Controlling diesel engine exhaust emissions in enclosed spaces such as maintenance workshops is easily done with local exhaust ventilation (LEV), which can be as simple as fitting pipes to the vehicles’ exhausts while they are being serviced in order to draw the fumes outside. However, there are situations where this is not an option, for example in a warehouse where there is heavy vehicle movement inside the building, as vans and lorries come in and out for loading and unloading.
Controlling diesel exhaust emissions is not a one-size-fits-all solution type of problem
The HSE provides information on the health risks of diesel fumes in INDG286 and detailed guidance on how to control exposure to exhaust emissions in the workplace in HSG187. This is, however, very prescriptive guidance, and can be difficult or expensive to apply in situations such as the one faced by the Royal Mail’s Parcelforce in their sorting and distribution centres. These are converted warehouses that can contain up to 150 vans at any one time – all of them entering and exiting the building at similar times.The standard prescriptive solutions focus on the air change rate, which in the case of Parcelforce’s sorting centres would have meant 6 - 10 air changes per hour. This doesn’t take into account the variations in the levels of diesel exhaust in the air at different times. There would be peaks at the times vans drive in or out, but levels would go down whey they were stationary while loading or unloading the parcels, or when the building was empty between rounds of deliveries and collections.
Considerations when designing an effective ventilation system
When faced with a situation where LEV is not possible, finding an effective and cost efficient solution may require a little thinking outside the box. The first step is to analyse the layout of the building, its use, vehicle movements, and the size and type of the vehicles’ engines (which will tell you their emissions levels).
This type of facility is usually unheated. This is an important consideration, as exhaust fumes are relatively hot, so will tend to rise, but in an unheated space they will cool as they rise and may not reach the roof extracts, requiring low and high level extract grilles.
Monitoring the air quality and linking CO detection to the ventilation system can add a further level of efficiency, matching the extraction rates to the actual levels of emissions in the air at any time.
An effective and cost efficient approach
Going back to our example of Parcelforce’s sorting and distribution centres, the solution we developed achieves cross flow via natural inlet air and mechanical extract with a combination of axial fans and natural ventilators. These are triggered by CO detectors when emissions levels reached a predetermined level. This means that mechanical extraction fans operate only when needed, significantly cutting operating costs.
In our approach, we thought outside the box and developed a system that doesn’t fit within the prescriptive solutions in Approved document F. However, its implementation was possible because of our early involvement, which enabled us to support the M&E consultant from initial design through to approval with building control. So, if you are in a situation where LEV won’t do and need help with designing a bespoke solution, it is a good idea to involve the experts from the very early stages of your project.
For more information, view our Parcelforce case history.
Paul Langford is an Engineering Director experienced in product development, manufacturing & testing for HVAC, solar shading, louvre systems and smoke control.