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LEV testing - when it fails
A failed LEV test sounds alarming, but it is actually the system doing its job - catching a problem before it became a worker's illness. Understanding what a failure means, why systems fail, and what happens next turns a worrying result into a clear course of action.
The short answer
A failed LEV test means the system is not adequately capturing the contaminant and controlling exposure - the readings or observations show it is not doing its job. Systems fail for identifiable reasons: lost capture at the hood, blocked or leaking ductwork, a worn or tired fan, clogged filters, or an inadequate design. A failed test is the examination catching that before it became a worker's illness. What happens next is diagnosis and repair - fixing the cause and re-testing to confirm the system controls exposure again.
What a failure means
A failed LEV test can sound like bad news, but the first thing to understand is simply what it means: the system is not adequately capturing the contaminant and controlling exposure. The test - measuring airflow and capture, and observing whether the contaminant is drawn in - has found that the system is not performing to the level needed to control the hazard. So a failure is a finding that the LEV, at the time of the test, is not doing its fundamental job of protecting workers from the contaminant it is there to control.
Framed that way, a failed test is actually the system of protection working. LEV is tested precisely to catch when it is not controlling exposure, so a failure is the test succeeding at its purpose - identifying a system that has fallen short before that shortfall became a worker breathing more of the hazard than they should. A failure is a warning caught in time, not a disaster. It tells you the LEV needs attention now, which is far better than the alternative of the same shortfall going undetected and causing harm. So a failure, while it demands action, is the process doing its job.
Why systems fail
LEV systems fail for a set of identifiable, recurring reasons, which is useful because it means a failure can usually be diagnosed. Lost capture at the hood is common - the hood no longer draws the contaminant in effectively, perhaps because it is damaged, poorly positioned, or the airflow to it has dropped. Blocked or partially-blocked ductwork restricts the airflow, as dust or debris accumulates inside; leaks in the ductwork lose airflow before it reaches the hood. Each of these reduces the capture the system achieves.
The fan and filters are frequent culprits too. A worn or tired fan moves less air than it should, so the whole system draws less; clogged filters restrict airflow as they load up. And sometimes the failure is one of design - a system that was never adequate for the task, or was changed (a point added) so it no longer delivers the airflow needed. So a failure usually traces to one or more of these: lost capture, blocked or leaking ducts, a weak fan, clogged filters, or inadequate design. Knowing the common causes is what turns a failure from a mystery into a diagnosis.
How the test reveals it
A failure shows up in the test through the measurements and observations that make up a proper examination. On the measurement side, the airflow and capture velocities come back below what the system needs to achieve for the contaminant - the numbers show the system is not moving or capturing enough air. A reading below the required level at a hood, or a duct velocity that is too low, is a measured indication that the system is not performing. The quantitative side of the test puts a number on the shortfall.
On the observation side, the qualitative checks - using smoke or a dust lamp to see whether the contaminant is actually captured - can show the contaminant escaping the hood rather than being drawn in, which is a direct sign of failure regardless of the numbers. So a failure can be revealed by the measurements falling short, by observation showing the contaminant not captured, or both. This is why a proper test uses both approaches - together they reveal the shortfall clearly, whether it shows in the numbers, the observed capture, or a combination. The failure is the test finding, by measurement and observation, that the system is not controlling exposure.
What happens next
The important part of a failed test is what happens next, and it follows a clear path: diagnose the cause, repair it, and re-test to confirm the system controls exposure again. The test that found the failure usually also indicates where the problem lies - which hood, which part of the system is underperforming - so the diagnosis has a starting point. From there, the specific cause is identified: the blocked duct, the worn fan, the clogged filter, the poorly positioned hood, or the design inadequacy, whatever it turns out to be.
Then the cause is repaired - clearing the blockage, fixing the leak, replacing or servicing the fan, changing the filters, correcting the hood, or upgrading the system where the design fell short. And crucially, after the repair the system is re-tested, to confirm the fix has actually restored the capture and the system now controls exposure. The re-test is what closes the loop, verifying the system is back to doing its job. So a failed test is the start of a process - diagnose, repair, re-test - that ends with a system confirmed to be controlling exposure again, which is exactly what the failure was flagging the need for.
The takeaway
A failed LEV test means the system is not adequately capturing the contaminant and controlling exposure - the measurements or observations show it is not doing its job. Systems fail for identifiable reasons: lost capture at the hood, blocked or leaking ductwork, a worn fan, clogged filters, or an inadequate design. The test reveals the failure through readings below the required level, observation of the contaminant escaping, or both.
But a failed test is the system of protection working, not a disaster - it is the examination catching a shortfall before it became a worker's illness. And it leads to a clear course of action: diagnose the cause, repair it, and re-test to confirm the system controls exposure again. So a failure, while it demands prompt action, is a problem caught in time - the test doing exactly what it exists to do, and the start of putting the system right rather than the end of anything. Understanding its anatomy turns an alarming result into a clear path forward.
Questions
That the system is not adequately capturing the contaminant and controlling exposure - the measurements or observations show it is not performing to the level needed to protect workers from the hazard it is there to control.
No - it is the system of protection working. LEV is tested precisely to catch when it is not controlling exposure, so a failure is the test succeeding at its purpose: identifying a shortfall before it became a worker breathing more of the hazard than they should. It is a warning caught in time.
For identifiable reasons - lost capture at the hood (damaged, poorly positioned, or low airflow), blocked or leaking ductwork, a worn or tired fan moving less air, clogged filters restricting airflow, or an inadequate or changed design that no longer delivers the airflow needed.
Through measurements (airflow and capture velocities coming back below what the system needs) and observations (smoke or dust-lamp checks showing the contaminant escaping the hood rather than being captured). A failure can show in the numbers, the observed capture, or both.
Diagnosis, repair and re-test. The test usually indicates where the problem lies; the specific cause is identified and repaired - clearing a blockage, fixing a leak, servicing the fan, changing filters, correcting a hood; then the system is re-tested to confirm it controls exposure again.
Because the fix has to be confirmed to have actually restored the capture. The re-test closes the loop, verifying the system is back to controlling exposure - which is exactly what the failure flagged the need for. Without it, you have a repair but no confirmation it worked.
We test LEV thoroughly, diagnose the cause of any failure, and re-test after repair - so a failure becomes a problem caught in time and a system confirmed to control exposure again.
