NEBOSH PSM key terms

A structured management system of policies and procedures aimed at preventing major accidents involving hazardous substances or energy, by controlling releases, fires and explosions rather than personal injury alone.

A hazard arising from loss of containment or uncontrolled energy that could cause multiple fatalities, serious injury, significant environmental damage or major asset loss, often beyond the site boundary.

The organised set of policies, responsibilities, procedures and resources an organisation uses to control risk, covering policy, planning, implementation, checking and management review in a continuous cycle.

The shared values, attitudes and behaviours of an organisation towards controlling major accident hazards, shown in leadership commitment, openness, challenge of unsafe conditions and learning from failure.

Visible commitment by managers and supervisors to process safety, demonstrated through setting expectations, providing resources, visiting the plant and reinforcing safe behaviour through their own actions.

A structured questionnaire used to measure workforce perceptions of safety priorities, communication, leadership and reporting, providing an indicator of culture and early warning of weakening safety performance.

The principle that risk should be reduced as low as reasonably practicable, balancing the cost, effort and time of further controls against the reduction in risk they would achieve.

A source of potential harm, such as a flammable liquid, toxic gas, high pressure or stored energy, which has the potential to cause injury, damage or environmental harm if uncontrolled.

The combination of the likelihood of a hazardous event occurring and the severity of its consequences, often expressed qualitatively as high, medium or low or quantitatively as a numerical value.

The systematic process of identifying hazards, evaluating the likelihood and consequences of harm, and deciding whether existing controls are adequate or further measures are needed.

A structured team exercise that systematically identifies hazards in a process or activity, often using checklists, guidewords or experience, before any detailed risk evaluation takes place.

Hazard and Operability study: a structured team technique that applies guidewords such as no flow, more or less to process parameters to identify deviations, their causes, consequences and safeguards.

A diagrammatic risk tool that places a top event at the centre, showing threats and preventive barriers on one side and consequences and mitigating barriers on the other.

A grid used to rank risk by combining categories of likelihood and consequence, giving a visual basis for prioritising controls and deciding whether risk is tolerable.

The process of dividing a site into zones according to the likelihood and duration of a flammable atmosphere, so that suitable electrical and other equipment can be selected.

Design philosophy that eliminates or reduces hazards by using smaller inventories, less hazardous materials, lower pressures and simpler processes, rather than relying on added control measures.

Applying the principles of minimise, substitute, moderate and simplify during process design so that hazards are removed or reduced at source and cannot be lost through maintenance failures.

Independent and successive safeguards, such as design, control systems, alarms, relief devices, physical containment and emergency response, that prevent or mitigate a hazardous event.

An instrumented system, including sensors, logic solvers and final elements, designed to bring a process to a safe state when a hazardous condition occurs, rated by its safety integrity level.

A discrete rating, usually one to four, expressing the required reliability of a safety instrumented function in reducing risk, with higher levels demanding lower probability of failure on demand.

A protective arrangement of relief valves, rupture discs, flare or vent lines designed to safely discharge excess pressure from equipment before it fails, protecting people and plant.

A formal procedure ensuring that changes to equipment, processes, materials, procedures or organisation are assessed for risk and authorised before implementation, with documentation and training updated.

A verification carried out before introducing hazardous materials or energy into new or modified plant, confirming construction, procedures, training and safety systems meet design requirements.

A structured check that plant, people, procedures and emergency arrangements are fully prepared before a major start-up or restart, identifying gaps to be closed before operation begins.

The documented technical data needed to understand and control process hazards, including chemicals, technology, equipment, piping and instrumentation diagrams, and safe operating limits.

Written, step-by-step instructions describing how to safely start, operate, shut down and handle abnormal situations in a process, including defined safe operating limits and required actions.

The defined ranges of key process parameters such as temperature, pressure and flow within which the plant can be run safely, with actions specified when limits are approached or exceeded.

The practices and training that help operators recognise, diagnose and respond to unusual process conditions before they escalate into loss of control or a major accident.

The combination of knowledge, skills and experience, evidenced and maintained through training and assessment, that enables a person to perform a task safely and reliably.

The study of how people interact with equipment, procedures and their working environment, used to design tasks and interfaces that reduce error and support reliable performance.

A failure in human performance such as a slip, lapse, mistake or violation, often influenced by workplace design, workload and procedures rather than by carelessness alone.

An activity where human failure could directly cause or fail to prevent a major accident, requiring particular attention to competence, procedures, supervision and error recovery.

The discipline of designing, rationalising and maintaining alarm systems so that operators receive clear, prioritised and manageable warnings, avoiding alarm flooding during upsets.

A formal documented system that authorises specific high-risk work such as hot work or confined space entry, confirming hazards are identified and controls are in place before work begins.

A documented set of arrangements describing how an organisation will detect, respond to, control and recover from incidents, including roles, resources, communication and evacuation.

A planned simulation or drill used to test emergency plans, communications and response capability, revealing weaknesses to be corrected before a real event occurs.

The unintended release of a hazardous substance or energy from its containment, such as a pipe, tank or vessel, which is the starting point for most major process accidents.

A physical, technical, procedural or human safeguard that prevents a threat from causing a top event or limits the consequences once the event has occurred.

A structured process for gathering evidence and analysing the immediate and underlying causes of an incident, so that recommendations prevent recurrence and learning is shared.

A set of analytical techniques, such as fault tree or five-whys, used to trace an incident beyond immediate causes to the underlying management and organisational failures that allowed it.

A proactive measure of process safety performance, such as overdue inspections or alarm rates, that gives early warning of deteriorating control before an accident occurs.

A measure of past outcomes, such as incident rates, releases or injuries, that shows whether performance has been poor but does not predict future failure.

A planned, independent check that process safety management arrangements are actually implemented and effective, providing evidence to management that controls are working as intended.

An organisation that systematically captures lessons from incidents, audits and near misses, shares them widely and changes practices so that experience improves future safety performance.