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Industrial risk assessment

Industrial Maintenance and Reliability Engineering Risk Assessment: Defects, Isolation and Spares Controls

A worked example of how a maintenance and reliability team finds, scores and controls the risks that threaten plant availability, people and the integrity of critical equipment, from specification mismatch to isolation errors.

Updated November 2026 8 hazards assessed Review every 6 months Highest risk: Critical to Medium
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Executive summary

This assessment shows how a maintenance and reliability function can find, rate and control the risks that threaten plant availability, people and asset integrity. Eight risks were chosen because they are plausible in everyday plant maintenance and reliability work. Isolation errors and arc flash carry the highest harm, while specification mismatch, deferred maintenance and single sourced spares are the most likely to cause repeated losses. Each risk is scored before controls and again after existing and added controls. Most risks fall to Medium or Low once the added controls are in place, but isolation and energized work stay at a level that needs senior attention. The first actions are a written isolation plan with an independent zero energy check, a ranked maintenance backlog and a second source for critical spares. The plant is a teaching example, so every score illustrates method, not a real organization.

Focus area
Industrial maintenance and reliability engineering
Setting
Maintenance and reliability function of a process plant with rotating, electrical and instrumented equipment
Method
Five by five likelihood and severity register with inherent and residual scoring

Scope

This assessment covers planned and corrective maintenance, reliability analysis, spares and contractor work on critical equipment, from specification and installation through inspection and retirement. It looks at risks to people, availability, asset integrity and the environment. It does not describe a real plant, a named asset or any specific legal regime. Site layout, jurisdiction, equipment make and the maintenance software in use are assumptions made for teaching, and each one must be replaced with site facts in a formal assessment.

Context

The example plant has a maintenance planning team, a reliability engineer, electrical and mechanical technicians, a stores team and contractors for major overhauls. Critical assets include pumps, compressors, motors, switchgear and process instruments. Work is planned in a computerized maintenance system, condition data comes from vibration, temperature and oil sampling routes, and spares are bought through approved suppliers. Each risk is scored before controls to show its natural level, then again after the existing controls and the additional controls proposed.

Objectives, assets and stakeholders

The objective is to keep critical equipment available and safe, to prevent harm to people and the environment, and to protect the integrity of assets over their life. The assets in scope are rotating equipment, switchgear, process instruments, lubrication systems, spares stock, condition data and the maintenance records that hold them. Stakeholders include maintenance technicians, electricians, reliability engineers, planners, stores staff, contractors, plant operators, the plant manager and the environmental and safety functions. Clear roles matter: every risk has one owner role, and the maintenance planning manager reviews the register each month and reports to the plant manager each quarter.

Risk matrix: before and after controls

Each cell shows hazard numbers placed by likelihood and impact. Compare the two grids to see how controls move each hazard.

Before controls

Inherent risk

Risk before controls: rows are likelihood from almost certain to rare, columns are impact from insignificant to catastrophic. Cells list hazard numbers.
1
Insignificant		 2
Minor		 3
Moderate		 4
Major		 5
Catastrophic
5 Almost certain
4 Likely Likelihood 4, impact 3, score 12, high: H02 H08 Likelihood 4, impact 4, score 16, high: H01 Likelihood 4, impact 5, score 20, critical: H03
3 Possible Likelihood 3, impact 3, score 9, medium: H04 H05 Likelihood 3, impact 4, score 12, high: H07
2 Unlikely Likelihood 2, impact 5, score 10, high: H06
1 Rare

After controls

Residual risk

Risk after controls: rows are likelihood from almost certain to rare, columns are impact from insignificant to catastrophic. Cells list hazard numbers.
1
Insignificant		 2
Minor		 3
Moderate		 4
Major		 5
Catastrophic
5 Almost certain
4 Likely
3 Possible
2 Unlikely Likelihood 2, impact 2, score 4, low: H04 H05 Likelihood 2, impact 3, score 6, medium: H01 H02 H07 H08 Likelihood 2, impact 4, score 8, medium: H03
1 Rare Likelihood 1, impact 4, score 4, low: H06
  • Low 1 to 4
  • Medium 5 to 9
  • High 10 to 16
  • Critical 17 to 25

Hazard register

A summary first, then the detail for each hazard.

Summary of hazards with scores before and after controls
No.HazardBeforeAfterOwner
H01 Specification mismatch and defective replacement parts 16 High 6 Medium Stores and procurement lead
H02 Deferred and poorly planned preventive maintenance 12 High 6 Medium Maintenance planning manager
H03 Lockout and isolation error during intrusive work 20 Critical 8 Medium Plant safety lead
H04 Condition monitoring gaps and weak failure analysis 9 Medium 4 Low Reliability engineer
H05 Lubricant and chemical exposure with spills 9 Medium 4 Low Environmental compliance officer
H06 Electrical energized work and arc flash 10 High 4 Low Electrical maintenance supervisor
H07 Dependence on a single critical spares supplier 12 High 6 Medium Procurement manager
H08 Procedural deviation and competence gaps 12 High 6 Medium Maintenance supervisor
H01

Specification mismatch and defective replacement parts

Supplier Before 16 After 6

A replacement part is bought against an outdated or incomplete specification, or arrives out of tolerance, and is fitted without a check, so the equipment fails early or performs poorly.

Who or what is affected: Maintenance technicians, plant operators and production schedules

Causes

Old part numbers in the system, substitutions made without review and suppliers who change materials without notice.

Consequences

Premature failure, unplanned shutdown, repeat repair costs and damage to connected equipment.

Existing controls

  • Spares are bought from approved suppliers who provide a certificate of conformity.
  • Goods are checked against the purchase order on receipt.

Control gaps

Certificates are filed but never compared with drawings, and substitutions are not recorded against the asset.

Additional controls

  • Prevent: Write a specification for each critical spare and have the reliability engineer approve it before purchase.
  • Detect: Inspect and measure a sample of incoming critical spares against drawings before they are fitted.
Likelihood 4 x impact 4 before; 2 x 3 after Owner: Stores and procurement lead Target: Within 60 days Early warning: Repeat failure of a part within its expected life after a new supplier or substitute is used.
H02

Deferred and poorly planned preventive maintenance

Operational Before 12 After 6

Preventive tasks on critical assets are pushed back again and again because of production pressure, and the backlog grows until a failure occurs that a planned task would have prevented.

Who or what is affected: Plant operators, maintenance crews and production managers

Causes

Production targets that outrank maintenance, weak links between condition data and work orders, and short outages.

Consequences

Unplanned breakdowns, higher repair cost, longer outages and pressure to run equipment beyond its safe limits.

Existing controls

  • Preventive tasks are listed in the maintenance system with set intervals.
  • The backlog is reviewed at the weekly planning meeting.

Control gaps

Deferrals are approved without a stated end date, so they roll forward without review.

Additional controls

  • Prevent: Rank the backlog by asset criticality and remove tasks that no longer apply to the equipment.
  • Respond: Escalate overdue tasks on critical assets to the plant manager with a short written risk note.
Likelihood 4 x impact 3 before; 2 x 3 after Owner: Maintenance planning manager Target: Within 45 days Early warning: Overdue preventive tasks on critical assets above an agreed count for two consecutive weeks.
H03

Lockout and isolation error during intrusive work

Safety Before 20 After 8

Equipment is opened or worked on while stored energy or a live supply remains, because the isolation is incomplete, the wrong point is locked or the zero energy test is skipped.

Who or what is affected: Maintenance technicians, contractors and nearby operators

Causes

Complex isolation layouts, time pressure, unclear labelling and contractors who were not briefed on the local system.

Consequences

Serious injury or death, equipment damage, prosecution risk and loss of trust in the maintenance function.

Existing controls

  • A permit to work is issued for all hazardous jobs.
  • Personal lockout devices are fitted at each isolation point.

Control gaps

Zero energy tests are recorded as done without a named tester, and permits are not checked after shift changes.

Additional controls

  • Prevent: Require a written isolation plan and an independent check of zero energy before any intrusive work starts.
  • Detect: Audit a sample of permits each month against the isolation certificate and the physical lock positions.
Likelihood 4 x impact 5 before; 2 x 4 after Owner: Plant safety lead Target: Within 14 days Early warning: A permit closed without a recorded zero energy test or with a lock removed by someone other than its owner.
H04

Condition monitoring gaps and weak failure analysis

Technology and data Before 9 After 4

Vibration, temperature and oil data are missing, wrongly set up or ignored, and failures are recorded without cause, so the reliability programme cannot learn from past events.

Who or what is affected: Reliability engineers, planners and asset owners

Causes

Sensors that drift, routes missed during outages, and failure codes that are chosen for convenience.

Consequences

Missed early warnings, repeat failures, poor spares planning and wrong maintenance intervals.

Existing controls

  • Vibration and temperature readings are logged on each route.
  • Failures are recorded in the maintenance system with a short description.

Control gaps

Alarm limits are set once at installation and never reviewed, and failure causes are often left blank.

Additional controls

  • Detect: Review trend alarms weekly and confirm alarm limits against the equipment supplier data.
  • Recover: Run a root cause review after each critical failure and update the failure record with findings.
Likelihood 3 x impact 3 before; 2 x 2 after Owner: Reliability engineer Target: Within 90 days Early warning: A gap of more than one week in route data on a critical asset, or failure records with no cause code.
H05

Lubricant and chemical exposure with spills

Environmental Before 9 After 4

Oils, greases, cleaning solvents and hydraulic fluids are stored, handled or topped up carelessly, so leaks reach drains, soil or the workforce.

Who or what is affected: Maintenance staff, neighbouring communities and the local environment

Causes

Open containers, rushed top ups, damaged seals and drains that are not mapped.

Consequences

Ground contamination, skin and respiratory exposure, fines and a clean up cost.

Existing controls

  • Oil and chemicals are stored in labelled, bunded containers.
  • Spill kits are placed near lubrication points.

Control gaps

Drain routes are not marked on the site plan, and spill kit contents are not checked.

Additional controls

  • Prevent: Replace open oil containers with sealed dispensing and limit the quantity held at each work area.
  • Respond: Practice a spill response drill for lubrication and hydraulic work twice a year.
Likelihood 3 x impact 3 before; 2 x 2 after Owner: Environmental compliance officer Target: Within 60 days Early warning: Leaks or drips found on routine rounds at the same location twice within a month.
H06

Electrical energized work and arc flash

Safety Before 10 After 4

Switchgear or motor control panels are opened or tested while energized, and an arc fault releases heat, light and pressure that can injure anyone nearby.

Who or what is affected: Electrical technicians, operators and visitors near switchrooms

Causes

Pressure to avoid outages, worn panel covers and tools that are not rated for the voltage.

Consequences

Severe burns, hearing damage, electrocution and a long outage after the fault.

Existing controls

  • Only authorized electricians may open switchgear.
  • Arc rated clothing is issued for panel work.

Control gaps

Method statements are not updated after panel changes, and clothing ratings are not checked against the fault level.

Additional controls

  • Prevent: Allow energized work only with a written method statement, approved tools and a second competent person present.
  • Recover: Keep first aid and rescue equipment for electrical injuries at each switchroom entrance.
Likelihood 2 x impact 5 before; 1 x 4 after Owner: Electrical maintenance supervisor Target: Within 30 days Early warning: Energized work requested without a written method statement or a panel cover found removed.
H07

Dependence on a single critical spares supplier

Supplier Before 12 After 6

A key bearing, seal or drive component comes from one supplier, and a delay, insolvency or quality problem leaves critical equipment without a replacement.

Who or what is affected: Plant availability, production planners and maintenance teams

Causes

Cost saving through single sourcing, specialist parts and long lead times for custom items.

Consequences

Extended outages, expediting cost, emergency substitutions and possible safety compromise.

Existing controls

  • A critical spares list is kept by the stores team.
  • Two suppliers are qualified for most bearings.

Control gaps

The critical spares list is not reviewed against current equipment, and supplier health is checked only at contract renewal.

Additional controls

  • Prevent: Qualify a second source for each single-source critical spare and hold agreed safety stock.
  • Detect: Review supplier delivery performance each month against the agreed lead time.
Likelihood 3 x impact 4 before; 2 x 3 after Owner: Procurement manager Target: Within 90 days Early warning: Lead time for a critical spare rising above the agreed level or a supplier missing two deliveries in a row.
H08

Procedural deviation and competence gaps

People Before 12 After 6

Technicians skip steps in work instructions, rely on memory or take shortcuts, and new staff are given tasks before they are competent, so errors reach the equipment.

Who or what is affected: Maintenance technicians, supervisors and the equipment they work on

Causes

Work instructions that are out of date, production pressure, and shadowing that ends before skills are proven.

Consequences

Incorrect torque or alignment, contamination, wrong reassembly and repeat failure.

Existing controls

  • Work instructions exist for the main maintenance tasks.
  • New technicians shadow a senior technician for a set period.

Control gaps

Competence is recorded at induction only, and deviations are corrected informally without a record.

Additional controls

  • Respond: Pause a job when a step is skipped and require a recorded review before work restarts.
  • Prevent: Check competence against each task type and renew it every year.
Likelihood 4 x impact 3 before; 2 x 3 after Owner: Maintenance supervisor Target: Within 60 days Early warning: Work orders closed with a missing step, a late sign off or a repeat rework on the same asset.

Rating method and evaluation

Each risk is rated on two five point scales. Likelihood runs from Rare to Almost certain, and severity runs from Negligible to Catastrophic. Multiplying the two gives a score from 1 to 25, which falls into one of four bands: Low from 1 to 4, Medium from 5 to 9, High from 10 to 16 and Critical from 17 to 25. The score is a guide for ordering work, not a measurement. Inherent risk is the score before any controls. Residual risk is the score after the existing and added controls, and it must never be higher than the inherent score. Severity considers harm to people first, then environmental release, asset damage, lost production and reputation. A safety risk is never rated down only because it has not happened yet. Anything still Critical or High needs senior attention and a dated plan, anything Medium needs routine controls with a named owner, and anything Low is accepted and watched. Technicians and supervisors should challenge every rating, and ratings are reviewed whenever an indicator reaches its threshold or after a failure.

Likelihood, impact and rating bands

Likelihood

  • 5 Almost certain: Expected to happen in most circumstances.
  • 4 Likely: Will probably happen in many circumstances.
  • 3 Possible: Could happen at some time.
  • 2 Unlikely: Not expected, but it could happen.
  • 1 Rare: Only in exceptional circumstances.

Impact

  • 1 Insignificant: No lasting effect. Handled within routine work.
  • 2 Minor: Small effect that is quickly corrected.
  • 3 Moderate: Noticeable effect that needs managed effort to correct.
  • 4 Major: Serious effect on people, delivery or reputation.
  • 5 Catastrophic: Severe or lasting effect that threatens the whole activity.

Bands (likelihood x impact)

  • Low (1 to 4): Accept and monitor.
  • Medium (5 to 9): Manage with routine controls.
  • High (10 to 16): Senior attention and a treatment plan.
  • Critical (17 to 25): Act first. Do not proceed until reduced.

Monitoring, escalation and review

Review this assessment every 6 months, and sooner when an indicator below reaches its threshold.

Early-warning indicators and escalation thresholds
Indicator to watchEscalate when
Permits closed without a recorded zero energy test or with a lock removed by someone other than its owner.Escalate to the plant safety lead at once and stop the affected work until the isolation is confirmed.
Overdue preventive tasks on critical assets above an agreed count for two consecutive weeks.Escalate to the maintenance planning manager, and to the plant manager if the count is not reduced within a week.
Repeat failure of a part within its expected life after a supplier or substitute is used.Escalate to the stores and procurement lead within two days, and hold further purchases of that part until reviewed.
Lead time for a critical spare rising above the agreed level or a supplier missing two deliveries in a row.Escalate to the procurement manager and activate the second source where one is qualified.
Leaks or drips found at the same location twice within one month.Escalate to the environmental compliance officer and isolate the source until repaired.

Contingency arrangements

If a serious event occurs, such as an injury during isolation, an electrical fault or a major leak, the plant safety lead stops the work, secures the area and makes sure first aid and emergency services are called. The maintenance planning manager records the affected assets and suspends related tasks. Stores checks alternative sources for any failed critical part, and the environmental officer contains and reports any release as required locally. Operators are told what to expect and how long the outage may last.

Prioritized action plan

  1. Introduce a written isolation plan with an independent zero energy check for all intrusive work, owner plant safety lead, within 14 days.
  2. Ban energized work without a written method statement and a second competent person, owner electrical maintenance supervisor, within 30 days.
  3. Rank the preventive maintenance backlog by criticality and set an end date for every deferral, owner maintenance planning manager, within 45 days.
  4. Write and approve specifications for critical spares and check incoming parts against drawings, owner stores and procurement lead, within 60 days.
  5. Qualify a second source for single sourced critical spares and review supplier performance monthly, owner procurement manager, within 90 days.

Conclusion

Reliable plant depends on a few steady habits: written isolation plans, independent checks, a ranked backlog, reviewed alarm limits and a second source for critical spares. The highest scores sit with isolation, energized work and specification mismatch, and each has actions that bring the residual score down. Treat the register as a living record, review it on the stated cycle and seek qualified engineering and safety advice for any real plant decision.

Assumptions and limitations

Assumptions

  • The plant operates a computerized maintenance system with asset criticality ratings already assigned.
  • Technicians are trained for their tasks, but competence records are incomplete and are used here as a teaching gap.
  • Jurisdiction is not specified, so legal duties are described only in general terms.

Limitations

  • The scores are examples for learning and do not describe any real plant, asset or incident.
  • Electrical, pressure and hazardous substance rules differ by location and change over time, so specialist review is needed.
  • This is educational content and does not replace a formal site-specific assessment or licensed engineering advice.

Related frameworks to study

  • Reliability-centered maintenance logic
  • Failure mode and effects analysis
  • Hierarchy of controls
  • Lockout and isolation practice with permit to work

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For Learning Reference Only: This assessment demonstrates how risk assessment principles are applied in a practical setting, providing a useful reference for learning and understanding. Actual assessments may be adapted to suit specific site conditions and circumstances.

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