Diesel Fumes, or more accurately Diesel Engine Exhaust Emissions (DEEEs) refers to the mixture of substances emitted from the exhaust of a diesel combustion engine.

DEEEs are composed of a cocktail of solid, liquid and gaseous substances, many of which are individually known to be hazardous to health, but which collectively were only classified as a group 1 carcinogen by the International Agency for Research on Cancer (IARC) in 2012 following a weeklong meeting of experts.

Within the workplace, categorizing or re-classifying a substance as a carcinogen increases the responsibility on the employer – whereas the ALARP (As Low as is Reasonably Practicable) principle applies generally under the chemical regulations, for carcinogens exposure must be kept “As low as is technically possible”, a statement that leaves very little wriggle room for the employer. The reason for the change in emphasis for carcinogens is there tends not to be a safe level of exposure (at least for non-threshold carcinogens), with the risk scaling with exposure but not dropping off or disappearing entirely at low levels as is the case for many toxic substances. This makes setting OELs a cold statistical exercise – instead of being able to state a safe levels, instead we have to determine an “acceptable” level of mortality.

The primary hazardous components of DEEEs include Nitrogen oxides, Carbon monoxide, Carbon dioxide, Fine particulate matter, Sulphur dioxide, PAHs and various hydrocarbons, though there are many more in smaller amounts such as arsenic, benzene formaldehyde etc. DEEEs are known to affect human health directly through their acute effects (nausea, eye irritation, lung inflammation, worsening of existing lung conditions), and also exert chronic effects such as reducing lung function, lowering resistance to infection and increasing the risk of cancer.

The traditional way of assessing exposure to an airborne contaminant is to measure its concentration in air. Measuring a substance that contains a mixture of hundreds of different components that simultaneously exist in the solid, liquid and gaseous phases is obviously difficult if not impossible, and over the years the practice has been to either use simple rules of thumb (i.e visible smoke, soot deposits) or instead identify one substances as an indicator of exposure and quantify that. One such substance is Carbon dioxide, though this has the disadvantage of being created by all combustion and some other processes. Another that has gained more prominence recently is Elemental Carbon (EC). Elemental Carbon has the advantage of being more specific to diesel engine combustion than CO2, though until relatively recently was more difficult to measure. EC concentrations in air are measured using a pre-baked quartz filter, at a flow rate of 2 – 4 litres per minute.

The exposure limit value for exhaust emissions when measured as EC is 0.05 mg/m³, as set by the European Agency for Safety and Health at Work. This becomes effective in general occupational health environments on the 21^st of February 2023, with a derogation for mining and underground works until 2026.

As with any chemical hazard, the preferred approach is to follow the hierarchy of control; the switch to electric drivetrain vehicles is a common, but costly, way of eliminating the problem. For static sources, Local Exhaust Ventilation (LEV) can be very effective at controlling emissions. Good workplace design, effective general ventilation, good vehicle maintenance, installation of DPF (Diesel Particulate filters) and other measures can also help. Respiratory Protective Equipment, though it can be technically effective, is not normally an appropriate control measure, because exposure tends to be spread out over much or all of the day, and long-term use of RPE should generally be avoided in most workplace situations. In addition, because DEEEs contain a mixture of substances, simple particulate filters alone are not sufficient.