ISO 20816-1:2016 superseded ISO 10816-1, and ISO 20816-3 carries forward the industrial-machine severity framework while adding shaft-vibration guidance absorbed from ISO 7919 [S1][S2][S5].
Both frameworks classify broadband RMS vibration velocity into Zones A, B, C and D, but the applicable numeric boundary depends on machine group, power, shaft height, support stiffness and measurement arrangement [S2][S3][S4].
What Changed Between ISO 10816 and ISO 20816
ISO 10816-1 was replaced by ISO 20816-1:2016, and the widely used industrial-machine requirements formerly in ISO 10816-3 were carried into ISO 20816-3 [S2][S5][S6]. The four evaluation zones did not change: Zone A describes the as-new condition, Zone B is acceptable for unrestricted long-term operation, Zone C is unsatisfactory for continuous operation and permits only limited operation pending corrective action, and Zone D is severe enough to cause damage [S2][S4].
The transition is not merely a change of document number. ISO 20816-3 covers industrial machines above 15 kW operating between 120 and 30,000 r/min and provides guidance for measurements on rotating and non-rotating parts under normal operating conditions [S3]. It also absorbed the shaft-vibration criteria of ISO 7919-3, so new reports can cite ISO 20816-3 rather than retaining the legacy ISO 10816-3 reference [S2][S5].
ISO 20816-1 permits different measurement quantities and methods when they are well-defined and their limitations are stated [S1]. That flexibility is not permission to mix readings from incompatible methods. Specify the measurement quantity, frequency band, sensor location, machine category and support class in every assessment procedure.
Select the Correct Machine Group and Support Class
ISO 20816-3 divides general industrial machinery by power and shaft centre height: Group 1 includes machines above 300 kW and electrical machines with shaft height H ≥ 315 mm, while Group 2 includes machines from 15 to 300 kW and electrical machines with 160 mm ≤ H < 315 mm [S2]. Flexible couplings, rigid couplings, separate drivers and integrated pump arrangements require classification against the applicable machine definition rather than a blanket size rule [S3][S4].
Because stiffness can differ by direction, the same machine can be classified as rigid horizontally and flexible vertically.
Flexible supports generally receive different boundary values from rigid supports [S2].
Compare the Main Evaluation Methods
ISO 10816 and ISO 20816 use the same broad severity concept: broadband RMS velocity on a non-rotating part, normally a bearing housing, over 10–1,000 Hz [S2][S5]. ISO 20816-3 extends the evaluation framework to industrial installations above 15 kW and 120–30,000 r/min, including turbines, compressors, motors, rollers, mills, transporters, couplings, blowers and fans [S3].
ISO 20816-3 provides guidelines for applying vibration-evaluation criteria to measurements made on both rotating and non-rotating parts of coupled industrial machines under normal operating conditions [S3]. ISO 20816-3 applies to coupled industrial machines with power greater than 15 kW and operating speeds between 120 and 30,000 r/min when measurements are performed on site [S3].
ISO 20816-1 permits alternative measurement quantities and methods only when their definitions and limitations are documented [S1]. In practical terms, ISO 20816-3 offers the broader industrial-machine framework, while a legacy ISO 10816 procedure remains useful only when its machine classification and measurement method remain valid for the asset and contract.
Measurements and Readings That Can Be Misapplied
The usual evaluation quantity is broadband RMS vibration velocity in millimetres per second over a standard frequency band, typically 10 to 1,000 Hz [S5].
Broadband velocity identifies severity, not fault cause; unbalance, misalignment and looseness usually require a spectrum, phase analysis and other diagnostic evidence [S5].
Sensor mounting, resonance, operating state and measurement repeatability can alter the result. ISO 20816-3 evaluates steady-state values and the variation permitted around them under normal operating conditions [S3]. Do not apply a numeric zone directly to a transient start-up or shutdown trace, and do not treat a single broadband reading as a diagnosis when the machine-specific limits are unavailable.
Apply the Zones to Operating Decisions
Zone A is the baseline for newly commissioned machinery, Zone B is suitable for unrestricted long-term operation, Zone C requires a time-bounded response, and Zone D is a damage-risk condition requiring immediate investigation [S2][S4]. Zone C should therefore generate a corrective-action plan with an operating deadline, not an indefinite watch condition or an automatic shutdown instruction [S4].
For example, 3.2 mm/s RMS can fall into different zones depending on machine group and support class, so a number quoted without those two dimensions is incomplete [S4]. This is the central engineering reason not to transplant a generic 4.5 mm/s threshold from one machine to another [S5]. The vibration alarm thresholds reference is useful when translating severity zones into plant alarm logic.
ISO 20816-3 also limits the universal use of fan criteria. Its vibration criteria generally apply to fans above 300 kW or fans that are not flexibly supported; other fan arrangements require an agreed evaluation using manufacturer requirements and operating experience [S3]. Similar machine-specific checks are essential for lightweight equipment and coupled systems.
Separate Standards Use from Equipment Acceptance
ISO 20816 severity limits are reference values based on international experience and must be applied with knowledge of each machine’s characteristics because the values may not be fully adequate for every installation [S3]. Manufacturer acceptance criteria, contractual guarantees, site-specific baselines and OEM alarm settings can be stricter and should remain traceable in the maintenance record.
For pumps, define data collection by failure risk and consequence, not by selecting one universal velocity number, as described in Set Critical Pump Vibration Collection by Failure Risk. ISO 20816-3 can provide the severity framework, but the protected system, criticality, operating speed and support classification determine which measurements and actions matter.
The source standard remains the controlling document for numerical boundaries. Secondary charts, calculators and legacy ISO 10816 tables are aids for locating a likely zone, not substitutes for verifying the applicable edition, machine scope, support class and measurement conditions [S2][S4][S6].
Build a Defensible Assessment Procedure
For each monitored machine, record the applicable ISO 20816 part, machine group, rated power, speed range, shaft height, coupling arrangement, support classification and measurement points. Record broadband RMS velocity in mm/s, frequency band, operating condition, sensor path and direction, then apply the zone boundary for that exact machine cell [S1][S3][S4].
Trend Zone A and B readings for deterioration from baseline, schedule corrective action for Zone C, and apply the site’s emergency decision process to Zone D [S2]. Where shaft-relative measurements, specific frequency components or machine-specific acceptance tests are required, add those data rather than forcing every question into a housing-vibration zone [S3].
Track two implementation signals for every critical asset: the percentage of machines with confirmed group and support classification, and the time between entry into Zone C and completed corrective action. Both expose whether the severity scheme is being used as an engineering control or merely copied into an alarm database.