SYMPOSIUM SERIES NO 162 HAZARDS 27 © 2017 IChemE

1

Practical application of the Chemical and Downstream Oil Industry Forum

(CDOIF) Guideline “Environmental Risk Tolerability for COMAH

Establishments”

Ron Graham BSc CEng FIMechE, COMAH Manager, Sellafield Ltd, Seascale, Cumbria CA20 1PG

Introduction

Sellafield Ltd is registered as a Lower Tier establishment under the Control of Major Accident Hazards (COMAH)

(CDOIF) guideline “Environmental Risk Tolerability for COMAH Establishments 2013 [1], and the “Guidance on the

Interpretation of Major Accident to the Environment for the Purpose of the COMAH Regulations”, by the Department of the

Environment, Transport and the Region (DETR) [2].

The assessment method employed was tailored to facilitate application of the CDOIF method for assessing the risk of Major

Accident to the Environment (MATTE), and incorporates the CDOIF risk ranking method and matrix.

Definition of a Major Accident to the Environment (MATTE)

COMAH 2015 clarifies the definition of a MATTE by the following text: ‘an incident will also be a major accident if it

results in serious danger, whether realised or potential, to the natural or built environment. The effect may be immediate or

delayed and may sometimes be relatively long-lasting but not necessarily irreversible. Operators should consider the

potential for widespread loss or damage to the general environment as well as the risk adverse effects on a rare, unique or

outlined within CDOIF and DETR Guidelines

 Source – Assessment of the properties of the substance, identification of environmental hazards and potential

impact on receptors

 Pathway – Review of onsite pathways, assessing how a release could breach site containment and the

assessment of offsite pathways to identified vulnerable receptors

 Receptor – Determination of the consequences of release on vulnerable receptors, with analysis of the

environmental tolerability by the receptor. This is further assessed considering:

o Severity of harm on the receptor (the extent of the effect in terms of area % or of habitat affected)

o The harm duration and / or receptor recovery timeframe

In addition to the severity and harm of the scenario, the likelihood of the scenario occurring is used to find the overall

required to provide a refined understanding of the level of risk posed and the effectiveness of the safeguarding measures in

place.

MATTE threshold criteria are outlined below within Table 1.

SYMPOSIUM SERIES NO 162 HAZARDS 27 © 2017 IChemE

2

Table 1: MATTE Definitions and Damage Criteria

If the unmitigated risk is considered to be ‘intolerable’ or tolerable if as far as reasonably practicable (TifALARP), then risk

management strategies would normally be considered within a MATTE assessment. (Hierarchy of control)

guidance. The severity levels of Significant, Severe, Major and Catastrophic are also established within the guidance for

each receptor type, with guidance included on the boundaries between these severities of harm categories. The severity of

harm levels for each receptor type is duplicated from the CDOIF guidance in Table 1.1.

Table 1.1: MATTE Severity of Harm

Duration of Harm

In addition to the severity of harm for a scenario, the duration of harm (i.e. exposure and the time for recovery) must be

reviewed to allow the complete extent of an unmitigated potential for MATTE to be assessed. In the CDOIF methodology

for an incident to be considered as a major accident, there must be persistence in the effects caused, or alternately a delay in

recovery of the environment to pre-incident conditions. The criteria for duration of harm varies depending on receptor

SYMPOSIUM SERIES NO 162 HAZARDS 27 © 2017 IChemE

3

Table 1.2: MATTE Duration of Harm

MATTE tolerability can be determined by application of the CDOIF tolerability matrix, as shown in Table 1.3.

A CDOIF risk matrix can be used, from the values in the table which allows easy visualisation of the frequencies and

tolerability regions with regards to varying degrees of MATTE scenarios, as contained in the CDOIF Tolerability matrix

Table 1.4. This represents aggregated risk by receptor (i.e. it combines risk from all contributors in its evaluation of

tolerability).

SYMPOSIUM SERIES NO 162 HAZARDS 27 © 2017 IChemE

4

Table 1.4: CDOIF Tolerability Matrix

 Red – Intolerable Risk

If a scenario produces an outcome within the TifALARP (orange) or Intolerable (red) categories then a risk management

strategy should be assessed for elimination/ mitigation. Additionally a scenario outcome of Broadly Acceptable (green) does

not by itself infer ALARP has been demonstrated. The tolerability matrix is used to benchmark both mitigated and

unmitigated risk.

Phase 1of the Project

Initial data review and identification of priority facilities

The Establishment major Chemical Hazard Inventory (EMCHI) provided

 Substances

 Location

hazardous substances, the highest risk catchment areas and the highest risk local environmental receptors and if substances

on site could affect them.

 Review of potential MATTE (with completion of CDOIF tables)

 MATTE substances Table 1 (CDOIF App 5)

 Receptors in the local environment under the CDOIF definitions for MATTE if affected by events

greater than their thresholds (Table 2 CDOIF App 5)

 Definition of scenarios / substances which could affect receptors at / above the levels for potential

MATTE including all credible and high consequence events (Table 3 CDOIF App 5)

 Substance hazard information for confirmed MATTE risk substances (Table 4 CDOIF App 5)

 The CDOIF guidelines require the risk level of an unmitigated release to be determined and compared to a set of

It is important that the initial screening process is completed with the relevant expertise to ensure confidence in a detailed

assessment programme. This avoids organisations trying to carry out detailed assessments on relatively minor scenarios

creating unnecessary and expensive work.

Phase 1 Outcome

 Assessment of substances held on site and their locations

 Identified highest risk facilities

SYMPOSIUM SERIES NO 162 HAZARDS 27 © 2017 IChemE

5

 Highest quantity of substances

 Most hazardous substances

 Identified highest risk ‘catchment areas’

 Identified highest risk environmental receptors

 Initiated the creation of a prioritised programme for detailed Environmental Risk Assessment (Phase 2)

Phase 2 of the Project Overview

 Assessment and review of unmitigated ‘worst case’ scenarios

 Assessment and review of ‘mitigated’ scenarios

 Risk evaluation and ALARP assessment

Pre-Study and Information Gathering / Desktop Review

Extensive research and information gathering was carried out prior to the onsite study to allow the assessments to be

conducted effectively.

Key information gathered:

 COMAH dangerous substance inventory

 Manufacturer’s safety data sheets (MSDS)

 Control of Substances Hazardous to Health (COSHH) assessments

 Other designated land (LNR, AONB, ESA, NSA, greenbelt, national parks, wildlife trusts, national trust, common

land / country parks

SYMPOSIUM SERIES NO 162 HAZARDS 27 © 2017 IChemE

6

SYMPOSIUM SERIES NO 162 HAZARDS 27 © 2017 IChemE

7

SYMPOSIUM SERIES NO 162 HAZARDS 27 © 2017 IChemE

8

SYMPOSIUM SERIES NO 162 HAZARDS 27 © 2017 IChemE

9