When a machine meets the EHSR requirements of the Machinery Directive 2006/42/EC and has undergone the necessary upgrades and modifications according to harmonized standards, we can generally consider the machine to be safe. But is this really the case?
Imagine a machine equipped with an emergency stop button, safety doors with safety interlocks, and even components like a grating scanner. All these safety features meet the Performance Level ( PLr ) requirements of the risk assessment. However, the process this machine handles involves parameters such as pressure, temperature, and flow rate, and the media it processes are hazardous chemicals. In this situation, simply completing the risk assessment and corresponding risk reduction based on the machine's instructions does not guarantee true safety. The solution to this problem is Process Safety Management ( PSM ).
"Process safety management refers to the application of management principles and systems to identify, understand, and control process hazards in order to prevent process-related injuries and accidents." — From CCPS ( Center for Chemical Process Safety ). Process safety management (PSM) involves 14 key elements, among which process hazard analysis ( PHA ) corresponds to mechanical safety risk assessment , and the method used is hazard and operability analysis (HAZOP ).
Hazop originated in the UK and was invented by chemical engineer T. Clays. It was first used in a newly built phenol plant of Imperial Chemical Industries in 1963 , and was only widely adopted after 10 years of internal testing and application within the company.
HAZOP has the following three main characteristics:
First, collective wisdom: Achieving collective wisdom through review meetings. Analysis teams composed of individuals with diverse knowledge backgrounds from various relevant disciplines work together.
Second, using guiding words to stimulate innovation: Combining common parameters, using guiding words to identify deviations and reveal the accident scenario, that is, identifying the possible scenarios, causes, hazards, and consequences of the accident. For example:
Third, systematic and structured review: traverse all components of the process, use all feasible guiding words, and identify and analyze risks from deviations in two-way reasoning.
It's easy to see that a successful HAZOP analysis requires a diverse team of personnel with varying backgrounds and expertise. This team includes, but is not limited to: the organizer, the HAZOP analysis chair, a secretary or recorder, a process engineer (theoretical lead), a process control / instrumentation engineer, a safety engineer, an equipment / mechanical engineer, an operations expert (operations lead), and a patent holder or supplier (if needed).
People with different knowledge backgrounds and specialties working together are more creative and can identify more problems than working alone; all accident conditions are deviations from normal operation and from the basic state specified in the design that exceed the control range, which will cause problems or dangers.
In summary, we can draw some conclusions about the advantages and disadvantages of HAZOP:
Time-consuming, labor-intensive, and costly;
Ø "Brainstorming": Conducted by an analytical team, covering processes, equipment, instruments, operations, and safety;
It is the most systematic and comprehensive method among the many methods of process hazard analysis ( PHA ), and it can identify potential hazards in the system;
The core (essence) of HAZOP analysis is to identify the plot of an incident;
The principle is simple, but doing it well is not easy: it is a requirement that cannot be achieved through self-study; it also places high demands on the HAZOP chairperson.
