Maintenance tunnel ventilation

[Badbird2000]

So, i am wrapping up a project for an automotive injection moleding facility. There is a maintenance shaft that runs through the plant, with an open set of stairs on one end and a normally closed hatch at the other. It's about 120' long, 8' tall. The only piping in the tunnel is carrying plastic pellets to injection molding machines. I need to ventilate this shaft, but can't find any air change per hour rates or any other values to tell me at what rate. I am going to stick the fan on the closed end and run a short piece of duct through the shaft, maybe a 1/3 of the way down towards the open end where the stairs are.

Anyone delt with something like this before? i can't find anything in OSHA or ASHRA.

Thanks!

 

[Drazen]

have you looked under confined space chapters? osha has extensive requirements regarding to that.

the ventilation issue cannot be separated from other issues, especially lockout/tagout procedure. your system will certainly need timed pre-ventilation and post-ventilation. flammability and explosive potential need to be taken into account.

ducting would be needed if you have openings on the same side, to prevent recycling or shortcutting, but if you lock your entrance door open with fan on the closed side working, it is likely not needed. in general flammable materials call for exhaust fan.

plastic molding plant should have safety director. stick to him, if you do not want to create risk of your own imprisoning.

 

[miningman]

Take the cross sectional area of the shaft, apply 50 feet per minute as an average flow velocity. This will give you the cfm value you need

 

[chicopee]

What is the diameter or other dimensions of the tunnel and what is the reason to ventilate the tunnel?.

 

[urgross]

I believe the IMC has listed a ventilation rate for unoccupied mechanical space. That would cover normal conditions.
As suggested above, safety and smoke control would be considerations.

 

[MTES93]

I think Drazen is on target. I think OSHA 29 CFR may have info. If they don't give an exact rate, I like miningman's approach...

http://www.osha.gov/pls/oshaweb/owastand.display_standard_group?p_toc_level=1&p_part_number=1910

 

[chicopee]

One still has to determine if contaminants such as injection molding fumes are expected and if maintenance people are to enter this tunnel to do their job while exposure to fumes exist.

 

[KiwiMace]

My worksite is laced with tunnels:
Shallow service tunnels are naturally ventilated with intermittent risers. This is a useful approach as the risers also provide an access point for getting lengths of pipe in.
Deeper tunnels are mechanically ventilated, with point to point supply and extract. Ventilation levels of these deeper tunnels are under review as the air velocity may need to decrease to limit fire propagation... I am not directly involved but I am hearing target of ~1 m/s (3-4 ft/s).