Above ground tanks will need constant maintenance and the occasional reconstruction to make sure that it complies with industry standards. To prepare an API 653 tank for reconstruction, a qualified engineer will have to perform a gas-freeing procedure to drain the area of dangerous gas.
Tanks will often store products like oil and liquid fertilizers. These products can gas off and fill the tank with noxious fumes. The gas produced may become a toxic contaminant in the air, or be flammable; creating a massive fire hazard should it escape.
Gas freeing is a major requirement before tank reconstruction, according to the API 653 guidelines.
How Gas Freeing Works
Gas freeing is a common step to prepare tanks for cleaning and reconstruction. The goal is to reduce flammable and noxious gasses to one percent, while increasing the oxygen levels to about 21 percent.
Usually, the inspector can achieve this by purging the tanks using air. Blowers and vents ventilate the area and push fresh air into the tank. The gas is either collected or dispersed — the engineer carefully controls the exit of the gas to prevent others from inhaling it. It also minimizes the risk of the gas catching fire.
The Risks of Gas Freeing
Gas freeing is a requirement to give workers a safe environment while cleaning or reconstructing the tank. Unfortunately, the gas freeing procedure itself is extremely hazardous. One of the major problems is gas inhalation — inhaling gas from stored substances can be toxic and lead to all sorts of respiratory problems.
Some gasses can also be extremely flammable, which is why there should be absolutely no type of flame anywhere nearby. Smoking is strictly prohibited, and engineers involved in the operation must wear anti-static clothing to minimize the risk of producing sparks.
This is why only qualified personnel perform gas freeing operations — it is an extremely risky procedure. You will need it if you want to clean and reconstruct your tank.