Even my air compressors have blow off valves, did something get lost in the advancement of technology from the boiler days ???? it seems to be a pretty stupid design that doesn't have relief valves.
They have, the problem here was that the relief valves vented way too much gas - they're in the houses of people... and one spark with the right amount of oxygen and stuff goes kabooomm. Gas fires are no joke, gas explosions even less.