Expert: Mike Fulcher - 7/28/2006

Question
We have a site with a 10000 gal diesel tank.  When diesel is added on a hot day, the high level alarm on the secondary containment goes off.  The 2nd containment is filled with brine.  The service company says that the hot diesel causes the brine to expand which triggers the alarm.  I didn't think water expanded very much when warmed?  Is the service company pulling my leg?  

Answer
After going back through some old handbooks, it looks like the explanation you've been given is within reason.  Going from 4C to 60C will get you a 1.7% volume change in fresh water.  Since we're both engineers we can assume that fresh and salt behave roughly the same (and because I can't find numbers for salt water).  Since the cross-section of the tank doesn't change, this would result in a 1.7% increase in tank level in a cylindrical tank (2" per 10" of tank).  Without the specifics of your tank it's hard to say with certainty that this is a valid explanation, but unless it's causing you other problems I'd go with it.