# How much pressure for gasses to explode?

1. Sep 3, 2015

### Jasper Denarius

I'm wondering about the amount of pressure required for natural gas (the kind pumped into homes for heating systems) to produce an explosion when exposed to an ignition source. Is there a formula of some sort to calculate this?

Specifically, if a town house (row home) were filled up with natural gas, say from a leak, about how much gas would need to leak into the home in order for the entire building to explode (not burn down, but explode), leaving no part of the structure intact? And how much pressure would this gas need to be under?

Would the amount of pressure normally provided by the home (as in the amount that regular oxygen-rich atmospheric air is under while in the home) be enough to cause this, or would some sort of additional containment be required to allow the gas to accumulate to such a degree?

I'm asking because this was an official story given for such an explosion that a friend of mine was affected by, but there were sketchy elements to the whole event, and I'm trying to figure some things out.

2. Sep 3, 2015

### SteamKing

Staff Emeritus
It's not a matter of pressure for creating the circumstances for a gas explosion, it's a matter of the concentration of the gas when mixed with the air inside the structure which is a critical variable.

Natural gas is composed primarily of methane plus some odorant in a small concentration. In order for methane gas to ignite, at normal atmospheric pressure, its concentration in air needs to be at least 4.4% by volume, with an upper limit of 15%-17%. If the concentration of methane is above or below these limits, no explosion will occur, even in the presence of an ignition source:

https://en.wikipedia.org/wiki/Flammability_limit

The ignition source also must be sufficiently energetic.

Of course, should the pressure be elevated for some reason, these limits may change. Unless this building were a pressure vessel of some sort, most residential structures are not designed to withstand large pressure differentials. Collapse of a structure can occur when as little as 2 psi over pressure is present (14 kPa).

https://en.wikipedia.org/wiki/Overpressure