This is the cross sectional view of the Omnisafe fitting at finger tight (click to enlarge).
The gap between the torque eliminators is the same as the gasket thickness (.028”). If the gasket is missing, the torque eliminators bottom out into a “fail safe” mode. This prevents torroid to torroid contact and destruction. The fitting cannot pass leak check with the gasket missing.
The legacy metal face seal fitting, if tightened without a gasket, will crush both torroids. The only remedy for this is to replace both glands. Cutting off and rewelding new glands is a particle generating, time consuming, and expensive remediation operation.
Tightening a legacy fitting without a gasket may even seal and give a false positive leak check reading. If a gas system is certified in this manner it may later develop a leak due to the damaged torroids. A leak that initiates when process gases are present is a much more dangerous situation especially if the gases are corrosive, toxic or pyrophoric.