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To: Bearcatbob who wrote (26767)	1/10/2004 1:03:10 PM
From: Tommaso	Respond to of 39344

>>E. - what makes H2 so dangerous is the explosive limits when mixed in air. <<<< I still recall the rain of broken glass from repeated explosions of improperly purged hydrogen generators in high school chemistry class. H2 is almost as dangerous as acetylene.

To: Bearcatbob who wrote (26767)	1/10/2004 3:33:41 PM
From: E. Charters	Read Replies (1) \| Respond to of 39344

Figures aren't everything. Behaviour is. All combustible gases mix with air and at certain ranges of mixing are explosive. The most dangerous gases are the heavier ones like propane that do not disperse well, being heavier than air. Light gases disperse easily, making methane and hydrogen safer as they 'goes up'. Of course they can get trapped in blind pockets there too, but generally in ventilated instructures it is safer. In mines methane poses a problem where ventilation is not pervasive. Hydrogen is not very explosive in concentrated form. It is not prone to sudden conflagration when pressure is violently released as propane and methane-butane are. Fires from hydrogen are less hazardous to be near as the gas evolves upwards so quickly the heat at the base and sides is minimal. This is why 26 people survived the Hindenburg fire, despite some being trapped underneath the wreckage. If you pierced a hydrogen tank with a bullet it would not explode. Not so a propane or methane tank. I would not want to be within 500 feet of a 100 lb propane tank that was pierced violently. It would not be a problem to be within 50 feet of such a hydrogen tank piercing. A large LPG tank has the danger of a small atom bomb. A large hydrogen tank is much almost innocuous to surrounding population. Where H2 is a problem is it leaks through fitting that are perfectly OK for propane. It is much harder to contain. This needs to be worked on. If carriers are developed other than iron chips, then H2 will be a good fuel for public transport and outlying stations at least. Right now you can get safe hydrogen for fuel cells out of borohydrates. In a sense the hydrogen economy is with us in the air expansion engine. It is just not very efficient now in that we are burning fuels at low efficiency. We are perhaps 1/2 as efficient as the steam age was. We need to get to fuel cells and more efficient engines. Sadi Carnot thought we could get to 70%. So far he has not been proved right. High time we worked on that. EC<:-}

To: Bearcatbob who wrote (26767)	1/10/2004 5:00:04 PM
From: hank2010	Read Replies (4) \| Respond to of 39344

So looking at your chart, Bob. Fuel Gas Air Lower Limits (%) Air Upper Limits (%) Methane 5,0 15,0 Ethane 3,0 12,4 Ethylene 2,7 36,0 Propane 2,8 9,5 Propylene 2,0 11,1 Butane 1,8 8,4 Carbon Monoxide 12,0 75,0 Hydrogen 4,0 75,0 Acetylene 2,2 80 Limits for fuel gas, air and oxygen at 20ºC and atmospheric pressure. Does this mean that at 2.2% air, the acetylene is explosive, at 2.8% air, propane is explosive, hydrogen and methane are not until it is 4% air for hydrogen and 5% for methane? And then when there is more than 9.5% for propane, or 15% for methane these gases are no longer explosive, whereas hydrogen and acetylene remain explosive until there is more than 75% and 80& air? TIA