BIX 015 - Refillable Gas Tank - StandardStandard Gas Tank. Safety Note Gas is a dangerous fuel if basic safety precautions are not followed. The filling of gas tanks should NOT take place in an enclosed space, always refill in the open air. Low pressure gas should be used i. e. Butane or a Butane Propane mix. Each tank carries a test certificate stating the test pressure and the butane propane mix ratio. 70 30. The filling of the tank is accomplished in the same way that a cigarette lighter