Environmental Risk Assessment – Are Companies Missing Critical Blind Spots and Risking a Major Accident?

In the article below, SLR’s Euan Munro (Associate Engineer, Process Safety and Process Engineering) discusses the potential for companies to have blind spots in regards to the environmental impact of their operating sites. Using his own experience and expertise, Euan explains the process of an Environmental Risk Assessment, which is the best way for companies to avoid a Major Accident to the Environment.

For industrial sites covered by the Control of Major Accident Hazard Regulations (COMAH), there is a legal requirement to complete a detailed Environmental Risk Assessment. Companies carry out these assessments to find if a Major Accident to the Environment (MATTE) could occur – and if so, ensuring that the risk is suitably controlled.

But for non-COMAH sites that don’t do MATTE assessments, are they missing critical blind spots and risking a major accident?

I’ve been involved in and led several MATTE assessments. For the majority of these, the scenario that could cause a MATTE, surprisingly, did not involve the main hazardous substances that brought the site under the COMAH regulations. These tended to be substances like diesel, for site vehicles, or other fuels for small site boilers.

This experience has led me to think there are many companies around the UK operating sites with the potential for a major environmental accident, but they don’t have a clear understanding of what the consequences would be. This could potentially lead to a critical blind spot where plant management does not have the right controls in place for an environmental accident, or are focussed on potential accidents with a lower risk of environmental harm.

Carrying out an Environmental Risk Assessment is the practical way to ensure any blind spots in Environmental Risk are revealed. Once the outcomes of known scenarios are quantified, efforts to mitigate them can be managed effectively.

The dominant methodology for completing assessments for COMAH sites (i.e. the method the UK’s environmental regulators prefer) is from the Chemical and Downstream Oil Industries Forum (CDOIF). While that may sound like it may not be relevant for sectors outside Oil & Gas, our MATTE team at SLR have been successfully working to this method for a range of sites.

The first part of this process is to understand all of the possible scenarios with the potential to cause serious environmental harm – at this point, it is key to keep an open mind and look at all the substances stored or made on site. This list can be dauntingly long at first, but fortunately, this can be trimmed down for the next step, as each scenario can be assessed by its worst-case.

The assessment of each scenario is done using the Source-Pathway-Receptor model. This is where a harmful release is traced from its release point (e.g. a leak from a tank). We then trace the flow of the release (e.g. through site surface water drains to sewer, or through unmade ground on the site). Once we fully develop the pathway, the final receptors affected by the release can be found, such as groundwater bodies, marine environments or surface water bodies (which can also be pathways to other receptors).

Finding out what the effect will be on the receptors is where I draw on knowledge from the range of experts in SLR such as ecologist, hydrologist, hydrogeologists and archaeologists to quantify what the outcome would be. This assessment is across two dimensions; the area of the impact and the duration of harm.

With this information, the MATTE tolerability is found – although this varies depending on the type of the receptor. For example, affecting 1 hectare of a ‘Site of Special Scientific Interest’ would have a “Severe” level of harm, but only a “Significant” level of harm for widespread habitat. The duration of harm also has different significance depending on the type of receptor; for surface water bodies, recovery in one to ten years is considered Medium term, however for groundwater Medium term is only between three months and six years.

The MATTE tolerability range is demonstrated with a scale, where A is the lowest and D is the highest – as well as there being sub-MATTE levels of harm. Each of these categories gives operators different frequencies of occurrence that can be deemed acceptable, tolerable or intolerable. While this sounds complex, it is simple to show as a risk assessment matrix.


The asssessment process may sound arduous, but at the end of it, plant managers can have a quantified level of environmental risk that particular substances or processes on their sites pose to the environment. Estimated financial costs for levels of MATTE can also be applied. However, these are only order-of-magnitude values.

For lower-risk sites that aren’t covered by COMAH, the number of scenarios that could cause a MATTE would likely be much lower. Furthermore, a “lighter-touch” approach could be taken to streamline the assessment process. This would give operators a quick, cost-effective route to understanding their environmental risk and start taking targeted steps to mitigate it.

In summary, I believe that there is a range of businesses that have blind spots in terms of the environmental risk of their sites. However, there is a suitable and structured method for assessing this risk in the form of CDOIF guidance for MATTE assessments. Carrying out an environmental risk assessment following this structure allows plant managers to effectively target their resources to mitigate the scenarios that could cause the most harm.

For more information please contact:

Euan Munro, Associate Engineer, Process Safety and Process Engineering at eamunro@slrconsulting.com

Key Contacts:

Euan Munro