3 safety challenges for backup generators

Randy Warner wrote an excellent article about backup generators in the February 2024 issue of LP Gas. I intend to build on his article, emphasizing some safety issues I’ve seen.

My experience on the safety and state rules side of this goes back almost 30 years. Much has evolved since then. The rules we use have changed a little.

Storage capacity

The first situation came after a bad snow and ice storm. Well, bad for this area. A grocery store had a backup generator fueled by one 100-gallon propane cylinder. That the fuel ran out shortly after putting the generator into use was no surprise. I don’t know how much of the store ran off the generator. If it included the refrigeration units and all of the lighting, this was poor planning. If it was only the sales area, they might have reasonably expected a longer run. Likely it was somewhere in between.

The company owning the cylinder wouldn’t make a delivery, as it considered residential needs a higher priority. State law said no other company could deliver to this container. Proper planning for fuel capacity and running time based on desired service must be in your calculations.

Separation requirements

Propane is replacing diesel as the fuel of choice for many backup generators. Diesel supports algae growth, even inside the total darkness of the tanks. There can also be fuel stratification problems if the tank is not stirred. Propane solves these problems. The builders and installers of the new propane-powered backup generators initially didn’t account for some separation requirements, as described below.

Some of the initial generator sets were intended as models of compactness. The footprint of the units was kept small by stacking everything in a frame. A horizontal 100-gallon container was on the bottom with the generator right above it. That meant the relief-valve-to-source-of-ignition separation requirement was not met. They initially “solved” this by running a PVC pipe to a discharge point above the unit. That violated both the materials requirement and restrictive piping for a relief valve discharge found in section 6.9.2.13. I’m not sure if this has been properly solved.

Cellphone towers are “postage stamp” sized lots, sometimes with multiple users sharing the tight space. There were some installations where backup generators were so closely spaced that filling one of those containers while the neighboring generator was running violated separation requirements. Also, the neighboring generator could come on during a container fill, putting the employee at severe risk if they disconnected the fill hose. This was partially solved by adding section 6.29.3, allowing reduced separation requirements for the fill valve when the container was fitted with a fill valve with an integral manual shutoff valve.

Further, if all of the specifications in 6.29.4 are met at outdoor telecommunication facilities, additional separation distance requirements are relaxed. See the code for details. Separation requirements for regulators must also be considered, as Warner states. These requirements are not relaxed by 6.29.4.

Raised containers

Florida officials provided descriptions and photos of generator sets with large ASME tanks tens of feet off the ground at power substations. This may have been an effort to keep them above flood levels. NFPA 58, section 6.8.4.2, prohibits ASME containers of less than or equal to 4,000 gallons W.C. from being more than 3 ft. above grade unless the structure is insulated steel with a fire resistance rating of at least two hours.

By the way, this topic of raised containers at flood-prone locations is the subject of a task force on the National Propane Gas Association’s Technology Standards & Safety Committee. There are clear contradictions between the Federal Emergency Management Agency’s National Flood Insurance Program requirements and NFPA 58. There are no solutions to this conflict yet.

Richard Fredenburg is an LP gas engineer at the North Carolina Department of Agriculture and Consumer Services, Standards Division. He is also a member of NFPA’s Technical Committee on LP Gases. Reach him at 984-236-4752 or richard.fredenburg@ncagr.gov.

NOTE: The opinions and viewpoints expressed herein are solely the author’s and should in no way be interpreted as those of LP Gas magazine or any of its staff members.

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