You should have at least rinsed it good with water and filled it some with water before welding...
It's not the liquid gas that causes the explosion, it's the vapors...
I watched a house burn down 40 years ago because the guy was welding too close to his gas tank and it started a fire.... The whole house was a total loss... He lived in an unincorporated part of the city where they had no fire hydrants and the tanker fire trucks had to fill up from other areas of the city with hydrants to fight the fire... Needless to say, the fire had a 45 minute head start before the fire department could start spraying water on it...
Whenever a house in that neighborhood caught fire, the neighbors dig out their lawn chairs and watched them burn... There was nothing they could do to help... :popcorn:
The guy we so upset with himself for not thinking before he welded the near the tank, he said that he should have known better.... A 30 year old man was in tears watching his house burn down, regretting what he was going to tell his parents when they came home from out of town... :(
You were lucky...