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Chemistry International
Vol. 24, No. 1
January 2002
Reports from Conferences
Safety in Chemical Production
The IUPAC Committee on Chemistry and Industry (COCI) has run a number of successful workshops with the theme Safety in Chemical Production over many years. The first of these was in Basel, Switzerland in 1990 and subsequent ones have been held in Yokohama, Japan 1993 and San Francisco, USA 1997. The fourth and last of these workshops was held 30 July-4 August 2001 in Dakar, Senegal as part of the 8th International Chemical Conference in Africa, under the auspices of the African Association of Pure and Applied Chemistry (AAPAC). Almost all of the 150 participants at the conference attended the workshop, which was presented by Daniel Rademeyer from ISHECON, a group of safety, health and environmental consultants. As the COCI member from South Africa, I organized the workshop, which centred on aspects of responsible care, hazard identification, and risk assessment in chemical production.
In the first part of the session Daniel dealt with the safety, health, and environmental (SHE) risks presented by chemical processes, in which a series of systematic reviews are conducted, in parallel and integrated with the process development activities.
The first review is done at an early stage of the development as a broad overview of SHE issues. Consideration is given to the hazards of the chemical materials involved in the process, the interactions between these, means of handling, suitability of the materials of construction and their implications for site selection, plant layout, process control, employee protection, effluent treatment, waste disposal, legal requirements, and design codes or standards. From this review enough information will usually be available to carry out an environmental impact assessment (EIA).
Once the conceptual design has been completed and major processing steps have been selected, the second review is undertaken. The major hazards are identified (e.g., fire, explosion, toxic release, pollution, and violent releases of energy) and preventative and protective measures are incorporated into the basic design phase. From this review enough information will be available to carry out formal risk assessments to establish whether adequate resources have been allocated to meet SHE targets.
Finally, a third review in the form of the traditional Hazard and Operability study (Hazop) is performed once the basic design has been completed. This is a thorough examination of the operability of the process in terms of dealing with deviations in operating conditions; e.g., pressure, temperature, concentration, and failures etc.
The above three reviews can be applied to the set-up in the research laboratory, the pilot plant, and the full-scale plant. Once the construction is almost complete, and before commissioning and introducing hazardous materials, a practical review is carried out to check whether all the requirements of the first, second, and third reviews have been incorporated. This may take the form of an audit.
Often, once hazards have been identified in chemical processes, various protective devices or systems are installed, which involve high costs. This can make a process uneconomical and in some cases lead to the closure of the plant with accompanying loss in revenue and jobs. In order to decide the optimum amount of money that must be spent on safety, it is necessary to assess the risk. This aspect was covered in the second half of the session.
Risk is the combination of the likelihood of occurrence of the hazard and the severity of the consequences. A release of chlorine from storage may be very serious (people may be gassed, so the severity is high), but the tank may be so secure that a leak is almost impossible (therefore, the likelihood is very small) and hence the risk will be low.
Likelihood of an event may be determined by using the so-called Fault Tree technique, where the event is broken down into its root causes. One may for example not know the likelihood of a release via the relief valve on a chlorine vessel. However, this may be simply broken down into the root causes of overfilling and heating in the sun. One may know how often the operator over-fills the vessel, as well as the duration of sunshine, which with the aid of the fault tree will reveal how often the relief valve may be expected to blow.
Consequence may be determined by calculation of the effect of the hazard (i.e., whether a person will suffer injuries). A chlorine release will be carried away by the wind and dispersed to lower concentrations, so that some distance away a person may suffer respiratory effects. In the case of a fire at some distance a person may suffer a certain degree of burns, or with an explosion, some blast injuries. The effects are usually related to the amount of chemical material in containment or the rate of release.
Combining likelihood and severity gives an estimate of the risk e.g. injuries per year. This is then compared to a target. If the target is exceeded, the risk is unacceptable and more money needs to be spent to make the system safer; i.e., reduce the risk. On the other hand, if the risk is below the target, no further action needs to be taken to improve the system.
Assessing the risk allows money to be spent, which is in relation to the risk. Thus if the risk is high the cost will be high and visa versa. This will ensure that unnecessary money is not spent on a chemical plant where the risk is low.
Some lively discussion took place at the end of the presentation and generally the content of the workshop was well received and thought provoking.
We can all learn from the use of these techniques, either in the research and development environment or at a full-scale plant. COCI is in the process of organizing the next workshop to take place in China in 2002.
Dr. M. D. Booth is Director of Information Resources for the Chemical & Allied Industries' Association.
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