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Dina, I am the Utah County Fire Marshal, and am trying to find out a question that is in the 2003 International Fire code.
What is the volume of a 24-hour rainfall as determined by a 25-year storm?
Here is the reference in the fire code as it is written.
2704.2.2.4 Outdoor design. Secondary containment for outdoor storage areas shall be designed to contain a spill from the largest individual vessel. If the area is open to rainfall, secondary containment shall be designed to include the volume of a 24-hour rainfall as determined by a 25-year storm and provisions shall be made to drain accumulations of ground water and rainwater.
Thanks for any help you could assist me with,
Dennis C. Barker Utah County Fire Marshal ********************************************************
Wow, this one is a doozy!!!! After speaking with our Hydrologist Brian McInerney at the National Weather Service, he pointed us in the right direction.
If you take all of the storms that have rain in a 25 year period, it is the storm that is the one that is basically once every 25 years. You often hear us say "this is a once in a 100 year type of storm". Similar to that. The size of the storm only happens or usually only happens every 25 years.
If you were to plot on a graph with storms for 25 years, with rain on one axis and time on another, we can determine how much rain would be a once in a 25 year event. There's some links on the right here to help you and will send you over to the Hydrometeorological Designs Studies Center. There's a list of cities in Utah, not all of them, but there is a link for Provo in Utah county.
Using the graph and the data plot, it shows that the 24 hour volume of rainfall for a 25 year storm is about 2.5 inches of rain. This means, that according to your firecode, you need storage areas that can withstand 2.5 inches of rain in 24 hours.
For the Salt Lake Airport, the 24 hour volume of rainfall for a 25 year storm is 2.21 inches of rain. Hopefully this will help you out!
Answered by KSL Meteorologist Dina Freedman
