Diesel exhaust emissions – what to measure?

fork truck

We recently had a query from a client who’d had a visit from their local Factory Inspector. The client has a large warehouse where they operate diesel powered fork lift trucks. The Inspector asked about the client about their risk assessment of the emissions and then suggested that they arrange to measure the emissions.

Diesel exhaust emissions are a complex mixture of gases and particulate matter. Major components include :

  • carbon;
  • nitrogen;
  • water;
  • carbon monoxide;
  • aldehydes;
  • nitrogen dioxide;
  • sulphur dioxide;
  • polycyclic aromatic hydrocarbons (PAHs).

Quite a number of these contaminants are irritant gases, that can affect the eyes and respiratory system. There are also concerns about the potential risk of cancer from inhaling this complex mixture. Some studies have shown a small increase in lung cancer for people exposed to diesel exhaust emissions and the International Agency for Research into Cancer (IARC) have concluded that diesel engine exhaust is probably carcinogenic to humans. This may be due to the presence of PAHs in the emissions.  Another consideration is that, due to the way it is formed, the particlulate matter is nano-sized, and can be absorbed through the lungs and transported around the body. There are concerns that nano-particles may cause adverse effects on the heart and cardiovascular system

Although a number of the individual components have Workplace Exposure Limits (WELs), and can be measured fairly easily, simply quantifying each substance does not give an adequate evaluation of the risk, particularly as there could be additive or more complex interactions. In any case, some of the components presenting the greatest concerns (nano-particles, PAHs) do not have WELs.

So although some components can be measured, it’s not so easy to interpret the results.  In such cases it is best to remember the real objective of risk assessments – i.e. to determine what controls are required. The HSE have published some guidance in their publication Control of diesel engine exhaust emissions in the workplace (HSG187). It is usually obvious when there is a significant problem with the emissions from diesel engines. If visible black smoke is pouring out of the exhaust pipe something needs to be done! It’s not always so obvious, but the UK Health and Safety Executive (HSE) have developed some guidelines based on observations, subjective assessment of irritancy and measurement of carbon dioxide levels, which give an indication of whether control is adequate.

Table 1 – Guidelines for the assessment of the level of exposure to DEEEs – From HSG 187

image

Carbon dioxide can be measured easily using a simple colorimetric indicator tube. But note that in this instance it isn’t appropriate to compare the results with the WEL for the gas – it is being used as an “marker” of the overall emissions and standard of control.

It’s quite possible to measure the particulates, but the analysis is very expensive and there isn’t a WEL. Without a standard against which the results can be compared, measurement results don’t help us to decide on the degree of risk and whether improved controls are needed. In this case, particulate sampling is an expensive exercise which doesn’t help us to draw useful conclusions. Using a pragmatic approach of observations and simple measurements of marker compounds is the most cost effective way of assessing the risk and deciding on what controls are needed.

The following provide some further information on the assessment and control of diesel engine exhaust emissions:

Health and Safety Executive – indg286 Diesel Engine Exhaust Emissions

Health and Safety Executive Control of diesel engine exhaust emissions in the workplace (HSG187)

Rogers and Davies Diesel Particulates—Recent Progress on an Old Issue The Annals of Occupational Hygiene 2005 Volume49, Issue6 Pp. 453-456

Diesel Engine Exhaust – California Department of Health Services

Photo credit: Stock:xchng

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