HMN- It was another warm Saturday when Orlando Fire Department was dispatched to a gas leak. Engine 101 and Hazmat 1 responded with other Orlando Fire Units to a reported gas leak caused by construction. The first arriving unit, Engine 5, relayed that the leak was from an underground propane tank that was struck by an excavator (trackhoe). The homeowner advised that after the line was struck there was a high pressure release that lasted for approximately two minutes which then reduced to a minimal flow.
Firefighters approached the leak in full PPE and determined that the leak was from a half inch opening where the pressure relief valve has been sheared off. An inline expansion plug was inserted into the damaged valve body and soapy water spray confirmed that the leak had been stopped. The service valve threads were obviously damaged as was the pressure gauge preventing determination of remaining volume in the buried tank. The decision was made to mitigate the unknown remaining pressure with a propane flare kit to remove the remaining propane.
Once the flare-off operation had started, the top of the tank was exposed in an effort to determine the size of the tank and check for any other damage. The tank was approximately six feet long and two and a half feet in diameter which was calculated to be a 250 gallon tank. With a liquid to vapor expansion ratio of 1:270 a full tank was expected to yield 67,000 gallon of gaseous propane. Initial flare was adequate but slowed significantly after 45 minutes. It was believed that his was due to auto-refrigeration of the propane and being able to pull on vapor and not liquid due to valve configuration.
The decision was made to use the onsite excavator and operator to dig a trench next to the tank and expose an entire side. On the side of the tank that was exposed, it was possible to visualize a frost line at approximately 1/3 up the bottom of the tank. This allowed us to estimate that there was roughly 80 gallons of liquid propane remaining. Water was applied to the tank via a garden house in an effort to warm the liquid propane for faster evacuation resulting in a slight increase to the flare.
Constant evaluation indicated that the water spray on the tank was only minimally effective. Greater warming was needed to keep the tank from auto-refrigerating. Firefighters decided to flood the trench with tank water from Engine 101. For better results, Engine 101 recirculated the water within the pump to increase its temperature. Within 2 minutes, the results of the flooding were obvious as the flare was now operating at a much higher burn-off rate.
As the liquid volume of the tank decreased, the tank began to float in the trench. This allowed us to rotate the tank upside down, finally allowing for withdraw of liquid propane instead of vapor.
Once the tank neared empty, the excavator was used to lift the tank from the trench and place it at surface level in the front yard. While still connected to the flare kit, the inline plug was removed and water was injected into the tank using a garden hose. As water filled the tank, the remaining propane vapor was forced out to the flare. Once the product was completely evacuated, the tank valves were removed to allow for safe disposal by the home owner.
Total operation time was five hours before fire crews concluded operations.
Thanks to Lieutenant Derek Schaumann of E101/HM1 for his submission of this article and pictures.