NO2 Sensor Placement in Fire House 2

[DRWeig]

Hi group,

Not exactly a thermo problem, but I haven't gotten any responses in the other forum I tried.

The situation is a fire truck with its engine running in its bay in the fire station. The client would like a sensor with alarming on high NO2 level (2 ppm) in case of exhaust leakage.

When the exhaust first comes out, it's hot and rises -- but NO2 is much heavier than air, so it falls when it cools.

Earliest warning would be a sensor up high, but what is the shape of the plume and how much does it diffuse? Could I even sense NO2 with a 0-10 ppm sensor?

A sensor down low by the floor, where a worker on a creeper may be exposed, would be later but perhaps more certain placement?

Oh, and sometimes they run the main building exhaust and leave the roll-up doors open instead of piping the exhaust outdoors...

Thoughts would be appreciated!

Best to you,

Goober Dave

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[Dougt115]

The plume going up would not be my first issue as it should not be dense enough to harm anyone. Look for where it will accumulate. Low areas, areas with poor circulation, ei. offices with open doors or windows nearby, storage rooms or corners.

The openness of the fire stations that I have seen (on open house days or school tours with my sons) lead me to think anywhere near the exhaust area of the truck would be good enough. The truck bays were large and open and would take a very extended amount of time to accumulate.

 

[DRWeig]

Thank you Dougt115, I did not consider the effect on sensing of the lower-density warm gas. I believe your thoughts are valid. I'm going to see if I can do some testing at the fire house later in the summer.

Best to you,

Goober Dave

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[dcasto]

I have to ask why you don't just look for CO as by the time you going a few ppm NO2, the CO is seven hundred times higher and easy to detect.at higher levels

 

[DRWeig]

Thanks dcasto,

Client says NO2 reaches toxic level more quickly than CO in diesel engine exhaust. I'm not able to debate him with my level of combustion knowledge -- I just have to sense what the spec says. I'd like to side with you, CO mixes nicely in the air.

Best to you,

Goober Dave

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[Compositepro]

At ppm levels the density of the gas makes no difference to mixing.

 

[dcasto]

I looked up the composition of diesel exhaust here. The CO is way higher. Then add in that NO2 is a small fraction of the total NOx

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1531320/?page=5

I looked up the costs, the no2 detect is way more expensive.

 

[Dougt115]

It may very well be a government regulation, there is no option but to comply. But I would agree with you about the CO. Maybe the CO device can be thrown in as a bonus or a two feature detector?

 

[DRWeig]

I think y'all have put me on the right track. The client's insisting on NO2 but I can easily bend him into including CO as well.

Best to you,

Goober Dave

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