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LEV testing - silent failure
A broken extraction system gets fixed, because everyone can see it is broken. The dangerous one is the system that still hums, still pulls a little air, and has quietly stopped protecting anyone - looking fine the whole time.
The short answer
The most dangerous LEV failure is the silent one: a system that still runs, still moves some air, and still looks and sounds normal, but has quietly degraded to the point where it is no longer controlling exposure. Because nothing about it appears wrong, nobody investigates, and the exposure it should be preventing carries on unseen. Only measured testing - not appearances - can catch a system that has failed quietly while looking fine.
The illusion of a running system
There is a natural assumption that if an extraction system is running - the fan turning, air moving, the usual hum - then it is doing its job. That assumption is exactly what makes silent failure so dangerous, because a system can run perfectly and still not control exposure. Running is a sign the fan has power; it is not a sign the hoods are capturing what they should. The two are easily confused, and the confusion is where the risk hides.
So a system that looks fine tells you very little about whether it is working. The visible, audible signs of an LEV system - the fan running, some air being drawn - are present whether the system is capturing exposure adequately or has degraded well below what is needed. Appearances confirm the system is on, not that it is protecting anyone, and mistaking one for the other is how a failing system passes unnoticed.
How it fails without a sign
LEV rarely fails dramatically. It drifts: filters gradually load and restrict airflow, ductwork develops slow leaks, a fan quietly loses efficiency, a hood gets nudged out of position, or a workstation is added that robs airflow from the rest. Each change is small and invisible on its own, and none of them stops the system running - so day to day nothing looks different, while the cumulative effect pulls the system below adequate control.
That gradualness is what hides the failure. There is no moment when the system visibly breaks, just a slow slide over months during which capture quietly declines. Because no single day looks different from the last, nobody notices the system crossing from working to failing - and by the time anything reveals it, the system may have been under-protecting people for a long time, all while looking exactly as it always did.
Why quiet failure is the worst kind
A silently-failing system is more dangerous than an obviously broken one, precisely because it looks fine. A broken system gets reported and fixed - everyone can see it is not working. A quietly-failing one is left exactly because it appears normal, so the exposure it is no longer controlling continues, day after day, with everyone assuming they are protected. The appearance of working is what removes the pressure to investigate.
And the harm it allows is itself invisible and slow, as with all occupational exposure - so there is no feedback loop to reveal the problem either. A failing but normal-looking system, exposing people to a hazard that harms them slowly and without symptoms, can run for a very long time with no one aware. Quiet failure combines the worst of both: a control that has stopped working and a harm that gives no warning, hidden behind a system that looks fine.
Why only testing catches it
Because appearances cannot reveal silent failure, the only reliable way to catch it is measurement - a thorough examination and test that takes real readings of capture and airflow at each point and compares them against what the system should achieve. A system that looks fine but has degraded shows the truth in its measured performance: the readings reveal the shortfall that the eye and ear cannot. Testing is what converts a hopeful assumption into a known fact.
This is the whole reason LEV testing exists on a regular cycle rather than relying on people noticing problems. Silent, gradual failure is precisely what a periodic measured test is designed to catch - a scheduled check that looks past the reassuring appearance and measures whether the system is actually still controlling exposure. Without it, a quietly-failing system has nothing to reveal it until harm does.
The takeaway
The lesson of the LEV that looked fine and failed quietly is not to trust appearances with extraction. A running, normal-looking system may be controlling exposure perfectly or may have degraded well below adequate - and there is no way to tell by looking, listening, or assuming. The only way to know is to measure, which is exactly what testing does.
So the reassurance of a system that seems fine is worth very little on its own; the reassurance that matters is a current, measured test confirming it is genuinely controlling exposure. Treating LEV as fine because it looks fine is how silent failures are left to run. Testing it, on the cycle, is how they are caught - before the quietly-failing system that looked fine has been harming people all along.
Questions
One that still runs, still moves some air, and looks and sounds normal, but has quietly degraded to where it no longer controls exposure. Because nothing appears wrong, nobody investigates, and the exposure carries on unseen.
Because running only shows the fan has power - not that the hoods are capturing what they should. A system can run perfectly and still have degraded well below adequate control. Appearances confirm it is on, not that it is protecting anyone.
Gradually - filters load, ductwork leaks, a fan tires, a hood is nudged, a workstation robs airflow. Each change is small and invisible and none stops the system running, so it slides from working to failing over months with no visible moment of failure.
Because a broken system gets reported and fixed, while a quietly-failing one is left precisely because it looks fine - so the exposure continues with everyone assuming they are protected. The harm it allows is invisible and slow too, so nothing reveals it.
Only by measurement - a thorough examination that takes real readings of capture and airflow at each point and compares them against what the system should achieve. The readings reveal a shortfall the eye and ear cannot.
Because silent, gradual failure is exactly what a periodic measured test is designed to catch - a scheduled check that looks past the reassuring appearance. Without it, a quietly-failing system has nothing to reveal it until harm does.
We measure your extraction's real performance - catching a system that has quietly failed while looking fine, which appearances never reveal.
