ISO 10816 is the standard most handheld vibration instruments and route-based reports reference when they attach a severity to a reading. Understanding the zones it defines turns an unexplained '7.1 mm/s' into a decision about whether to act now, plan it, or keep watching. This guide explains the four severity zones and gives you a simplified chart for triaging your own measurements on medium-sized machines.
What ISO 10816 actually measures
ISO 10816 rates machine condition using broadband vibration velocity, measured in millimetres per second RMS, typically over a 10 to 1000 Hz frequency range. Velocity is chosen deliberately: it correlates well with fatigue and wear across the middle of the frequency spectrum, where most bearing and gear faults live.
The standard divides machines into classes by size, power and mounting — for example, medium machines on flexible foundations (Class II) versus large machines on rigid foundations (Class III). Each class has its own zone boundaries, so the same 5 mm/s reading can mean different things on different assets. For handheld route work on most SME plant, Class II and Class III cover the bulk of motors, pumps and fans.
The four severity zones, in plain English
Every ISO 10816 reading falls into one of four zones. They are not pass/fail limits so much as a triage system that tells you how urgent a finding is and what to do next.
- Zone A — Acceptable. A new or recently overhauled machine in good condition. No action; keep it on the route.
- Zone B — Satisfactory. Safe for long-term, continuous operation. Note it, watch the trend, and keep monitoring.
- Zone C — Unsatisfactory. Not suitable for long-term continuous operation. Plan corrective action at the next available opportunity.
- Zone D — Unacceptable. Vibration is severe enough to damage the machine. Stop or reduce load and act immediately.
A simplified severity chart for handheld readings
The figures below are indicative boundaries for Class II and Class III machines — the common territory for SME motors, pumps and fans. Always confirm against the specific standard part and your machine's class before acting on a single reading, and treat the trend as more reliable than any one snapshot.
- 0 – 1.4 mm/s RMS — Zone A. Healthy. New-machine territory.
- 1.4 – 2.8 mm/s RMS — Zone B. Satisfactory. Normal operation, keep trending.
- 2.8 – 4.5 mm/s RMS — Zone C. Unsatisfactory. Plan corrective work, investigate the fault type in the spectrum.
- Above 4.5 mm/s RMS — Zone D. Unacceptable. Act now; restrict operation and raise a work order.
Using the chart without falling into its traps
Three cautions make the difference between a useful triage tool and a misleading one. First, ISO 10816 thresholds assume steady-state operation at normal load and speed — a machine ramping up or running unloaded will give a reading you cannot compare against the chart.
Second, overall velocity misses some faults entirely. Early-stage bearing defects and lubrication problems often live in the high-frequency spectrum, above the 1000 Hz window the standard measures. A machine can be failing while its overall velocity sits comfortably in Zone A — which is exactly why trend analysis and spectrum review still matter alongside any severity band.
Third, consistency beats precision. The same point, the same orientation, the same load, every month. A steady climb through the zones is a far stronger signal than any single reading against a threshold.
How this fits a monthly route
ISO 10816 gives you the triage layer; the spectrum gives you the diagnosis. Together they turn a handheld route into a repeatable, comparable programme: the severity band tells you when to act, and the frequency analysis tells you what is wrong and whether a planned shutdown will catch it.
That combination is exactly what a prioritised monthly report should deliver — a zone, a diagnosis, a recommended action and a timescale, rather than a bare number and a guess.