Glossary
Definitions are provided for educational clarity. Official definitions in legislation, contracts, or industry standards may differ. Terms marked rail-specific or legal term should not be read as universal UK law.
Biomathematical fatigue model
Section titled “Biomathematical fatigue model”Scope: general (research-based)
A mathematical method that estimates likely fatigue from a work pattern, using factors such as shift timing, sleep opportunity, cumulative load, and workload. Outputs are population-level modelled estimates — decision-support, not measures of real-time alertness. See biomathematical fatigue models.
Circadian rhythm
Section titled “Circadian rhythm”Scope: general
The internal biological cycle that regulates sleep and alertness over roughly 24 hours. Work against this cycle — particularly night work — can increase fatigue risk. See circadian rhythm and fatigue, fatigue management during night works, night shift fatigue, and timing and circadian effects in fatigue models.
Commute
Section titled “Commute”Scope: general
Regular travel between home (or a usual base) and the workplace. Commute time may affect overall fatigue burden even when it is not paid working time. See duty, travel, and commute.
Competent person
Section titled “Competent person”Scope: legal term (UK)
A person with sufficient training, experience, and knowledge to assess health and safety risks in context. Fatigue assessments and controls should be reviewed by competent persons — templates and checklists support review but do not replace competent judgement.
Checklist (fatigue)
Section titled “Checklist (fatigue)”Scope: general (this site)
A structured list of prompts to support review of a shift pattern, travel plan, or related fatigue factor. Checklists on this site are original and not reproduced from ORR or industry standards. They do not prove compliance. See shift pattern review checklist and door-to-door planning checklist.
Consecutive duties
Section titled “Consecutive duties”Scope: general
A sequence of worked shifts or days without adequate recovery. Cumulative fatigue often builds across consecutive duties. See consecutive shifts and recovery.
Door-to-door time
Section titled “Door-to-door time”Scope: general (fatigue planning concept)
Total elapsed time from leaving an origin to returning after work — typically including outward travel, the work period, and return travel. Definitions and policy use vary by sector. See door-to-door time and the door-to-door planning checklist.
Scope: general — definitions vary
The period of planned work at a site or operational location. What counts as duty — and whether travel is included — depends on employer policy, contract, and sector. See duty, travel, and commute.
Early start
Section titled “Early start”Scope: general
A shift beginning in early-morning hours when circadian alertness is typically low. See early starts and fatigue.
Employer duties
Section titled “Employer duties”Scope: legal term (UK) — general overview only
Statutory obligations on employers to manage health and safety risks, including fatigue where it is foreseeable. General duties arise under legislation such as HSWA and MHSWR — how they apply depends on context. See employer duties and fatigue risk. This site does not provide legal advice.
Exceedance
Section titled “Exceedance”Scope: rail-specific / organisational policy
A breach or predicted breach of a defined fatigue control or trigger threshold, treated as a governance event requiring documented review. Formal exceedance frameworks are common in rail contractual standards — they are not universal UK law.
Fatigue
Section titled “Fatigue”Scope: general
A state of reduced mental or physical performance resulting from factors including sleep loss, extended wakefulness, circadian rhythm disruption, and workload. See what is fatigue management?.
Fatigue assurance
Section titled “Fatigue assurance”Scope: general
The ongoing process of checking whether fatigue controls work in practice — through planned vs actual review, records, reporting trends, and management learning. See fatigue assurance and scenario guides such as maintenance work and emergency works.
Fatigue governance
Section titled “Fatigue governance”Scope: general
The rules, roles, thresholds, and recorded decisions used to control foreseeable fatigue risk — including who may approve elevated risk and what must be documented. See management accountability for fatigue, fatigue assurance, and fatigue records and audit.
Field operations
Section titled “Field operations”Scope: general
Work at physical operational locations away from a fixed office — including construction sites, utilities networks, highways maintenance, and mobile engineering teams. Fatigue drivers often include travel, changing sites, and limited welfare. See infrastructure and field operations fatigue, highways, and utilities and maintenance.
Audit trail
Section titled “Audit trail”Scope: general
A retained record of assessments, inputs, decisions, mitigations, and reviews at the time fatigue risk was considered. Supports learning and assurance — does not prove a shift was safe. See fatigue records and audit and the fatigue decision record template.
Fatigue Index (FI)
Section titled “Fatigue Index (FI)”Scope: model output (HSE RR446)
A score (typically 0–100) from HSE RR446-based methods estimating the modelled probability of very high sleepiness during a duty, linked to Karolinska Sleepiness Scale (KSS) levels 8–9. FI is not a legal limit. See FI vs RI, the FRI guide, and HSE RR446 explained.
Fatigue management
Section titled “Fatigue management”Scope: general
How organisations identify, assess, and control risks from tiredness, sleep loss, circadian disruption, and demanding work patterns.
Fatigue management plan (FMP)
Section titled “Fatigue management plan (FMP)”Scope: rail-specific / organisational
A documented plan describing how fatigue risk will be assessed and managed for specific roles, activities, or contracts. Common in rail and operational frameworks; terminology and requirements vary. See the fatigue management plan template and FRMS guide.
Fatigue risk assessment
Section titled “Fatigue risk assessment”Scope: general
A structured process to identify fatigue-related hazards, evaluate controls, and define further actions. See the fatigue risk assessment guide and assessment template.
Fatigue risk index (FRI)
Section titled “Fatigue risk index (FRI)”Scope: general term; HSE RR446 implementation
A roster-based scoring method estimating fatigue-related exposure from shift patterns. In the UK, widely referenced approaches build on HSE RR446. See fatigue risk index (FRI) and model inputs and outputs.
Fatigue risk management system (FRMS)
Section titled “Fatigue risk management system (FRMS)”Scope: general (common in transport and safety-critical sectors)
A documented, risk-based framework combining policy, assessment, roster controls, monitoring, and review to manage fatigue-related risk. See FRMS guide and ORR rail fatigue guidance explained for rail context.
Guidance
Section titled “Guidance”Scope: general
Practical publications from regulators or sector bodies that help dutyholders understand how to meet their duties. Guidance is not statute, though it may be influential. See law, guidance, standards and policy, HSG256 shift work guidance explained, and ORR rail fatigue guidance explained.
Fit for duty
Section titled “Fit for duty”Scope: general — use cautiously
Whether a worker is sufficiently alert and capable for safe work at a given time. Involves individual self-assessment, supervision, and organisational policy. This site does not provide medical or occupational health advice on fitness for duty.
Forward rotation
Section titled “Forward rotation”Scope: general
A shift rotation that moves from morning to afternoon to night shifts. Often discussed in shift work guidance as potentially easier to adapt to than backward rotation — but optimal design depends on the operation.
HSE RR446
Section titled “HSE RR446”Scope: HSE research report
HSE Research Report RR446, The development of a fatigue / risk index for shiftworkers (2006) — the public research source behind UK fatigue and risk index methods. It is research guidance, not a legal compliance threshold. See HSE RR446 and the fatigue risk index.
Human factors
Section titled “Human factors”Scope: general
How people interact with tasks, equipment, organisations, and their environment — including fatigue as a work-system design issue. See human factors and fatigue.
Industry standard
Section titled “Industry standard”Scope: sector / contractual
A standard developed for use within a particular industry or supply chain — often imposed by contract rather than applying as universal UK law. See law, guidance, standards and policy.
Job and breaks component
Section titled “Job and breaks component”Scope: model component (HSE RR446)
The part of a fatigue model reflecting workload/job demand and within-shift breaks, alongside the timing and cumulative components. See workload, breaks and fatigue models.
Karolinska Sleepiness Scale (KSS)
Section titled “Karolinska Sleepiness Scale (KSS)”Scope: general (research / model link)
A nine-point subjective sleepiness scale. In HSE RR446-based methods, the Fatigue Index relates to high sleepiness levels (KSS 8–9).
Legislation
Section titled “Legislation”Scope: legal term (UK)
Law made by Parliament (or devolved legislatures) that creates legal duties. Fatigue-related duties often arise under general health and safety legislation rather than detailed roster rules in statute. See law, guidance, standards and policy.
Management accountability
Section titled “Management accountability”Scope: general
Clear ownership for fatigue-related planning, review, and escalation — including documented decision-making by competent persons. See management accountability for fatigue and the fatigue decision record template.
Mitigation
Section titled “Mitigation”Scope: general
A control measure applied when fatigue risk is elevated but work proceeds under documented management acceptance — for example adjusted tasks, additional supervision, or recovery planning. Record mitigations using the fatigue decision record template.
Decision record (fatigue)
Section titled “Decision record (fatigue)”Scope: general (this site)
A structured record of the reasoning behind a fatigue-related management decision — context, risk factors, mitigations, accountability, and follow-up. It records the basis for review; it does not prove work was safe or guarantee compliance. See fatigue decision record template.
Night work
Section titled “Night work”Scope: general — definitions vary
Work during biological night or circadian low periods. Definitions differ between working time law, organisational policy, and fatigue models. See night shift fatigue and night workers and fatigue risk.
Night worker
Section titled “Night worker”Scope: general — legal and policy definitions vary
A worker who performs night work as defined by working time law, organisational policy, or operational practice. Night-worker provisions in the Working Time Regulations are not the same as fatigue model outputs. See night workers and fatigue risk.
Organisational policy
Section titled “Organisational policy”Scope: general
Internal rules set by an employer — for example roster limits, overtime approval, fatigue reporting, or model trigger levels. Policies may be stricter than minimum legal requirements but cannot lawfully reduce statutory protections. See organisational policy thresholds and law, guidance, standards and policy.
Planned fatigue vs actual fatigue
Section titled “Planned fatigue vs actual fatigue”Scope: general
Planned fatigue is exposure assessed at roster design stage; actual fatigue reflects worked hours and operational deviations. Both may need monitoring. See planned vs actual fatigue.
Probabilistic model
Section titled “Probabilistic model”Scope: general
A model whose outputs express likelihoods or relative risks — not certainties about a specific individual or incident. See limitations of fatigue models.
Quick return
Section titled “Quick return”Scope: general
A short rest period between the end of one shift and the start of the next. Often associated with insufficient sleep opportunity. Local definitions and policy thresholds vary. See quick return shifts and fatigue and consecutive shifts and recovery.
Reasonably practicable
Section titled “Reasonably practicable”Scope: legal term (UK)
The statutory test for health and safety duties — balancing risk against the cost, time, and trouble of controls. Employers must manage fatigue risk so far as is reasonably practicable where it is foreseeable.
Reference schedule
Section titled “Reference schedule”Scope: model output (HSE RR446)
A baseline shift pattern used to normalise Risk Index comparisons. RI values are meaningful relative to this reference, not as absolute accident probabilities.
Working time
Section titled “Working time”Scope: legal term (UK) — general overview only
Statutory provisions on hours, rest, breaks, and night work — principally the Working Time Regulations 1998 in Great Britain, with sector exemptions. Working time compliance is not the same as fatigue risk management. See working time compliance vs fatigue management.
Rest period
Section titled “Rest period”Scope: general — legal and policy definitions vary
Off-duty recovery time between shifts. Minimum rest requirements depend on role, sector, and applicable working time rules — with exemptions in some contexts. See recovery periods and fatigue and consecutive shifts and recovery.
Rest break (within shift)
Section titled “Rest break (within shift)”Scope: general
A pause or break taken during a duty period. Frequency, length, and whether breaks occur in practice affect within-shift fatigue. See breaks and recovery during shifts.
Cumulative fatigue
Section titled “Cumulative fatigue”Scope: general
Fatigue that builds across consecutive shifts, short recovery periods, or repeated demanding patterns. Modelled in HSE RR446 cumulative components and operational experience. See sleep debt and fatigue, consecutive shifts and recovery, and cumulative fatigue in models.
Risk Index (RI)
Section titled “Risk Index (RI)”Scope: model output (HSE RR446)
A relative multiplier comparing modelled accident/incident risk for a duty or pattern to a reference schedule. RI = 1.0 is the reference level; higher values indicate elevated relative modelled risk. RI does not prove a shift is unsafe. See FI vs RI and HSE RR446 explained.
Roster / roster design
Section titled “Roster / roster design”Scope: general
The planned pattern of shifts for workers over a period. Roster design is a primary lever for fatigue control. See roster design principles and the shift pattern review checklist.
Safety-critical work
Section titled “Safety-critical work”Scope: general
Work where fatigue-related error could directly lead to serious harm — common in transport, healthcare, utilities, and process industries. See safety-critical work and fatigue.
Self-reporting
Section titled “Self-reporting”Scope: general
Workers reporting fatigue, impaired alertness, or concerns about coping with work through agreed channels. Reporting culture is part of wider FRMS governance. See worker fatigue reporting.
Shift work
Section titled “Shift work”Scope: general
Work schedules outside a conventional daytime pattern, including rotating, permanent night, and extended shifts. See shift work fatigue.
Sleep debt
Section titled “Sleep debt”Scope: general
Accumulated shortfall between sleep needed and sleep obtained — often building across consecutive duties, night blocks, and disrupted rest. See sleep debt and fatigue.
Task demand
Section titled “Task demand”Scope: general
The mental and physical workload of duties — including peaks, high-consequence decisions, and break feasibility. See task demand and workload fatigue and workload, breaks and fatigue models.
Vigilance work
Section titled “Vigilance work”Scope: general
Sustained attention tasks such as monitoring, control room work, or safety-critical observation — where fatigue can reduce detection of change. See vigilance work and fatigue.
Travel (outbound / return)
Section titled “Travel (outbound / return)”Scope: general
Journey time to and from a work location. May contribute to fatigue burden separately from paid duty. See duty, travel, and commute.