Proportionality is a concept that should be applied to determine the allocation of resource and effort to a safety and environmental argument based on its risk.  It is a difficult concept to attempt to distil into a process as each Product, System or Service will have different risks, objectives, priorities and interfaces that make a ‘one size fits all’ approach impossible.

A fundamental consideration of a proportional approach is considering compliance against assessment criteria.  The Health and Safety Executive’s view is that there should be some proportionality between the magnitude of the risk and the measures taken to control the risk. The phrase “all measures necessary” should be interpreted with this principle in mind. Both the likelihood of accidents occurring and the severity of the worst possible accident determine proportionality.  Application of proportionality should highlight the hazardous activities for which the Duty Holder should provide the most detailed arguments to support the ALARP demonstration.

Some important points that should be noted regarding safety and environmental proportionality approach are that:

1. Proportionality is inherent to safety and environmental risk assessment (i.e. use of ALARP, BPEO, etc.);
2. Proportionality is explicitly linked to risk;
3. Multiple factors need to be considered when deciding a proportional approach;
4. ASEMS is the mandated safety and environmental framework; therefore, the framework should be applied; it is not possible to develop a proportional approach that negates any part of ASEMS.

The model that should be used to consider a proportional approach is intended to provide guidance and should only be used by competent safety and environmental practitioners.  A degree of judgement should be used when answering questions, particularly where a Product, System or Service may easily be classified in more than one category; this is why the use of competent safety and environmental practioners is required.

During the process two initial questions are asked, where an answer of “yes” will automatically result in a categorisation of high risk, regardless of the answer to subsequent questions.  Further refinement is required for lower risk systems to ensure that the system risk is categorised appropriately

The diagram above depicts the proportionality waterfall approach model used for the application of ASEMS.

Once the risk category has been established guidance is defined which prescribes the rigour which should be applied to the safety assessment process in terms of Process, Effort, Competence, Output, Assurance (PECOA):

1. Process - the amount of dedicated/specific process, level of intervention in the organisational structure the Safety and Environmental Management System are established;
2. Effort - How much time is afforded to the management of risk;
3. Competence - the level of competence that is required to conducted appropriate assessment and management of safety and environmental;
4. Output - The detail of evidence and reporting is cognisant to the level of risk;
5. Assurance - The level of assurance required which shall be applied to the process.

It is a fundamental requirement of ASEMS safety management principles that all safety decisions made should be reviewed, assessed and endorsed by a Safety and Environmental Management Committee to ensure that the Products, Systems and Services categorisation is correct. The diagram below shows the process that may be applied:

It should be remembered that using this low/medium and high categorisation could be misleading as the model takes no account of the population or rate of occurrence of the harm. A simple system that can only cause minor injury could still have a high degree of risk if there are lots of people exposed to the risk and the accident rate was high.  Moreover, acceptance of such a situation could lead to the development of an ineffective safety culture or the bypassing of safety mitigation procedures in order to avoid a high accident/minor injury position.  This is where the application of competent safety and environmental advice is essential to ensure that any proportionality model is not slavishly followed at the expense of proper rigour.   Where this model is useful is assisting those safety and environmental professionals to perform a preliminary assessment regarding what Products, Systems or Services are a priority for the allocation of resource, time or effort.

The first question is used to indicate, at a high level, the likely degree of risk for a project.  It should be noted that this is not a definitive assessment and that Products, Systems or Services could move within the model as the safety or environmental evidence is assessed.  There will be a degree of pre-existing assessment which accompanies a Product, System or Service and this may be used to assist with this initial question. 

The safety and environmental assessment process should be closely aligned with the Product, System or Service development process for newly developed Product, System or Services.  Where Products, Systems or Services are in the Concept, Assessment, Development or Manufacture phase of the CADMID/T cycle, they should be accompanied by a safety and environmental assessment process which utilises quantitative assessment techniques.

Where a Product, System or Service sits in the CADMID/T cycle should not influence the rigour of any safety or environmental argument; this model is provided to assist with any determination of the resource, time or effort that may be applied to the evidence to support the argument.  All Risk to Life should be ALARP, with no exception; what changes is the allocation of resources, time and effort to reach that judgement.

Commercial Off The Shelf or Military Off The Shelf systems should be accompanied by evidence which may be used in the safety and environmental assessment to demonstrate that they are acceptably safe and environmentally compliant, particularly where these are manufactured for use in the EU, where each Product, System or Service should demonstrate compliance with the applicable EU standards.  That the Product, System or Service is Commercial Off The Shelf or Military Off The Shelf is not, in itself, evidence.

Such evidence should include test evidence, trials evidence or a certificate of conformance.  Where a Commercial Off The Shelf or Military Off the Shelf system is already in the in-service phase and it is established that there is sufficient evidence to form a compelling safety argument that the Risk to Life is ALARP, then the system should be categorised as MEDIUM-LOW.  Where the system is also non-complex then it may be categorised as LOW.

If the worst credible consequence is a single fatality or multiple severe injuries then the system complexity should be considered further to refine and inform the categorisation.  Complex or novel system designs should have a higher degree of Suitably Qualified Experienced Personnel to conduct the safety and environmental assessment.  Accordingly, those Products Systems or Services which are complex and novel should also be categorised as HIGH whereas those exhibiting a lower degree of complexity might be categorised as MEDIUM.

LOW risk Products, Systems or Services were the worst credible consequence is at worst a single minor injury should be categorised as LOW-MEDIUM risk where the design is complex or novel, those exhibiting a lower degree of complexity should be categorised as LOW risk.

A qualitative safety and environmental assessment process should be applied to Products, Systems or Services, which are in the In-Service, Disposal/Termination phase where it is deemed that there is sufficient evidence already in existence to demonstrate that it is acceptably safe.  In these circumstances a qualitative safety and environmental process should be applied to assess the in-service risks.

If a Product System or Service is assessed to be in a particularly low category and is simple it may not be necessary to undertake the full scope of risk management procedures.  In these circumstances a certificate of conformance may be sufficient, which may be supported by statement to that effect from the Safety and Environmental Management Committee.

The safety and environmental lead for MEDIUM category projects should be at least practitioner level.  The remaining personnel engaged on such projects should be practitioner or supervised practitioner where appropriate supervision is in place.  A competency assessment should be undertaken which should be endorsed by a Safety and Environmental Management Committee.

Competency requirements relating to specific safety and environmental processes defined in ASEMS should be applied where those processes are undertaken.

A safety and environmental case should be developed for HIGH category projects which includes a safety and environmental argument, developed using Claims Arguments Evidence (CAE) or Goal Structuring Notation (GSN).  The argument should be substantiated by quantitative evidence such as reliability data or the output from quantitative safety assessment processes.

A Safety and environmental case should be developed for MEDIUM-LOW category Products, Systems or Services.  A safety and environmental argument should be included for those Products, Systems or Services which are particularly complex or novel or those which exhibit an increased degree of risk

A safety and environmental case or Safety and environmental statement should be developed for LOW category Products, Systems or Services.  A certificate of conformance may be adequate for the lowest risk simple Products, Systems or Services

MEDIUM-LOW category projects should be independently reviewed by a Safety and Environmental Auditor where the safety and assessment processes applied are novel or complex.  Justification should be provided where an Independent Safety and Environmental Auditor is not appointed.

It is not necessary for projects categorised LOW to be independently reviewed.