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.