Criterion 3.3 "The safety report should identify all potential major accidents and define a representative and sufficient set for the purpose of risk assessment."
This criterion reminds Assessors that they need to check that:-
Ideally, the Operator should summarise, in a proportionate way, the results of hazard studies, the methods used and the expertise of the team involved. The scope of the studies and the HAZID process used should also be described. To provide a convincing demonstration that the list of MAs is complete, the process needs to be systematic, ie each plant and its operational sequences should be considered in turn, including the possibility of interactions. Assessors should judge the completeness and adequacy of the way these issues are dealt with by asking the following questions:-
Operators are likely to refer to a list of fire initiators because these are common to all warehouse sites. In the case of explosions, fire is probably the main initiator, but the report should demonstrate that no other accident initiators have been overlooked. Assessors should take into account the scale of the hazards when making a decision on this issue (proportionality).
The accident analysis should identify all potential off-site initiators of major accidents and an indication of their likelihood (see Table 1). Other environmental initiators such as a freak storm and subsidence do not necessarily cause a fire. Assessors should not expect to see a detailed derivation of fire probability for on and off-site initiators; in most cases, the Operators will assign frequencies on the basis of engineering judgement or historical records
Many chemical warehouse sites store LPG for fork lift trucks and diesel for HGVs outside the warehouse. Others have small segregated stores containing peroxides or highly toxic or highly flammable substances. The accident identification process should not be restricted to the main warehouse, but should describe the consequences of accidents involving these additional hazardous substances.
The safety report should describe the consequences of an explosion if the warehouse contains explosive substances and a large spill if it stores toxic or eco-toxic liquids in bulk. Fires present three hazards, - thermal radiation from the flame pillar, a smoke plume that contains substances hazardous to health, and run-off of contaminated water. All of these should be addressed in detail. The hazards from LPG and diesel storage should be addressed if they extend off-site, but the detail should be proportional to the off-site risk.
At some sites a fire in one warehouse can spread to another. A safety report does not need to determine the consequences of two warehouses on fire simultaneously, but it should independently consider fires in different warehouses if these contain different substances, or, by virtue of their location or construction, present a different off site risk to local populations or the environment.
Fire in chemical warehouses can give rise to:-
All of these should be addressed in the safety report. Some are more probable than others, but those contributing little to the total risk should not be ignored. Operators of warehouses that do not store explosive substances should not ignore explosions completely, but state that explosions are very unlikely because of the absence of explosive material.
Criterion 3.3.1 "The safety report should demonstrate that a systematic process has been used to identify all foreseeable major accidents."
A systematic accident identification process is more important for chemical processing plant than for warehouse sites, but to judge compliance with this criterion Assessors can ask the following questions:-
Systematic approaches such as HAZOP,event tree analysis and failure modes and effects analysis are probably not appropriate for warehouse sites, but all accident (fire) initiators should be discussed. Since the majority of these are common to all sites, it is permissible for Operators to simply list them and deal with each one in turn. Compliance with the regulation is then a matter of checking if the Operators list is complete when compared to that given in Table 1.
Explosions can damage houses, listed buildings, nearby office blocks and chemical plant. Assessors should expect to see all of these potential consequences addressed. Safety reports that neglect of any one of them should be considered deficient, unless it is obvious that the hazard cannot be realised (e.g. explosive material not stored).
Criterion 3.3.2 "The hazard identification methods used should be appropriate for the scale and nature of the hazards."
Hazard studies employing HAZID techniques are widely used in the chemical industry and can be carried out at various stages during the lifecycle of a plant. They are systematic way of managing hazard over time, from the business requirement stage through to demolition and disposal. HAZID techniques seek to identify hazards in an absolute or relative way. Relative methods use checklists or hazard indices based on experience and lessons from incidents. Absolute methods are based on deviations from design intent eg HAZOP. Details can be found in Lees (1996), Kletz (1999) and CCPS (1989).
Methods (listed in increasing proportionality) that might be used include:-
Whatever approach is used, it must be documented as part of the safety report, or separately - in which case the main findings should be summarised in the report. As proportionality increases, and particularly in the case of new novel plant, some use of absolute methods is normally required. Both type of method need to consider 'common cause/mode' failures such as loss of power, or other services.
In order to test compliance with this criterion the Assessor can ask the following questions:-
The safety report should describe and justify the method used to identify major accident hazards. Assessors who are not convinced that all accident scenarios have been identified may deem the report 'non compliant'. However, use of a formalised accident identification process is not essential and an approach that is not completely systematic, but is seen as 'fit for purpose' is acceptable.
When explosions are not major accident hazards, the safety report only needs to consider the consequences of spills and fires initiated by off-site or on-site events. These are listed in Table 1 and each one should be addressed. A safety report that fails to discuss systems and procedures to minimise the risk from accidents may fail to meet the assessment criteria. Discussions of off-site accident initiators for warehouses in isolated locations, where very few if any people are at risk, do not need to be very detailed.
Safety reports for warehouse sites that store explosive materials must consider all the different ways an explosion can be triggered and describe the safeguards that are in place to prevent such events occurring. The consequences that should be addressed are blast over pressure, missiles and knock-on effects. Organic peroxides can give rise to an explosion, an intense fire and a fireball. The consequences of all of these should be determined in the safety report.
The principal initiators of explosions are fire, spills that result in fire, or any other event that produces localised and prolonged high temperatures such as an overloaded electrical cable, a steam pipe, an exothermic chemical reaction or an overheated fork-lift truck. The safety report should address each of these in turn and show that the risk is controlled and tolerable.
The safety report should consider ways, in which the contents of large drums and IBCs containing toxic or eco-toxic liquids can be spilt. In particular, leaks, punctures and sabotage should be addressed and the safety report should demonstrate that all necessary measures have been implemented to reduce the risk of spilt material leaving the site.