Glossary
Maintenance, reliability and EHS glossary
This glossary gives plain definitions of the maintenance, reliability, quality and safety terms used across this site, with the formula wherever there is one. It helps planners, reliability engineers, quality heads and EHS heads use the same words for the same things.
- API access
- A token-authenticated way for another system to read and write maintenance records, such as work orders, assets, breakdowns and machine readings, inside one organization. In MaintenanceIQ this is API access. The system that needs the data calls MaintenanceIQ.
- Asset criticality
- A rating of how much an asset's failure would affect safety, production, quality or cost. Many plants use three classes, such as A, B and C. Criticality decides PM frequency, which spares to stock and which work comes first.
- Availability (OEE)
- The share of planned production time that a machine actually runs. It is the OEE factor that breakdowns, changeovers and slow repairs pull down most.
Availability = Run time / Planned production time - Backlog
- Identified, approved maintenance work that has not been done yet, often measured in crew-weeks. A visible backlog can be planned. An invisible one turns into firefighting.
- Bad actor
- An asset that fails again and again, or takes a large share of downtime and maintenance cost. Finding the bad actors is usually the quickest way to cut downtime.
- CAPA (corrective and preventive action)
- A structured way to fix the cause of a problem (corrective action) and stop similar problems happening elsewhere (preventive action). A good CAPA has an owner, a due date, a verifier who is not the owner, and a check that the action actually worked.
- Calibration
- A documented comparison of an instrument's reading against a reference standard of known accuracy, with the tolerance, the result, a certificate and the next due date. Calibration records are core evidence in audited industries. See calibration traceability and what to keep from a NABL certificate.
- Casting yield
- Used in two ways. Metal yield is the weight of finished castings divided by the weight of metal poured, including gates and risers. Process yield is the number of good castings divided by the number poured. Always say which one you mean.
Process yield = Good castings / Castings poured - CCP (critical control point)
- A step in a food process where a control is essential to prevent, remove or reduce a food safety hazard to an acceptable level. CCPs are monitored against critical limits, and an overdue or failed check should stop the line from restarting.
- CMMS (computerized maintenance management system)
- Software that keeps maintenance work orders, preventive maintenance schedules, asset records, spare parts and maintenance history in one place, so a team can plan, do and prove the work instead of relying on spreadsheets and paper. The full guide is what is CMMS.
- Condition-based maintenance (CBM)
- Maintenance that is triggered when a measured condition, such as vibration, temperature or pressure, crosses a defined limit, rather than on a fixed calendar. It sits between time-based preventive maintenance and predictive maintenance.
- Condition monitoring
- Tracking measured asset parameters, such as temperature, vibration or pressure, against warning and critical limits. Readings can come from manual rounds or from PLC, SCADA and IoT systems. Condition monitoring is the data that condition-based and predictive maintenance run on. See condition monitoring without replacing your PLCs.
- Deviation
- A recorded departure from a specification, tolerance or procedure, such as an out-of-tolerance reading, together with the corrective work that resolves it.
- Downtime
- Time an asset or line cannot produce. Planned downtime is scheduled for maintenance or changeover. Unplanned downtime comes from breakdowns. Recording downtime by asset, cause and shift is the base of reliability analytics.
- Drift-to-limit
- A projection of when a parameter that is trending toward its limit will reach it, if the current trend continues. It turns a slowly rising reading into a date your planner can act on.
Time to limit = (Limit - Current value) / Rate of change - EAM (enterprise asset management)
- The wider discipline and software category for managing physical assets over their whole life, from planning and purchase through operation and maintenance to disposal. A CMMS is the maintenance core of an EAM program.
- FMEA (failure mode and effects analysis)
- A method for listing how an asset or process can fail, the effect of each failure and its risk, so you can design targeted maintenance and inspections.
- HIRA (hazard identification and risk assessment)
- A structured way to find the hazards in a task or area, rate the risk of each, usually from likelihood and severity, and decide on controls using the hierarchy of controls: elimination, substitution, engineering controls, administrative controls and PPE. The full guide is HIRA, done properly.
Risk score = Likelihood x Severity (on the scales your procedure defines) - Inherent availability
- The availability you would get if the only downtime were repair time for failures. It ignores waiting for parts, planned maintenance and other delays, so it is an upper bound.
Inherent availability = MTBF / (MTBF + MTTR) - LOTO (lockout tagout)
- A procedure that isolates machines from their energy sources and keeps them isolated during service and maintenance, using locks and tags so equipment cannot be restarted while someone is working on it. In the US, OSHA 29 CFR 1910.147 sets the requirements for the control of hazardous energy. The full guide is the lockout tagout procedure.
- Lot traceability
- The ability to follow a lot in both directions: back from a finished product to every material lot and process step that made it, and forward from a material lot to every product and customer it reached.
- LTIFR (lost time injury frequency rate)
- The number of lost time injuries per million hours worked. A lost time injury is one that keeps a person off work beyond the day of the injury, but definitions vary, so state yours. Some organizations use 200,000 hours as the base instead of 1,000,000. Work it out in the LTIFR and TRIR calculator.
LTIFR = Lost time injuries x 1,000,000 / Hours worked - Mass balance
- A check that the quantity of a material lot used equals the quantity accounted for in finished products, waste and remaining stock. Auditors use it to test whether a traceability system is complete.
- Mock recall
- A practice recall that tests whether traceability works under pressure. A good drill measures how long the trace takes and what share of the affected product was accounted for.
- MRO (maintenance, repair and operations)
- The spare parts, consumables and supplies used to keep equipment running. Managing MRO stock balances the risk of a stockout against the cost of holding stock. See how to set a reorder point.
- MTBF (mean time between failures)
- The average operating time between failures of a repairable asset. A higher MTBF means a more reliable asset. The counting rules are in MTBF vs MTTR, and the arithmetic is in the MTBF and MTTR calculator.
MTBF = Operating time / Number of failures - MTTF (mean time to failure)
- The average operating time until failure for parts that are replaced rather than repaired. It is used to plan replacements.
MTTF = Total operating time / Number of units failed - MTTR (mean time to repair)
- The average time to restore a failed asset to working order, including diagnosis, repair and testing. A lower MTTR means faster recovery. Read it next to MTBF in MTBF vs MTTR.
MTTR = Total repair time / Number of repairs - OEE (overall equipment effectiveness)
- A measure of how much of the planned production time is truly productive. It multiplies three factors: availability, performance and quality. Maintenance affects availability most directly. The formula and a worked example are on the OEE calculator. How to use the losses is in OEE for maintenance leaders.
OEE = Availability x Performance x Quality - Performance (OEE)
- How fast a machine ran while it was running, compared with its ideal speed. Small stops and slow cycles pull it down.
Performance = (Ideal cycle time x Total count) / Run time - Permit to work
- A formal written system that controls high-risk work, such as hot work, confined space entry or work on live systems. A permit states the work, the hazards, the controls and isolations, the people involved and the time it is valid, and the work is handed back formally when done. The full guide is how a permit to work system keeps hazardous jobs under control.
- Planned vs reactive work
- The split between maintenance scheduled in advance and unplanned breakdown work. Planned work is usually safer, cheaper and faster, so plants track the ratio over time.
- PM compliance
- The share of scheduled preventive maintenance done on time, within its allowed window. It is a leading indicator of reliability.
PM compliance = PMs completed on time / PMs scheduled - Predictive maintenance (PdM)
- Maintenance timed by evidence that a failure is becoming likely, such as a trend in vibration, temperature or oil analysis, so work happens before the failure rather than on a fixed interval.
- Preventive maintenance (PM)
- Maintenance done on a plan, by calendar date, running hours, meter reading or cycle count, to reduce the chance of failure. Start with the preventive maintenance guide, then the machine checklists for a compressor, CNC, hydraulic press, pump or EOT crane.
- Quality (OEE)
- The share of units made that were good the first time, without rework or scrap.
Quality = Good count / Total count - RCM (reliability-centered maintenance)
- A structured method for choosing the right maintenance strategy for each asset from its failure modes and their consequences, balancing run to failure, preventive and predictive approaches.
- Single sign-on (SSO)
- A login where people enter an application with the company identity IT already runs. In MaintenanceIQ, single sign-on still leaves role, factory and department permissions in charge of what each person can see.
- TPM (total productive maintenance)
- An approach that makes equipment care everyone's job, not only the maintenance team's. Operators take on routine care such as cleaning, inspection and lubrication, and the plant works systematically to remove losses. OEE is its usual headline measure. The full guide is total productive maintenance.
- TRIR (total recordable incident rate)
- The number of recordable work-related injuries and illnesses per 200,000 hours worked. OSHA uses 200,000 hours as the base because it equals 100 full-time employees working 40 hours a week for 50 weeks. Work it out in the LTIFR and TRIR calculator.
TRIR = Recordable cases x 200,000 / Hours worked - Work order
- The record of one maintenance job: what to do, on which asset, by whom, with which parts, and the proof that it was done.
- Wrench time
- The share of a technician's paid time spent actually doing maintenance, as opposed to walking, waiting for parts or looking for information.