Little General Store Propane Explosion - US Chemical Safety and ...

Little General Store September 2008
4.0 Propane System Fundamentals
4.1 Propane Properties
Propane is used extensively as a fuel for cooking and heating in residential, retail, and commercial
applications. 20 It is a gas at ambient temperature and pressure but is transported and stored as a liquid.
Propane-air mixtures can be explosive when the atmospheric concentration of propane is between 2.4 and
9.5 percent by volume. Because propane is odorless and colorless, small quantities of an odorizing
chemical (ethyl mercaptan) are added so leaks can be detected by smell.
Unlike natural gas, propane is heavier than air. Consequently, propane releases tend to accumulate at
ground level or in other low points such as pits and basements.
4.2 System Features
The propane system at Little General consisted of a stationary 500-gallon storage tank (Figure 6) and two
supply regulators to reduce the pressure of the propane for pizza ovens used in the store. The storage tank
had five connections:
1. A fill connection fitted with an internal check valve;
2. A liquid level gage to measure the quantity of propane in the tank;
3. A relief valve (safety device) to prevent over-pressurization of the tank;
4. A service valve to supply gaseous propane to the regulators; and
22