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Direct Fired Make Up Air without Exhaust Fans 1

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goodwrench1

goodwrench1

Automotive
Jan 28, 2010
3
Hello,

I would like to ask the opinion of some experts in HVAC of an issue I am trying to get resolved at work involving air quality and safety, and would like to know what some of your thoughts are on the following.

I am an automotive mechanic for a delivery company and the building I work in houses just under 200 vehicles. These vehicles are moved throughout my shift in the building with the doors closed, and the exhaust fans electrically locked out. I have been told by plant engineering management that our "Rapid 4000 AM" model (Rapid Engineering) Direct Fired Heating units provide enough air flow without running exhaust fans, and if the air is bad to simply crack a pedestrian door open and the unit will compensate and push the toxins out the door. I know the units do have the capability to go into "flush" mode where 1 unit brings in 100% outside air and the other 1 goes into exhaust mode. There are 6 sensors to detect fumes that would put it into this mode, and only 2 are of the dual sensing (CO & NO2) variety. The other 4 are CO only, and the majority of our vehicles are diesel engines. We have never witnessed an alarm indicator to put it into flush mode even when the air seems unbreathable.

Many coworkers have had respiratory and sinus issues, including myself recently.

1.) I guess my question is it good practice not to run the roof exhaust fans in this type of environment?

2.) Shouldn't ALL the sensors be able to detect diesel fume toxins?

3.) How can you get the adequate air changes per hour if there are no exhaust fans running, no pressure relief ports, and no doors open?

4.) Is it bad practice to try to exhaust the fumes through my breathable air space?

I'm not sure if the fumes would violate OSHA rules because over a whole work shift they are probably diluted enough not to be in violation, but in my opinion they should be power exhausted, not pushed out the "nooks, crannies, & crevices" of the building. Also, they would probably change their habits if the were monitored for a short time by OSHA.

Thanks in advance to anyone who has some insight for me.
 
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Goodwrench,

Get a copy of the mechanical building code that's enforced in your location. It'll have minimum required exhaust rates for your occupancy -- plus the controls required.

The latest International Mechanical Code requires exhaust to run when occupied in an enclosed garage -- but may be cycled based on gas sensor input when unoccupied. Gotta put occupancy sensors in there too.

I'll paraphrase IMC 404.1 -- Enclosed Parking Garages. Mechanical ventilation systems shall be permitted to operate intermittently based upon detection of vehicle operation or the presence of occupants by approved automatic detection devices.

And yes, if you're using gas sensors to control exhaust, they all need to be able to sense both gasoline and diesel exhaust if both types of vehicle are present.

Let us know what you find out!

Goober Dave
 
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One more point -- sensing CO and NO2 is great to control toxins, but our noses are waaaaaaay more sensitive than those sensors. Diesel exhaust stinks, even when it's safe to breathe, and it's full of particulates that can irritate people who breathe them. Some are more sensitive than others.

Airflow should be arranged to have people in the fresh air stream, with all exhaust leaving through a non-occupied path.

It's about impossible to sense the odor with a sensor. You could try a wide-spectrum VOC sensor and crank up the gain on it maybe (have implemented this at a couple of hospitals where the fresh air intake was near a helipad). Doesn't work all the time, but improves the situation.

Again, be sure and post us with your solution!

Good on ya,

Goober Dave
 
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Goodwrench1,

The mechanical code will say to exhaust 1 or 1.5 cfm/ft2 but doesn't apply to your exact application... Let me try to answer your questions directly:

FIRST: Direct fired heating units' make-up air is designed to serve the combustion of the units, not the people in the space. That would likely not count toward any ventilation standard.

Your numbered questions:

1) Yes, absolutely.

2) Too hard. These are PAHs (polycyclic aromatic hydrocarbons). Detection points are low and odor thresholds are lower.

3) You can't. Your application needs a substantial air exchange rate; if control systems are relying on sensors that do not pick up the full story to exchange the amount of air needed, there is a problem.

4) Yes, of course.

CB
 
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Also, you say roof fans... the fans should be ducted down to exhaust from low level. This is the case for enclosed carparks, so I assume for your set up too.

 
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Thank you for the responses thus far. It may take a bit for this to shake and settle out at my employer, but I will say, once it is proven that the systems and practices being employed at my location are poor and unhygienic, there may be widespread implications nationwide as I believe this isn't the only facility that does not employ exhaust fans.

I think it's best that I emphasize to the management that these exhaust fans need to run whenever diesel vehicles are present because from what I've been researching there are other dangerous gases present besides CO & NO2. Even if those contaminants are within safe limits, whose to say the acetaldehyde or nitric oxide level or 1 of the many other chemicals in the diesel fume is at an unsafe level, thereby not enabling "flush" mode on the "Rapid" units.
 
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Just another bit of information, in my area the Authority Having Jurisdiction would not allow a direct fired make-up air unit be installed without an interlocked exhaust fan.
 
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Goodwrench:

You may want to turn in a complaint to OSHA instead of approaching your employer. Employers have a way of not appreciating it when someone points out their shortcomings.

There is some good information available at:
 
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Another check would be to "beg or borrow" an air quality sensing unit such as used in rinks using propane powered zambonis. They are lunchbox sized and will record air quality (CO, CO2, NOx, SO, and many other undesirables) over a period of time. Usually used over a 24hr span with 1 minute intervals. This would give substance to your discussion with the employer or clear your mind. Better to confirm your concerns.

However, nobody should be subjected to poor air quality in a workplace.
 
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the carbon monoxide sensors may be defective, I would install a manual fresh air switch and a new sensor. good luck stay healthy.
 
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