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LEV testing - system changes
It seems harmless: your workshop grows, you add a bench, and you connect it to the existing extraction. But an LEV system is designed to capture from a specific number of points, and quietly adding another can rob the whole system of the airflow it needs - leaving every point, old and new, controlling exposure less well than before.
The short answer
An LEV system is designed to move a specific volume of air and capture from a specific number of points. Adding a workstation or extraction point to it - without redesigning the system and re-testing - shares the same finite airflow across more points, so each point, including the existing ones, can end up drawing less than it needs to control exposure. What looks like a simple extension can leave the whole system under-performing and no longer controlling the hazard it was verified to control - which is why any change needs the system reassessed and re-tested.
LEV is designed as a whole
The key thing to understand is that an LEV system is designed as a whole to do a specific job: capture a contaminant at a specific number of points, using a fan and ductwork sized to move the airflow those points need. The system is balanced - the fan's capacity, the ductwork, and the capture at each point are all designed together so that every point gets the airflow required to control the exposure there. It is not a general-purpose extraction you can tap into anywhere; it is a designed system with a designed capacity, matched to the points it was built for.
This matters because the system's airflow is finite - the fan moves only so much air, and that capacity is divided among the points connected to it. When the system was designed and verified, that finite airflow was matched to the number of points, so each got enough. The whole thing works because the demand (the points) and the supply (the fan's airflow) were balanced in the design. Anything that changes that balance - like adding a point - changes whether each point still gets what it needs, which is exactly the risk in extending a system without reassessing it.
Adding a point shares the airflow
When you add a workstation or extraction point to an existing LEV system, you are adding demand without adding supply - more points drawing on the same fan and its same finite airflow. The result is that the airflow is now shared among more points than the system was designed for, so each point, on average, gets less. The fan cannot magically move more air because you connected another branch; it moves what it moves, now divided further. So the new point may draw poorly, and, crucially, the existing points may draw less than before too, because the total airflow they used to share among themselves is now shared with the addition.
This is the counter-intuitive part: adding a point does not just risk the new point being inadequate - it can weaken the points that were working fine. The system was balanced for its original points; adding another unbalances it, pulling airflow away from the existing points to feed the new one, so all of them can end up under-performing. A change that seems to only affect the new bench can quietly degrade the capture across the whole system, because the finite airflow now has more places to go and less to give each of them.
Why it's a real risk
The reason this is a genuine risk, not just an inefficiency, is what LEV is for: controlling exposure to a hazardous contaminant. If adding a point drops the airflow at the points below what they need to capture the contaminant effectively, then the system is no longer controlling exposure as it was verified to - workers at those points are breathing more of the hazard than the system was supposed to allow. And because the drop can affect all the points, the exposure risk can spread across the whole workshop, not just the new bench, silently.
It is silent because nothing obvious announces it. The system still runs, the extraction still appears to work, and there is no visible sign that the airflow has dropped below what each point needs. So the addition can leave the whole system quietly failing to control exposure, with no one aware that the capture has degraded. This is exactly the kind of hidden loss of control that makes LEV dangerous when changed carelessly - the system looks the same, but it is no longer doing the job it was verified to do, because its balance was disturbed by an addition it was never designed for.
What to do instead
The right way to add a workstation or extraction point is to treat it as a change to the system that requires reassessment, not a simple connection. Adding a point means the system needs to be reassessed - can the fan and ductwork actually handle the additional point while still delivering the required airflow to every point, or does the system need upgrading (a larger fan, modified ductwork) to cope? A competent assessment determines whether the existing system can take the addition or whether it has to be redesigned to maintain proper capture at all points.
And after any such change, the system needs to be re-tested, because the thorough examination and test that verified it was for the system as it was - a different system, with a different point, needs re-verifying to confirm it still controls exposure at every point. So the rule is: do not quietly add a point and assume it is fine; reassess whether the system can take it, upgrade if needed, and re-test to confirm the whole system still works. That is how a change is made without leaving the system under-performing - by ensuring the airflow still meets the demand at every point, and proving it does.
The takeaway
An LEV system is designed as a balanced whole - a fan and ductwork sized to deliver the airflow a specific number of points need. Adding a workstation or extraction point without redesigning and re-testing shares the same finite airflow among more points, so each point, including the existing ones, can end up drawing less than it needs. What looks like a simple extension can leave the whole system under-performing and no longer controlling the hazard it was verified to control - silently, with no obvious sign.
So a change to an LEV system is never as simple as connecting another branch. Any addition unbalances the system, and the right response is to reassess whether the fan and ductwork can handle it while still delivering the required airflow everywhere, upgrade the system if they cannot, and re-test to confirm it still controls exposure at every point. Do not tell your LEV about a new workstation only by bolting one on - reassess and re-test the change, so the system keeps doing the job it was designed and verified for.
Questions
Because an LEV system is designed to move a finite volume of air and capture from a specific number of points. Adding a point shares that same airflow among more points, so each - including the existing ones - can end up drawing less than it needs to control exposure.
The fan moves a finite amount of air, divided among the connected points. Adding a point pulls airflow away from the existing points to feed the new one, so the system - balanced for its original points - is unbalanced, and all the points can end up under-performing.
Because LEV controls exposure to a hazardous contaminant. If the airflow at the points drops below what they need to capture it, the system no longer controls exposure as verified - workers breathe more of the hazard - and the drop can affect the whole workshop, not just the new bench.
Because nothing obvious announces it - the system still runs and appears to work, with no visible sign the airflow has dropped. So the addition can leave the whole system quietly failing to control exposure, with no one aware the capture has degraded.
Treat it as a change requiring reassessment, not a simple connection. Have the system reassessed to see if the fan and ductwork can handle the extra point while still delivering the required airflow everywhere - upgrading if needed - and re-test to confirm it still works.
Yes. The thorough examination and test that verified the system was for the system as it was. A different system, with an added point, needs re-verifying to confirm it still controls exposure at every point - the previous test no longer covers the changed system.
We reassess and re-test LEV after changes - confirming the system can still deliver the airflow every point needs when a workstation is added, so a simple extension never weakens the whole system.
