Yesterday, 11:59 PM
Using compressed air to evacuate fuel tanks can be effective but carries serious safety risks, especially with volatile fuels like gasoline or solvents. The method must be carefully controlled to avoid static discharge, vapor ignition, and unintended over-pressurization.
What Blowing Down Means
Blowing down a fuel tank refers to the process of applying low-pressure air to force fuel out of the tank into a container, typically for maintenance, repair, or disposal. This technique is often used when gravity draining is impractical, such as in boats or vehicles with inaccessible tank outlets.
Terminology Note
One operator successfully used a blow-down method on gasoline tanks by applying only a few psi of air through a rubber hose, gently pushing fuel into a jerry can. No fire or spill occurred. However, when preparing to do the same on a boat’s plastic tank, concerns arose due to the longer hose run and static potential.
Another technician recalled using a tennis ball with holes as a makeshift seal for diesel tank bleeding. Compressed air through the ball helped prime the system without over-pressurizing. Diesel, being less volatile than gasoline, poses lower ignition risk.
A story from Alberta involved a bulldozer operator accidentally rupturing a gasoline pipeline. The machine was drenched in fuel, but no fire occurred. Engineers later concluded that the vapor concentration was too rich to ignite—a rare but fortunate outcome.
Recommended Practices
Blowing down fuel tanks with compressed air can be done safely, but only with strict attention to vapor behavior, static control, and tank material. Gasoline and similar solvents pose significant risks due to their volatility and flammability. When in doubt, use inert gas purging or mechanical draining methods. The goal is always the same: remove fuel without introducing fire.
What Blowing Down Means
Blowing down a fuel tank refers to the process of applying low-pressure air to force fuel out of the tank into a container, typically for maintenance, repair, or disposal. This technique is often used when gravity draining is impractical, such as in boats or vehicles with inaccessible tank outlets.
Terminology Note
- RVP (Reid Vapor Pressure): A measure of a liquid’s volatility; higher RVP means more vapor formation at ambient temperature.
- Static Discharge: An electrical spark caused by friction or movement of air or fluid, which can ignite fuel vapors.
- Inert Gas Purging: Replacing oxygen-rich air in a tank with nitrogen or CO₂ to reduce fire risk.
- Fuel Vapor Envelope: The concentration of fuel vapor in the air surrounding a tank, which can be too rich or too lean to ignite.
- Blow Gun: A handheld air tool used to direct compressed air into a hose or fitting.
- Static electricity is the primary hazard when blowing down tanks. Air moving through plastic hoses or across plastic tank surfaces can generate a spark. This is especially dangerous with gasoline, which has a high RVP and forms explosive vapor-air mixtures.
- Oxygen introduction increases the risk of combustion. A sealed tank typically contains fuel vapor and minimal oxygen, making ignition unlikely. However, blowing air into the tank introduces oxygen, creating a flammable mixture if an ignition source is present.
- Container warnings on solvents like methyl ethyl ketone (MEK) often advise against pressurizing the container. MEK has similar volatility to gasoline, and the warning reflects the risk of rupture or ignition.
- Tank material matters. Metal tanks dissipate static better than plastic ones. Boats often use plastic tanks, which are more vulnerable to static buildup.
One operator successfully used a blow-down method on gasoline tanks by applying only a few psi of air through a rubber hose, gently pushing fuel into a jerry can. No fire or spill occurred. However, when preparing to do the same on a boat’s plastic tank, concerns arose due to the longer hose run and static potential.
Another technician recalled using a tennis ball with holes as a makeshift seal for diesel tank bleeding. Compressed air through the ball helped prime the system without over-pressurizing. Diesel, being less volatile than gasoline, poses lower ignition risk.
A story from Alberta involved a bulldozer operator accidentally rupturing a gasoline pipeline. The machine was drenched in fuel, but no fire occurred. Engineers later concluded that the vapor concentration was too rich to ignite—a rare but fortunate outcome.
Recommended Practices
- Use inert gas like nitrogen instead of air when blowing down gasoline tanks to eliminate oxygen.
- Ground all equipment and hoses to prevent static buildup.
- Limit air pressure to under 5 psi to avoid tank damage and excessive vaporization.
- Avoid using plastic hoses or fittings unless they are anti-static rated.
- Perform the procedure outdoors or in a well-ventilated area away from ignition sources.
Blowing down fuel tanks with compressed air can be done safely, but only with strict attention to vapor behavior, static control, and tank material. Gasoline and similar solvents pose significant risks due to their volatility and flammability. When in doubt, use inert gas purging or mechanical draining methods. The goal is always the same: remove fuel without introducing fire.
