The identification of major accidents needs to be systematic and must cover normal and abnormal operations.
One of the purposes of a COMAH Safety Report is 'demonstrating that the major accident hazards and possible major accident scenarios in relation to the establishment have been identified and that the necessary measures have been taken to prevent such accidents and to limit their consequences for human health and the environment'. A key part of this demonstration is the identification of potential Major Accident Hazards (MAH).
There is no right or wrong way to identify MAH under COMAH, and it is not a requirement of the COMAH Regulations 2015 that a quantified risk assessment is undertaken. Sometimes it is sufficient to provide a qualitative 'description of the possible major accident scenarios and their probability or the conditions under which they might occur', but usually an approach somewhere between the two is the most appropriate, i.e. a semi-quantified approach, depending on the risk profile of the site.
We have developed our own Process Hazard Analysis (PHA) techniques for identifying and assessing hazards, based on many years of experience with COMAH sites and feedback from the CA. We tailor our approach based on the severity of the potential hazards, and always try to utilise any existing risk assessments.
Extent and severity: who might get hurt and how badly?
Once you have identified your potential Major Accident Hazards (MAH), you then need to provide information on the extent and severity, i.e. who might get hurt and how badly, considering both harm to people and damage to the environment.
C3 personnel have experience in determining the consequences of MAH, using techniques ranging from qualitative descriptions, to detailed dispersion modelling of the events using computerised tools such as PHAST.
Consequence assessment is an important early stage in the preparation of the COMAH Safety Report as it helps you to determine the depth of demonstration needed, i.e. where consequences are minor a limited demonstration to show operations are carried out to current and relevant good practice may be adequate, but where consequences are more severe the demonstration needs to be stronger and will require a demonstration that the risk are As Low As Reasonably Practicable (ALARP).
ALARP demonstration is not an add-on to a risk assessment; it should be a fundamental part of it.
A COMAH Safety Report for an Upper Tier site needs to contain a demonstration that the risks are As Low As Reasonably Practicable (ALARP), which can be a straightforward exercise if your risks are low, but has the potential to be complicated for high hazard sites or those with few control measures. Some Lower Tier sites have also been required to prepare an ALARP demonstration, and again the complexity can vary depending on the site's risk profile.
Most risk matrices contain an area where the risks are 'Tolerable (if ALARP)'. The key word is the 'if', as events in this area are only tolerable if they are ALARP, which is why ALARP demonstration is such a key part of COMAH.
At C3 we have developed a simple (spreadsheet based) tool that guides you through the ALARP demonstration process, asking the questions 'What more could be done?' and 'Why have we not done it?' Where it is not possible to qualitatively accept or reject a potential risk reduction measure, a more quantitative assessment is used based on cost benefit analysis to assess whether the cost associated with the measure is grossly disproportionate.
At C3 we know that there are many ways to achieve the same goal, therefore we will tailor our approach to align with your own existing hazard assessments and risk matrices.
C3 can also help with the initial hazard identification and risk assessment; the identification and screening of potential additional measures; comparison against good practice; and/or prioritisation of any measures that are calculated to be reasonably practicable.
Being inside a building does not always protect you from the hazards outside.
The location and design of occupied buildings has been a recurring theme since the Flixborough incident in 1974, and there have been many incidents since then such as BP Texas in 2005 that have killed or injured people who were in buildings at the time of the incident.
All Upper Tier COMAH sites need an up to date Occupied Buildings Risk Assessment (OBRA) that includes the impact of fire, explosion and toxic release events (where relevant) on the site's occupied buildings. Many Lower Tier sites are now also being asked to complete an assessment, as part of their demonstration of safe operation.
All assessments must be completed against the guidance published by the CIA in 2010, which contains baseline data for sites without any specific data for their hazards, and also contains guidance on how the assessment should be applied to permanent and temporary buildings.
A simple hazard-based approach can often be adequate, without unnecessary and expensive detail; but if a more detailed assessment is needed, C3 believe in using existing risk assessments where possible to provide consistency and minimize additional work.
C3 personnel have completed numerous assessments for chemical processing and storage sites, of varying hazards, size and complexity. We can also provide advice on the siting and integrity of toxic refuges, potential modifications to control systems to reduce the vulnerability of control rooms, and civil engineering support for any building modifications that may be required.
