SELECTING AND SPECIFYING A BASIS OF SAFETY

Having identified the chemical hazards of a process, it is necessary to decide how to design and operate the process safely — that is, to select a basis of safety. (See also case histories Al 27-30, pages 172-175.) 

The ideal process is inherently safe — no disturbance whatsoever can cause an accident. Absolute inherent safety is rare in practice, but the principles of inherent safety can be used to reduce the number, complexity and cost of addon safety measures, particulariy if the potential hazards are identified and considered in the early stages of process development and plant design. For example  

In most situations it will be necessary to provide additional safety measures, and these can be of two kinds preventive or protective . Preventive measures involve designing processes so that they do not operate under conditions which might allow an uncontrolled reaction. The mechanical design of the plant, its control system and the way in which the process is operated can all include preventive measures. 

Protective measures mitigate the consequences of a runaway reaction. Protective measures are rarely used on their own some preventive measures are usually included to reduce the demand on the protective system. The options for protective measures are  

Rather than dealing with the consequences of a runaway reaction it is usually better to prevent the runaway in the first place, so the designer should generally prefer preventive to protective safety measures. Whatever safety measures are chosen, it is important that they make the plant safe under the full range of operating conditions and credible maloperations and remain effective after plant modifications. 

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The above proposal is based on the characteristic controlling parameters for a certain type of hazard with a significant safety margin. Selection of a maximum drying temperature on the basis of the onset exotherm temperature has been verified extensively by Gibson et al. [15] the temperatures specified do not place an unacceptable restriction on drying operations. They have continued to be efficient and economic. 

IS015189 Medical Laboratories—-Particular Requirements for Quality and Competence is a universal standard for quahty management in medical laboratories that specifies requirements in general terms applicable to all medical laboratory fields, The standard is intended to form the basis for accreditation of medical laboratories. In addition to general laboratory conditions in relation to quality control, the standard focuses on medical competence, interpretation of test results, selection of tests, reference intervals, ethical aspects, and safety. An annex concerns quality management of laboratory computer systems. 

Establishing a procurement policy, which includes a pre-procurement risk assessment, will ensure that correct selection of plant and equipment for use in hazardous areas (where a flammable or explosive atmosphere has the potential to cause a fire or explosion) will minimise the risk relating to such equipment. BS EN 50020 2002, Electrical apparatus for potentially explosive atmospheres - Intrinsic safety i , specifies the construction and testing of intrinsically safe apparatus, intended for use in potentially explosive atmospheres and for associated apparatus, which is intended for connection to intrinsically safe circuits which enter such atmospheres. This document may well form the basis from which an organisation establishes its procurement policy for such equipment. 

Competence Criteria for Safety Related Practitioners (lET 2007) (also known as the Blue Book). This contains competencies which are intended to cover the range of an organisation s safety-related activities and includes fifteen criteria specifically aimed at ISAs. The aim is that the competencies specified can be selected on a pick and mix basis to adapt to specific industry requirements and to match particular job requirements. However, whilst it was considered that the ISA competencies provided were a good starting point, ISAs are generally required to have a broader set of skills than just the fifteen provided. Therefore more guidance needed to be provided to help select both from the ISA competencies and the remaining competencies. 

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