There is an inherent risk associated with every activity that we undertake on a daily basis, for me examples of these could be walking to work, working in the laboratory, going shopping, even sitting here in the office writing this post at my desk (the building may catch fire for example).
As a society we mitigate these risks in a number of different ways, sometimes the risk is just acceptable, or tolerable, to us as individuals, such as for me walking to work is about as safe as I can make it and I accept the risk. For other activities safeguards are put in place to reduce the risks to a tolerable level.
Taking the example of my office catching fire, a number of different safeguards are put in place to protect me and the hundreds of others that share the building, some of these passive and some active such as good building design giving clear and regular escape routes, frequent placement of fire extinguishers, an alarm system and emergency exit lighting.
As a system these work together to bring the probability of the users of this building coming to harm in the event of a fire down to a level that is considered to be acceptable to the building owners as they could be liable in the event of an accident occurring.
In other situations safeguards are put in place to protect employees, the public and the environment from death, injury or damage, for example in control of industrial processes where failure could result in a serious incident with loss of life and damage to the environment. The chances are you are surrounded by things that protect you on a daily basis without you even knowing it (even good road design and traffic lights play a part in keeping my walk to work safe).
Increasingly these safeguard functions are provided by electrical and electronic systems, in the case of my office, in the event of a fire an electronic system detects it and triggers emergency lighting to guide me and others quickly and safely to the nearest emergency exit. For industrial processes sensors may identify potentially unsafe situations and cause the process to be shut down before it can escalate into a dangerous event.
The thing to consider with electrical and electronic safety critical systems is that their safety doesn’t just happen by accident; it is a result of good design practices and methodology both to avoid faults in the system and also provide a level of tolerance, this is supported by an effective quality management system focussed on achieving the required level of risk reduction and, importantly, reliability in the system. Critically, this covers the entire lifecycle of the product as, for example, poor maintenance can result in a system failing to act when needed.
To put this in context, the people who specified the emergency lighting system that is used in this building did so to reduce the risk of me and other users coming to harm in a fire. They probably spent a great deal of time, effort and money to do this. They (and I) want to be assured that in the event of a fire the emergency lighting system will work exactly as intended when needed and the system will activate and guide me to safety.
This is where functional safety comes in. The assessment that is performed checks that the system is designed in a way that can withstand a given number of faults without failing in a way that renders it dangerous or inoperative and that software used is designed to avoid systematic errors, as the risk reduction required gets higher, the level of protection in the system also increases and stricter measures may need to be incorporated. This takes into consideration the application and use of the product and even things like maintenance routines as, for example, if you don’t routinely change batteries in a battery back-up system you can’t necessarily expect that it will work as expected in 15 years’ time. The result of this is that the manufacturer’s declared level of safety and reliability for their product can be validated and shown to provide the level of risk reduction that they claim over the life of the product.
This is hugely important when selecting a system to protect your employees, the public or environment as if you are investing in their safety you want to make sure you are getting exactly what you specified.
And, as I sit in the office typing this, I too want to have the peace of mind that the systems in place to protect me in the rare event that they are needed will do so exactly as intended.
For further information on Functional Safety please email Paul Turner.
Author: Paul Turner
Certification Technical Expert, Gas & Electrical Products