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LEV testing - ductwork
A leak in LEV ductwork does not announce itself, but it steals the airflow the system depends on - so a hood a long way from the leak quietly stops capturing. Small holes, big consequences for control.
The short answer
Leaks in LEV ductwork - at joints, damaged sections, or badly-sealed access - let air into the system where it should not, robbing the hoods of the airflow they need to capture contaminant at source. Because the fan can only move so much air, a leak in one place reduces capture at the hoods, often ones far from the leak. So a leaking system quietly under-performs and can fail to control exposure, which is exactly the kind of degradation LEV testing is designed to find.
How LEV depends on the ductwork
An LEV system works by the fan pulling air through the ductwork to create the capture airflow at each hood - the airflow that draws contaminant in at source. That airflow is a shared, finite resource: the fan can only move so much air, and it has to be distributed across all the hoods and the runs that serve them. The system is balanced to deliver the right capture at each point from that shared airflow.
This is why the integrity of the ductwork matters so much. The capture at the hoods depends on the air travelling all the way from the fan through sealed ductwork to the point of capture. Anything that lets air into the system along the way - a leak - diverts some of that finite airflow away from where it is needed, undermining the balance the system relies on.
What a leak does
A leak is a hole where air enters the ductwork uninvited - a failed joint, a split or corroded section, a badly-sealed or missing access panel. Because the fan is pulling a fixed amount of air, air drawn in through a leak is air not drawn in through the hoods. The leak effectively competes with the hoods for the fan's finite capacity, and the hoods lose some of the airflow they need to capture properly.
The counter-intuitive part is that the effect shows up away from the leak. A leak on one branch can rob airflow from hoods elsewhere in the system, so a hood that is perfectly intact can under-perform because of a leak somewhere the operator would never connect it to. The symptom - a hood not capturing - and the cause - a leak far away - can be in completely different places.
Why it is dangerous
The danger of ductwork leaks is that they degrade the control invisibly. The system still runs, the fan still turns, and the leak makes no obvious sign - but the hoods it has robbed are capturing less than they should, letting contaminant escape into the breathing zone of the people working at them. The exposure the LEV is meant to prevent starts happening again, quietly, because of a hole the operator cannot see and would not think to look for.
Leaks also tend to worsen over time - joints work loose, corrosion spreads, access seals perish - so a system's capture can drift downward gradually as leaks accumulate, without any single dramatic failure. That slow, hidden degradation is exactly the kind that leaves a system controlling exposure far less well than everyone assumes, until something reveals it.
Why testing finds it
This is one of the clearest cases for measured LEV testing rather than trusting appearances. A thorough examination and test measures the actual capture and airflow at each hood, so a hood under-performing because of a leak elsewhere shows up in the readings - the measured shortfall reveals that the system is not delivering what it should, even though nothing looks wrong. The test catches the effect of the leak where a glance never would.
A good examination also looks at the condition and integrity of the ductwork itself, so leaks can be identified as the cause of measured under-performance and put right. Sealing the leaks restores the airflow to the hoods and the capture they provide - so testing not only detects the problem but points to the fix, which is exactly what turns a hidden degradation into something you can correct.
The takeaway
Ductwork leaks are a quiet but real threat to LEV performance: they steal the finite airflow the system relies on, cause hoods to under-capture in ways that show up far from the leak, and degrade control invisibly as they worsen. A system with leaks is a system controlling exposure less well than it appears to, often without anyone realising.
The defences are integrity and measurement - keeping the ductwork sealed and sound through maintenance, and testing the system's actual performance so that any leak-induced shortfall is caught and traced. A properly tested system reveals what a leaking one hides: whether the hoods are really capturing. Sealed ductwork keeps the airflow where it belongs, and measured testing confirms it is getting there.
Questions
They let air into the system where it should not enter, robbing the hoods of the finite airflow they need to capture contaminant at source. So hoods under-perform - often ones far from the leak - and the system controls exposure less well than it appears to.
Because the fan moves a fixed amount of air shared across the system. Air drawn in through a leak is air not drawn in through the hoods, so a leak on one branch can rob airflow from hoods elsewhere - the symptom and the cause can be in different places.
They degrade control invisibly. The system still runs and the leak makes no obvious sign, but the robbed hoods capture less than they should, letting contaminant escape into the breathing zone - and leaks tend to worsen over time, drifting capture downward.
At failed joints, split or corroded sections of ductwork, and badly-sealed or missing access panels - anywhere a hole lets air into the system uninvited to compete with the hoods for the fan's capacity.
A thorough examination measures actual capture and airflow at each hood, so a hood under-performing because of a leak shows up in the readings even though nothing looks wrong. Examining the ductwork's integrity then identifies the leak as the cause.
Sealing the leaks - restoring the ductwork's integrity through maintenance - which returns the airflow to the hoods and the capture they provide. Testing detects the shortfall and points to the fix.
We measure capture at each hood and examine ductwork integrity, so a leak degrading your LEV shows up in the readings and can be put right.
