ABSTRACT
The Purpose of a Safety Case Why Are You Constructing a Safety Case? Before any safety case is attempted, the rationale and purpose of it must be clearly understood. This is vitally important, because if the specific requirements for compiling a safety case and writing the safety case report are not clear, then the following safety case will also be not clear. At best, a poor safety case will be of little use to whatever it was intended to apply to. It will remain a permanent record of your engineering style and capability – and if the safety work is poorly defined and poorly implemented, few customers are likely to remain in contact with you. At worst, you (personally as well as corporately) may have accidents that could actually have been forecast and prevented. Depending on your industry, you may therefore come under scrutiny from your regulators and other legislative bodies. Criminal charges could follow a stressful investigation. In some cases around the world, businesses have been forced to close. Many of the international standards and legislation relating to safety cases have an implied purpose attached to them. For example, in order to obtain permission to operate a nuclear power plant in the UK, you must develop a safety case and produce a safety case report describing it [HMSO 1965]. If you want the Australian Ministry of Defence to purchase your latest whiz-bang weapon, you will need to provide a safety case [AGDoD 1998]. These are legislative and procedural specifications that state that you shall provide a safety case. If you don’t have one, then you will not be able to operate in that market sector. Of course most of us don’t operate nuclear power plants, or sell to the Australian Government. But there are still reasons for developing safety cases. The Safety Case as a Record of Residual Risk For the consequences of some event, action or process to be defined as unsafe, there is some residual risk. If there were no risks at all, then there would be no reason for being concerned about safety – and you could close this book now and put it back on the shelf. The more likely case is that there is some level of risk in the course of action that is being considered. Developing a safety case through analysis of the risk is one way of finding out details about the level of risk that people or things are being exposed to. It can be very important to understand how much risk there is in carrying out a given process or some task or action. In various countries there are legal limits of risk exposure, above which, there can be prosecutions, even if
there hasn’t been an accident! The following purpose for having a safety case comes from the public inquiry into the Piper Alpha Oil Platform disaster [Cullen 1990]. Here it was stated that:
Primarily the safety case is a matter of ensuring that every company produces a formal safety assessment to assure itself that its operations are safe.
