Pressure of Hydrogen air explosion
Pressure of Hydrogen air explosion
(OP)
Hi
I am a physical security consultant, i have a client who is concerned about a hydrogen / air explosion in his factory. I would like to know the pressures that could be attained using the following scenario
room size - 40m3
explosive - equivalent to 5kg TNT (is that possible for calculations)
what would pressure and impulse be on the walls of the room?
I am a physical security consultant, i have a client who is concerned about a hydrogen / air explosion in his factory. I would like to know the pressures that could be attained using the following scenario
room size - 40m3
explosive - equivalent to 5kg TNT (is that possible for calculations)
what would pressure and impulse be on the walls of the room?





RE: Pressure of Hydrogen air explosion
RE: Pressure of Hydrogen air explosion
Overpressure (psi) Expected Damage
0.50-1.0 Windows usually shattered.
1.0-8.0 Range for slight to serious injuries from flying glass and other missiles.
2.0 Partial collapse of walls and roofs of houses.
2.4-12.2 Range for 1-90% eardrum rupture among exposed populations.
5.0 Wooden utility poles snapped.
5.0-7.0 Nearly complete destruction of houses.
7.0 Loaded train cars overturned.
10.0 Probable total building destruction.
14.5-29.0 Range for 1-99% fatalities among exposed populations due to direct blast effects.
RE: Pressure of Hydrogen air explosion
RE: Pressure of Hydrogen air explosion
Regards
StoneCold
RE: Pressure of Hydrogen air explosion
We have a 40 m3 room= 1.3 kg/m3 (density of air)*40 m3=52 kg of air. The LEL of hydrogen is 40000 ppm (weight)=0.04*52=2.08 kg. of hydrogen in leaks will reach the LEL.
The combustion heat of hydrogen is 33 859 kcal/kg, so 2.08 kg will produce 70426.72 kcal.
The combustion heat of TNT is 1080 kcal, so 2.08 kg of hydrogen are equal to 65.21 kg of TNT and 1 kg of TNT produces 0.73 m3 of gas, then 2.08 kg of hydrogen will produce 47.6 m3 of gas.
In a room of 40 m3, the pressure will increase by double, so the wave pressure will be 15 psi.
But if you review the table of wave overpressures, is necessary only 8 psi to destroy the building.
RE: Pressure of Hydrogen air explosion
The peak pressures in a high explosive detonations are on the order of a million psi (at zero distance). As I said earlier, the peak pressure in a fuel-air deflagration is about 150 psi.
RE: Pressure of Hydrogen air explosion
You are right, a deflagration will produce, in a closed system, a maximum of 10 times the initial pressure.
Like you say a peak or maximum pressure could be 150 psi in atmospheric initial conditions. I said, overpressure waves 150 psi or 15 psi, twice are dangerous.
According to EPA tables, from 8 psi and more, the damages will be catastrophic.
Regards.
RE: Pressure of Hydrogen air explosion
Careful! Your concepts are flawed.
The use of ppm in the context of gases means parts per million - a concentration by volume - not a concentration by weight.
40,000ppm = 4%.
4% of a 40m3 volume of gas air/hydrogen mixture = 1.6m3 of hydrogen.
1.6m3 x 0.08375kg/m3 (mass of H2 at NTP) = 0.134kg of H2
Also, there is a difference in the lower flammable level and lower explosive level (LEL) for hydrogen. A hydrogen air mixture explosion is most powerful at a stoichiometric mixture ~30% H2.
RE: Pressure of Hydrogen air explosion
my own limited experience is that hydrogen generally goes off as a burning process (significant and distructive in its own right) and is difficult to get it to detonate except in very special circumstances.
you really need a specialist to answer you questions, good luck