2 - Hazard Identification and Risk Assessment
Identification of hazard sources
Operational Hazard Sources
External Hazard Sources
Other sources related to design, construction and safety management
Assessment of prevention, control and mitigation measures
3 - Information concerning the Major Accident Prevention
Description of equipment
Description of mobilizable resources
Summary of elements for the internal emergency plan
Annex A - Article 9 and Annexes II & III of the Directive 96/82/EC
Article 9 and Annexes II & III of the Directive 96/82/EC of Council Directive 96/82/EC, on the control of major-accident hazards involving dangerous substances
Annex B - Hazardous Reactions and References
When hazardous reactions1 are involved within the processes of an installation the safety report should contain sufficient information to demonstrate that the operator has identified the major accident hazards and assessed the risks associated with the process. This should include:
The following issues should be addressed if relevant, and referenced data should be available related to:
It is not unusual for accidents initiated by runaway reactions to be accompanied by severe and irreversible consequences e.g. fatalities, damage requiring plant demolition and abandonment. In addition, industrial experience has shown that runaways are as likely to occur in medium/small sized 'non-major' hazards sites, as in major hazards sites. Hence the selection of a suitable methodology for the relevant hazards to be identified can be assisted by the inputs provided by the analysis of past events.
Among the most frequent immediate and underlying causes identified in past accidents specific to runaway reactions are:
SR should outline the principles and procedures followed to identify the hazards involved in runaway reactions. Hazard identification and risk assessment are particularly important and is best carried out by a team of qualified people such as chemical engineers and chemists, using various methods. Screening methods shall be addressed related to:
A. Classification of reacting system
The reacting system classification can contribute the recognition of hazards already identified in similar systems. Several criteria may be used i.e. Arrhenius and Non - Arrhenius reactions, homogeneous and heterogeneous runaways, combinations of initiating events including reactant accumulation, loss of cooling, external heating, solvent evaporation etc.
B. Hazard testing
Hazard testing is important and should be performed using various screening methods for the evaluation of the characteristic parameters of runaway. Hazard identification methods may require data on:
An indicative list of possible thermochemical parameters to be evaluated and the methods to be used for this is given below:
Hazard Identification Methods:
Operators should make the best use of available hazard data and if not sufficient laboratory and desk top tests should be performed to estimate the extent of hazard. In scaling up from laboratory to real size, uncertainties and necessary extrapolations involved in the reaction parameters should be also considered.
C. Risk assessment - preventive and mitigation measures
Risk assessment is essential to evaluate the likelihood of runaway and the severity of its potential consequences. The extent of risk analysis and the intensity of the preventive and mitigation measures should be commensurate to the risk involved. Simple models of hazard identification may not be always sufficient. A list of typical failure modes may be helpful.
There exist several approaches to perform risk assessment. The choice of a particular technique may be process-specific. Although detailed assessment using for example CHETAH indices is advisable in several cases, it cannot be considered always necessary unless otherwise sustained by cost-effective analysis. Simple screening techniques on the other hand, can be sufficient only when combined together with the scale and frequency the usual batch operations are performed, and thus could constitute an adequate basis for discussion criteria to whether further assessment is needed.
Inherently safer design includes substitutions, intensification and attenuation. A viable process would require the implementation of prevention and control measures such as sensors, trips, alarms, control systems, and protective and mitigation measures such as reactor emergency reliefs, crash cooling, reaction inhibition, secondary containment, etc.
Design reactor relief regulations applying in all circumstances are not common. Not venting may be acceptable when risk has been reduced to an acceptable level. The necessity of some measures, e.g. explosion vents, may sometimes need to be balanced against cost or environmental and technical constrains.
Emergency plans should consider among others injury to key emergency personnel. Re-examination of the measures taken in established processes may be needed when hazards are not adequately identified. Audits can contribute to this by providing considerable inputs and are expected to be triggered by the legal requirement of updating the Safety Report of installations involving hazardous reactions.