Ventilation Requirements for a 9ft deep pit used for toe set operation

[musa86]

Hello Guys,

I am doing some ventilation and exhaust calculations for an underground pit which is used for the toe in operation in automotive industry. I was wondering what is the minimum exhaust or ventilation criteria for this application. I have come across 6 ACH but I am not sure and I don't have any references. Please advise and if you could tell me the code/reference to ASHRAE or ACGIH or anything, that will be great. Thanks

 

[EnergyProfessional]

need more information on occupancy, type of contaminants etc. Often you need to find some industry-specific standards or look at OSHA guidelines.

your specific case likely isn't covered by ASHRAE or code.

 

[jmaglott]

I recently found that the electrical classification of a pit depends on the ventilation. I reviewed NEC 2012 (NFPA 70) Article 511 and found it more helpful than ASHRAE or IMC for pit ventilation.

 

[Compositepro]

Pits are often classified as confined spaces with entry permit requirements by OSHA and therefore have been historically been replaced by vehicle lifts. Gasoline fume like to accumulate in pits.

 

[berkshire]

As an apprentice,
I did a few of these, the uaual treatment was a metalic duct 4" in diameter clamped into the corner of the pit terminating one diameter above the floor of the pit, with ducting in a channel across the floor of the building to a point outside the building. Then a centrifugal fan with a TEFC motor, and a duct away from anything flammable, usually up the side of the building. This was good for CO and Gasoline fumes.
B.E.

 

[chicopee]

9' deep pits to work under cars, that does not make sense. Most pits that I have seen were may be 4-1/2' or slightly more.

 

[berkshire]

chicopee.
You are right, Most of the pits I worked on were 4.5 to 5.0 deep. The 9 feet deep ones were for Tricloroethane tanks for degreasers.
B.E.

 

[chicopee]

I suspect that trichlorethane or trichloroethylene tanks have refrigeration coils incorporated into the tank walls to condense the vapors, so based on the likelyhood there is a refrigeration malfunction, I would want an air flow rate of 50 ft/min thru a cross section of approximately an average person's height starting at pit floor level times pit width.

 

[berkshire]

chicopee,
You are right, Most of the tanks used to have chilled water coils about 2 feet down from the top of the tank. The vent fan at the base of the pit was to catch fugitive vapors that cascaded over as parts were moved in and out of the tanks.
During operation of those degreasing baths , nobody was allowed into the pit. Maintenance personel were only allowed down there after the heaters had been shut off for several hours. Then only with a lifeline attached and a watch person on the top of the pit.And the vent fan running!
For the most part these things are going away because of Environment agency and EPA rules.
B.E.

 

[chicopee]

Well, thanks Berkshire, I have now learned the purpose of a 9' deep pit. I appreciate the information.