Last edit: 16/10/2023
The book details how to perform Risk Reduction in machinery using Functional Safety techniques.
Three international standards cover the topic: ISO 13849-1, IEC 62061, and ISO 13849-2. The second edition of IEC 62061 was published in 2021, and the fourth edition of ISO 13849-1 was published in April 2023.
Most machines have hazards associated with their use. To achieve an acceptable level of safety, risk reduction measures must be taken. For example, glycol water can be used instead of oil in a forging press to eliminate the risk of fire; or fixed guards can be used to protect operators from hazardous movements within the machine. These measures have nothing to do with functional safety.
In other cases, it may be necessary to install an interlocking device that detects a hazardous situation: for example, a person accesses a hazardous area of the machine. In this case, when the movable guard is opened, all hazardous movements must be stopped. In other situations, a high-pressure switch is needed to detect a dangerous state: in this case, a valve must be closed to bring the process to a safe state. All that has just been described belongs to the world of Functional Safety; in other words, a safety function has just been defined and a safety control system must be designed to perform that specific function.
Both standards mentioned deal with functional safety requirements aimed at reducing the risk of injury or damage to the health of people in the vicinity of the machine and those directly involved in the use of the machine.
Whenever we rely on a control system to reduce a risk, the following question arises: What is the probability that the safety system will fail and thus the risk reduction measure will not work as intended? In other words, what is the probability that a compressor will not stop in the event of high pressure in a tank, or that a dangerous movement will not stop in a robotic cell when an access door is opened? This, again, is the field of functional safety.
The book aims to show that although there are two separate standards, there is a rather similar approach to functional machine safety. There still remain some differences, which will be described in detail in the book.