Underground Propane Tank Accident Prevention: Installation & Response

In his article in BPN’s September 2025 issue titled “Virginia Jury Convicts Propane Service Manager of Manslaughter,” attorney David Schlee highlighted a disturbing legal case involving an underground 500-gallon propane tank home explosion in Sterling, Virginia. Schlee’s article made it more clear than ever that propane companies must ensure employees adhere to internal policies and procedures, tank manufacturer instructions and national, state and local codes. As owner of and instructor for Propane Training Services, I’ve had years of experience with underground tanks. The following article can serve as a guide on the topic of underground propane tank accident prevention based on my and others’ experience.

What to Do Before, During & After Tank Installation

To begin, soil boring tests before purchase and installation on commercial land can prevent future headaches and major costs. Are you familiar with the property’s history and any undisclosed waste, chemical saturation or past dumping of hazardous material? Reference any geographical maps for flood zones and potential saltwater incursion, chemical treatment and soil conditions.

Department of Transportation (DOT) cylinders or American Society of Mechanical Engineers (ASME) bulk tanks have no self-determined shelf life. Yes, DOT cylinders require periodic requalification and are allowed for aboveground use only, and underground ASME tanks must have cathodic protection; however, their life expectancy will be determined by the company performing the containers’ pre-preparation and installation. Per experts, 97% of the life of an underground tank is determined by the tank’s coating and the rest by cathodic protection. Regardless of ownership, out of sight should never be out of mind.

Once the underground installation is completed, it must be monitored. National Fire Protection Association (NFPA) 58 requires that all underground ASME tanks meet installation and cathodic protection codes and standards. Periodic pipe-to-soil tests must be conducted and documented. All parties should be made aware of the findings of the tests and appropriate actions implemented if necessary.

Maintaining the area under the tanks’ dome is of primary importance. Are all valves accessible? Does the relief valve have a protective cap in place? Are regulators protected from water submersion? Is there visible atmospheric corrosion that may indicate there could be serious galvanic corrosion? Are data plates intact and legible? Installers and drivers should do their best to keep dirt and debris out of the dome area. Sloping the tank for runoff can be greatly beneficial.

Employee Training Prevents Underground Tank Accidents

As is typical with most accidents, multiple factors often contribute to the occurrence of an incident. Employee training is the primary prevention method. Propane company owners, technicians, contractors and delivery drivers all need to understand how to assess whether an underground tank may be compromised and pose a safety hazard.

Bulk delivery drivers play a critical role in monitoring both above- and below-ground containers, regardless of brand name or ownership. Are they trained to identify code violations? Are they familiar with out-of-gas or interruption-of-service pressure testing requirements?

Responding to Underground Tank Leaks

After years of training first responders in Florida and beyond, the No. 1 complaint I hear from responders is that they often cannot identify the owner or fuel provider when responding to an underground tank leak. Metallic or plastic tags reflecting the provider’s name and contact number must be affixed to the tank valve or riser and are commonly available. Unfortunately, in my own experience, I have found this complaint to be true and valid. Decals are a poor identification substitute for underground tanks. If you are the current propane supplier, affix your ID tag nearest to the service valve. If you are no longer the fuel provider, remove it and advise the customer you have done so.

First responders and all parties must understand that propane has no shelf life. It is flammable regardless of age and will always present a hazard. Companies should frequently generate tank throughput reports and pay special attention to zero usage accounts of all types.

Reading Underground Tank Levels

An ASME tank’s fuel gauge (dial) should never be relied on or taken as an indication that the tank is completely empty. Is it possible that an inactive tank is reading the water level in the container? If a technician or driver can fully depress the liquid filler valve and the gauge is reading anything but zero, the gauge may be reading a water level.

If the tank is determined to be completely empty, gas should never be introduced until a pressure test of the tank is conducted. This pressure test will determine the integrity of the tank welds, seams, threads, openings and the entire containers’ surface. Refer to your company policy.

To perform the test, shut the tank service valve off to the structure. Install a 0- to 120-pound pressure block gauge and use a small cylinder and flexible hose to drift fill a small quantity of propane (vapor only) into the tank. Pressure should be, at minimum, 50 pounds or higher. Thoroughly soap check all tank valves, regulators and fittings. Conduct the pressure test over a period of 24 hours or per your company’s policy.

Record and document the test’s start and end time and the beginning and ending pressure. If you determine the tank is suitable for continued service, perform a cathodic protection pipe-to-soil test. This will ensure that the anode(s) are still functioning and providing sufficient corrosion protection. Replace the anode(s) if readings are low. Purge any air or nitrogen (if used) before filling.

What to Do in the Event of a Tank Leak

Should the gauge lose pressure, you can then assume the tank has been compromised and should be scheduled for removal. NFPA 58 provides steps in properly abandoning underground tanks on-site; however, I would check with your state or local authority having jurisdiction requirements.

For whatever purpose, if there is a delay in evacuating the tank, mechanical fill and service valve locks must be installed. Most use an easily available, inexpensive, “clamshell”-type locking mechanism or another type of fill valve restriction lock. Red tag the tank and update your database and delivery communications method accordingly.

Underground propane leaks, regardless of the source, always follow the path of least resistance and are not easily detectable. Soil and sand will scrub the odorant from the gas.

Where a concentration of gas is suspected or apparent (frost, dead vegetation, coal-black earth or insects), evacuate the structure immediately, removing people upwind and uphill. Extinguish all sources of ignition and do not operate any doorbells, light switches or garage door openers. Let the building air out naturally. Call 911. Consider notifying your utility to bring down the power to the structure. Protect lives, play defense.

A bar-prove leak survey on any underground tank or piping system must be performed with a combustible gas indicator. Test around the circumference of the tank, underground piping and near the foundation of the residence or building. Record any percentage of gas detected and actions taken to mitigate the leak.

Underground bulk tanks offer an element of safety, aesthetic benefits and many years of service. The ground temperature keeps the tank’s vapor pressure well below the relief valve setting, and in the event of a fire, in most cases, the fire travels over the dome with no consequences.

Regardless of ownership, an underground propane tank is a highly valuable energy storage asset and a long-term investment — and must be treated like one.