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Ventilation of Diesel-Powered Forklifts/Trucks in Enclosed Warehouses

Ventilation of Diesel-Powered Forklifts/Trucks in Enclosed Warehouses

Ventilation of Diesel-Powered Forklifts/Trucks in Enclosed Warehouses

Hi all,

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!

RE: Ventilation of Diesel-Powered Forklifts/Trucks in Enclosed Warehouses

Many years ago I toured a salt mine, a thousand feet under Lake St.Clair.  

The loosened salt rock was carried from the working face to an elevator by Diesel-powered, electric-steered, articulated bucket loaders, each driven by Mario Andretti or a reasonable facsimile.  I think they had rudimentary exhaust particulate filters.  I saw no evidence they had governors.

The entire mined volume was divided by bulkheads into two air channels, going from/to the ventilation shaft.  No matter where you stood in that enormous cavity, the air around you was moving enough to whistle slightly, and your throat got dry within just a few minutes.


Mike Halloran
Pembroke Pines, FL, USA

RE: Ventilation of Diesel-Powered Forklifts/Trucks in Enclosed Warehouses

"...your throat got dry within just a few minutes..."but at least you did not get headaches and poisoning from carbon monoxide.

MECHJAMIECTA, you should base your CFM on that TLV for CO and diesel fume particulates published by ACGIH instead of their rule of thumb of 100 cfm/hp.  This means  that you must figure out the generation rates of the contaminants, the volume of the work space but not necessarily of the entire volume of the structure housing the work environment, and the acceptable levels of the contaminants for an 8 hr exposure unless overtime is expected which then has to be modified. I am assuming that you have three shifts.  Your hardest objective will be to determined the generation rates of the contaminants.   

RE: Ventilation of Diesel-Powered Forklifts/Trucks in Enclosed Warehouses

Here is a general equation that you can use once you know the generation rate (=G) of the lowest TLV(=C) values, the ventilation air flow (=Q) and Volume (=V)of the work environment, time to ventilate; time (=T) required to reach the acceptable level of contaminants. Note: Q and G are assumed constant to simplify the integration of the following equation:
Integration will yield a general exponential solution:
From this exponential solution you can develop three cases:
Case 1)  C1=0 and G>0 in order to determine C2 when you kown G,Q,V
Case 2)  T>>T1 and G>0 in order to find Q=G/C2 where C2 is the   acceptable contaminant level which is the equation you need.
Case 3)  G=0 for intermittent sources.

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