explosion venting 1

[bsrd]

Need some help in sizing the required area for explosion venting per NFPA national fire protection agency section 911. apparently the vent area is to be sized based on the room being designed for 100 psf outward pressure.

 

[ishvaaag]

For comparison, according to the spanish CTE at gas boiler rooms a weak (ejectable by the explosion) surface of

Surface (m2)=Volume (in m3) / 100
and not less than 1 m2

For example, a boiler room of 300 m3 would need 3 m2 of surface easily ejectable by the explosion.

Ventilation section needs not to be as much.

Source is RITE 2007 IT 1.3.4.1.2.3, in the code that by reference in CTE rules mechanical services design.

 

[BSE05]

I have done a few of these. I believe NFPA has an example in their deflagration venting section ( I don't think it is 911) I have always use 100 psf for resisting panels and 20 psf for relieving. The expample uses hydrogen, I believe, which is about the lowest flash point you can have. the example solves for the relieving area required.

Watch out for the prefab sheds. I have been blind sided before by these after submitting my (expensive) design. They never say so but they are designed to self destruct in my opinion. their relieving panels are extremely small in area. NFPA does have some language on self destructing storage.

 

[bsrd]

Thanks SteelyLee,

Section 911 is in the International Fire Code my mistake. It's NFPA 68 the has the deflagration venting. I've designed some also but was always given the area, I never had to determine the area. Is it a function of the material stored?

 

[BSE05]

Yes, the blast depends on the LEL, or lower explosive limit of the material stored. Look in the appendix for an area calculation using hydrogen or a similar gas with a very low ratio of gas to air. This would be a worst case scenario.

The need for venting depends on how much of what class of flammable liquid or gas. Have you gone through this analysis yet?

To go further than this you need to be a chemist.