Welding Smoke and Sacramental Incense

[DRWeig]

I've had this posed to me half a dozen times in the past two months.

"Need a sensor to sense welding smoke to activate / deactivate exhaust fans"
"Need a sensor to sense incense smoke to activate / deactivate exhaust fans"

These things generally happen in large-volume rooms like an auto shop or church, so the smoke dissipates to a very low level by the time it rises to a place in which a sensor could be mounted.

I have suggested field trial-and-error with a VOC (volatile organic compound) sensor and/or a smoke detector with relay output like we use in ducts. I figured smoke is smoke, so a smoke detector might work if it is sensitive enough. But if not, perhaps a VOC sensor can grab the non-solid products of combustion or smoldering.

Fan needs to run a good bit after the welding / church service is over to clear it out. The time it takes to do so is in question.

Anybody have any better ideas?

Best to you,

Goober Dave

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[berkshire]

This might not work so well in a church, but have you considered source point capture devices?
B.E.

You are judged not by what you know, but by what you can do.

 

[SAK9]

Dr Weig,
Do not encourage such lazy behavior.It will take a while for the smoke to build up and reach a level that can be measured given the rather small generation rate and the large volume of the space.Any sensor will lose its sensitivity unless tested and maintained regularly and this would mean fan start getting delayed as time goes on .I do not have any faith in such lazy mob maintaining the sensor in good condition.
A welder is undertaking a dangerous task and turning the exhaust on should be part of the precautionary checks before he energises the rod.As for the church situation,I would try to locate the relief air grille over where the incense will be burnt.
If I really had to automate the fan start ,I would not trust anything other than an aspirating system like the VESDA.

 

[EnergyProfessional]

using a smoke sensor to activate the exhaust may also be in conflict with the fire elarm system. Especially whne the make-up air for that exhaust is transfer air from other spaces. in AHU we typically disable the AHU whne there is smoke sensed for that reason. you should tlak to the person who designed the fire elarm system who can tell you what the intent is.

 

[chicopee]

"...ducts. I figured smoke is smoke.." Well welding smoke and incense smoke are not the same. Welding smoke will have toxic properties much greater than those of incense smoke. Follow Berkshire's advice as a localized exhaust system will be much more effective. A related question: Does any body knows the reason for incense smoke being used?

 

[DRWeig]

Thanks all,

I agree with all of your comments, I'll be taking a different approach when this comes up again, as I'm sure it will. Sometimes building automation goes too far.

chicopee, in the Catholic church, the smoke is a symbol of purification and sanctification. It's just a symbolic ritual nowadays, but it used to be thought to chase away the evil spirits and demons. That's what I was taught anyways.

Best to you,

Goober Dave

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[Drazen]

in my area it is prescribed to have permanent ventilation at welding places, some good reasons for that are already stated in previous posts.

if target is to reduce energy consumption, the best path would be to localize exhaust as much as possible.

 

[IRstuff]

Is it possible to tie the fans to the actual operation of the welding equipment, i.e., gas flow? One benefit of this would be if the gas was on without actual combustion, the fans would turn on, regardless. Which would also potentially mitigate the case where the welder is alone, and is stricken, but the gas flow remains on.

TTFN
faq731-376

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[chicopee]

You are correct about the present purpose but the original purpose was to be used as a masking agent to the scent of decomposing dead human beings.

 

[DRWeig]

Yuck, chicopee!

THe latest client says the welding guys always turn on the fan, but they leave it on all day. They want to minimize ventilation for energy savings. They're going to put a delay-off timer on the fan and make the welders start the timer with a pushbutton as they quit welding for the day. He says it'll be a discipline thing, and they'll adjust the timer to a value that clears out all the smoke.

Best to you,

Goober Dave

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[berkshire]

DRWeig
Why don't you just stick in a relay for the fan, with a post weld delay timer . Set it to go on when the weld contactor is activated.
I know you cannot do that with a stick welder, but very few shops use stick these days. Of course having said that, yours will be one of the few shops that do.
B.E.

You are judged not by what you know, but by what you can do.

 

[SAK9]

Dr Weig,

What about a welding flame detector (aka light sensor,PE cell)to activate the fan?Coupled with a delay timer might do the job.

 

[DRWeig]

Thanks folks!

berkshire has the method they're going to employ on this one.

For the church incense, perhaps the same thing. They just want to clear out the smoke after the mass or other ceremony, but not leave the fan on all day (or all week).

Best to you,

Goober Dave

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[berkshire]

DRWeig (Electrical)
Dave, it sounds like your church could just use a rotary timer switch, of the type where you just set the desired run time.
B.E.

You are judged not by what you know, but by what you can do.

 

[DRWeig]

Thanks again berkshire,

A twist timer (or electronic equivalent) will do fine since the church services are generally of a known length of time.

The welders are a different bunch -- they may smoke for 2 hours or 8 hours, we never know.

Best to you,

Goober Dave

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[willard3]

+10 on a mark-timer switch on a local fan.

Neither of these functions needs to be automated.