exhaust inlet requirement for garages
exhaust inlet requirement for garages
(OP)
typically I see designs that require garage exhaust to be taken not higher than 18" above floor. I believe the reasoning is CO is lighter and with such low intake of the exhaust air we capture CO better. I wanted to verify the exact requirement, but can't find a code that details the 18"? I only found it referenced for fuel dispensing facilities in IMC 502.1.2, which is not my case. Many people tell me about the 18", but no one can show me the code.
some questions I have are:
- do diesel garages have the same requirement (they produce more soot and NOx than CO)
- assuming the 18" requirement is real, how are angled intakes treated? To increase the screened area, we typically have 45° sloped intakes. teh back (at wall being lower, the front being higher. now which do we measure to satisfy the 18"requirement?
some questions I have are:
- do diesel garages have the same requirement (they produce more soot and NOx than CO)
- assuming the 18" requirement is real, how are angled intakes treated? To increase the screened area, we typically have 45° sloped intakes. teh back (at wall being lower, the front being higher. now which do we measure to satisfy the 18"requirement?





RE: exhaust inlet requirement for garages
RE: exhaust inlet requirement for garages
RE: exhaust inlet requirement for garages
RE: exhaust inlet requirement for garages
RE: exhaust inlet requirement for garages
http://www.nfpa.org/codes-and-standards
RE: exhaust inlet requirement for garages
you are talking about CO not about C or O itself, and CO does not dissolve to C and O in the garage, also the garage has one or two exhaust outlets not an outlet near every engine.
also when Co spread in the garage it take all the garage volume as Dalton law, in a garage we are talking about concentration not volume, some codes ask to install CO or No sensor at certain heights from 9 feet and above, not at 18"
are you sure about 18" or it is 180"?
RE: exhaust inlet requirement for garages
Molecular weights:
CO = (1) Carbon @ 12 + (1) Oxygen @ 16 = 28
N2 = (2) Nitrogen @ 14 = 28
Mixed air = 28.966 http://www.engineeringtoolbox.com/molecular-mass-a...
This means CO will basically mix evenly throughout the space.
I've always understood that the low level exhaust was because tailpipes are low. Codes I've had to follow before required 50% low level and 50% high level.
RE: exhaust inlet requirement for garages
I think the intake height is more related to typical vehicle exhaust location and to take care of possible oil/fule spills?
Compositepro: thanks for the hint, i didn't know they are free. i got mine from the fire department. anyway, 88A (Garage) and 88B (Repair Garage) don't seem to mention anything. I know NEC requires 12"in Div-1 locations, but this is a garage only. any idea which ones would explain/require the intake height?
My design is to exhaust from low above floor and supply makeup air up high to flush out evenly. but some design I see and people i talked to (and no, no one could tell me what code exactly!) indicate it has to be taken from floor level and from above. so I'm still looking for some code reference.
I'm in WI, which references and amends IMC. not all NFPA apply, only the ones referenced in IFC.
RE: exhaust inlet requirement for garages
I also re-read NFPA 88A and 6.3 only seems to refer to cfm/ft² required (per our fire department NFPA 88A is not required, we follow IFC).
IFC doesn't seem to have specific vehicle garage requirements.
am I making this just too complicated if I don't have specific liquids or gases? Is it really (per code) just up t my judgment? I guess that is fine, just didn't want to walk into a trap....
RE: exhaust inlet requirement for garages
Vehicle exhaust usually connected to a pipe the end up outside without fan or any thing, this pipe is not considered as an exhaust system of the garage
RE: exhaust inlet requirement for garages
Best to you,
Goober Dave
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RE: exhaust inlet requirement for garages
DRWeig: good data, thanks. Do you have any such data on NOx or diesel soot? Assuming it is warm as well, it probably will do the same thing.
RE: exhaust inlet requirement for garages
Best to you,
Goober Dave
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RE: exhaust inlet requirement for garages
It probably has more to do with the fact, that installing sensors low and int he center of a garage in a clear span construction is a challenge. May be better if you have multiple columns, but in this cas there are none.
Either way, all seems to indicate taking all the dirt in at floor level is the best strategy. Especially with the makeup air unit discharging in high height. Taking air from high would mean all the clean OA just clears out the area in high height, where humans are not.
Thanks for all the comments.