So what’s the bottom line; is using an inert gas safer than using compressed air when testing an EVAP system with a smoke machine?

Of course inert gas is safer!  But you don’t have to take our word for it.
See SAE International Technical Papers on potential hazards when using air: and

See EPA’s EVAP Technical Guidance document (page 29) requiring nitrogen or other inert gas.

Think about it; the hazards of using air has absolutely nothing to do with the equipment you are using, or whether the equipment creates smoke or not, or whether the smoke vapor is created using a heater or not.  It has everything to do with introducing oxygen into the fuel tank system of a motor vehicle.

It is a fact, and independent studies published by SAE demonstrate, that it only takes 12% of oxygen volume in a vehicle’s fuel tank to support combustion!  Fuel tanks are normally too rich to burn.  In other words, the little oxygen that enters the fuel tank, under normal driving conditions, is not enough to create a flammable mixture inside the tank.  But SAE shows that it only takes between 1-5 minutes to create a flammable fuel mixture inside the vehicle’s fuel tank when using compressed air, which contains 21% oxygen.

Studies conclude that when using smoke vapor for leak detection, the best way to prevent creating a flammable fuel mixture inside the fuel tank is to use an inert gas to deliver the smoke vapor to the fuel tank.

* That is why virtually all auto manufacturers that use smoke technology require the use of nitrogen when testing the vehicle’s EVAP system with smoke vapor. 

* EPA in their “IM240 & EVAP Technical Guidance” document for years has required the use of an inert gas when pressurizing the evaporative system. And those instructions have nothing to do with a smoke machine, it only dictates the gas source to be used whenever pressure testing the EVAP system.

* The California BAR and CARB requires the LPFET Certified equipment use nitrogen when pressure testing the EVAP system.  

Adopt safer testing habits and procedures, especially when you are testing a volatile system like an EVAP system.  And we suggest you use equipment specifically designed for these safer test methods.

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