The design and installation of gas piping systems in homes and commercial buildings is guided by a set of regulations called NFPA 54 — the National Fuel Gas Code. The code, which establishes minimum safety requirements, is also used by forensic engineers to evaluate an explosion to determine cause and responsibility.
I once investigated a case involving a gas explosion in a retail business. To determine who held responsibility for the explosion, I first considered the chain of events that led up to the incident.
The business’ gas had been shut off in order for a gas appliance to be removed. After that work was completed, the town’s gas department turned on the gas to the store at 3 o’clock in the afternoon. However, the gas line had not been capped after the appliance removal so gas flowed freely into the building. The following morning, the store owner arrived and tried to light a gas heater inside the building. The resulting explosion killed the store owner, seriously injured a customer, and caused significant property damage.
I turned to the code to establish how the dangerous situation developed:
Section 3.8.2 states: Cap All Outlets.
(a) Each outlet, including a valve or cock outlet, shall be closed gastight with a threaded plug or cap immediately after installation and shall be left closed until the gas utilization equipment is connected thereto. When equipment is disconnected from an outlet and the outlet is not to be used again immediately, it shall be closed gastight.
The oversight of not capping the gas line during the appliance removal allowed gas to flow freely into the building overnight. The uncapped gas line was a code violation and a cause of this explosion. Whoever did not cap the valve was responsible. But there was more to this case.
Through NFPA 54, I was also able to establish an additional cause of the explosion: the gas employees. The code includes a System Equipment and Leakage Test that should have been performed by the gas department employees as part of their duties:
Section 4.2.1 states: Before Turning Gas On
Before gas is introduced into a system of new gas piping, or back into an existing system after being shut off, the entire system shall be inspected to determine that there are no open fittings or ends and that all manual valves at outlets on equipment are closed and all unused valves at outlets are closed and plugged or capped.
Section 4.2.2 states: Test for Leakage
Immediately after turning on the gas, the piping system shall be tested to ascertain that no gas is leaking.
If leakage is indicated, the gas supply shall be shut off until the necessary repairs have been made.
The gas department employees, I concluded, did not conduct an inspection of the property to identity potential leakage. Had they done so, the workers would have discovered the uncapped supply line. By applying the NFPA 54 guidelines, I determined failure to cap the line and inspect for leakage as two causes of the explosion. Furthermore, I placed responsibility with whoever removed the appliance and failed to cap the line and the gas department for failing to inspect the property, both critical safety practices.
NFPA 54 regulations exist to protect people and property. When the code is violated, the results, as in this case, are often catastrophic. After an event, these regulations are a valuable tool for the evaluation of cause and responsibility in an explosion.
Jeffery H. Warren, PhD, PE, CSP, is the chief engineer and CEO at Warren specializing in mechanical, machine design, and safety. His deep expertise in machine design and safety analysis makes him a frequent presenter, trainer and expert witness. In addition to investigating more than 2000 claims involving property damage and injuries related to machinery and equipment since 1987, Jeff has an undergraduate degree in Mechanical Engineering from the University of North Carolina as well as a Master of Science and a Doctorate in Mechanical Engineering from Virginia Polytechnic Institute and State University — both with machine design emphasis.