off my shop that I want to set up as a spray room. I only use shellac and spray it. Is shellac highly explosive when sprayed?
A: Explosion potential is measured by LEL and UEL, or lower explosive limit and upper explosive limit, a measure of the amount of any solvent gas in air. To understand LEL, think of how a carburetor works; you don’t get combustion if there is too much air and not enough fuel, or if there is too much fuel and not enough oxygen. To answer your direct question, the LEL of ethyl alcohol (that’s what’s in denatured alcohol and most shellac) is 3.3 % by volume. Shellac resin itself is not explosive or flammable separate from the solvent, so its presence makes explosion less likely, not more. In short, if you evacuate the air by having a fan blowing out the entire time you are spraying, turning it on before you spray and off after the air is clear, and have clean air coming into the room, you are not in any danger of an explosion in the room, since you are highly unlikely to ever reach the LEL.

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This entry was posted on Wednesday, November 25th, 2009 at 9:00 am and is filed under fire safety, shellac, spray. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.