I have seen a few threads here such as: thread1043-264841: Diesel and Gasoline Exhaust
that tried to touch on ventilation for vehicles in enclosed or semi-enclosed occupied areas. Most peoples' responses in the few threads out there dealt with a direct connection to the vehicle exhaust pipe and using a natural draft or forced draft system to blow the exhaust out of the building. The ACGIH Industrial Ventilation manual covers these decently. Unfortunately that doesn't always work in a lot of industrial forklift type settings.
I am working on designing the HVAC systems for an industrial manufacturing facility that will be using diesel-powered forklifts to transport coils of metal inside a warehouse and to the loading dock. Unfortunately in this kind of setting, the "connect directly to the exhaust pipe" setup just doesn't work with the way the trucks need to move around freely. ACGIH Industrial Ventilation discusses this very briefly and gives a few empirical values of dilution exhaust rates per type of vehicle with some constraints.
For example: 100 CFM per HP of each diesel vehicle operating assuming the vehicle operates 4 hours or less per shift and the volume of the space provides at least 150,000 ft3 per vehicle.
The problem here is that this situation isn't exactly addressed in the building code. They do address fully enclosed parking garages and recommend between 0.75 and 1.5 CFM/ft2 depending on which code year you use. However, they also assume limited occupation time by the people in there, not 8+ hour shifts like workers in manufacturing facilities.
My approach so far has been to compare several different methods/calculations relating to diluting vehicular exhaust:
1) The IMC 2003, 2006, and 2009 prescriptive methods for parking garage exhaust - not exactly the case but it is tangentially related and in the code which is law so it is worth looking at.
2) ASHRAE 62.1 ventilation for parking garages (same rates as IMC)
3) ASHRAE Fundamentals 2009 - Chapter 13 - Enclosed Vehicular Facilities. They provide a formula to calculate exhaust rates to maintain CO contaminants for 15, 25, and 35 ppm TWA limits. This requires knowing/estimating how many vehicles are in operation, how much CO in lb/hr they produce, and how long the vehicles are in constant operation. I gathered the best preliminary information I could here.
4) ACGIH Industrial Ventilation. 100 CFM per HP of each diesel vehicle operating assuming the vehicle operates 4 hours or less per shift and the volume of the space provides at least 150,000 ft3 per vehicle. I meet the volume assumption but these things will be operating nearly around the clock. For now I have scaled this information linearly using the basis of 8 hours of operation. Thus, I am using 200 CFM per HP of each of the vehicles instead of the 100 CFM for 4 hours of operation.
I am comparing all 4 of these methods and using the most conservative CFM as my basis for now.
Does anyone else have any input or any real-world experience dealing with this kind of scenario? I would love to get some feedback!