Home / LEV Testing / Guide
LEV testing - the design benchmark
There is no universal pass mark for LEV that every system must hit. Instead, your system is judged against what it was specifically designed to do - the performance it was built to achieve to control your particular hazard. Understanding why the original design is the benchmark explains a lot about how LEV testing works, and why that is the right yardstick rather than a one-size-fits-all figure.
The short answer
LEV is benchmarked against its original design because there is no single pass mark that fits every system - each is designed for a specific process and hazard, with the airflow and capture velocity that particular situation requires. The performance a system was designed to achieve, confirmed at commissioning, is the benchmark the test measures against: the question is whether the system is still achieving what it was built to achieve. This is the right yardstick because it ties the test to what your system actually needs to do to control your hazard, rather than to a generic figure that could be too much for one system and nowhere near enough for another.
There is no universal pass mark
It would be simpler if there were a single number every LEV had to hit to pass - a universal pass mark. But there is not, and there cannot be, because LEV systems are not interchangeable. Each is designed for a specific process controlling a specific hazard, and different hazards need different degrees of control: the airflow and capture velocity required to control one contaminant may be quite different from what another needs. A system extracting a fine, hazardous dust may need to achieve much more than one handling a less demanding contaminant. So the performance that counts as adequate is specific to the system and its purpose, not a fixed figure.
This is why LEV testing does not work by comparing every system to one standard. Instead, each system is judged against what it was designed to do - the performance it was specifically built to achieve to control its particular hazard. That design intent is the benchmark. Understanding this clears up a common confusion: people sometimes expect a single pass mark and are puzzled that the test is about the specific system. The answer is that a specific system controlling a specific hazard has a specific requirement, and it is against that - its own design intent - that its performance is properly judged.
The design intent as benchmark
The original design of a system sets out what it was meant to achieve: the airflow, the capture velocity at each hood, the pressures - the performance figures that the designer determined would control the hazard in question. These design figures, confirmed when the system was commissioned and shown to be working correctly, are the benchmark for its later testing. The question each thorough examination asks is, in essence, whether the system is still achieving what it was designed and confirmed to achieve - whether the performance has held against the intended figures, or dropped away from them.
This makes the design intent, captured at commissioning, the reference point the whole testing regime turns on. A test measures the current performance and compares it against the design benchmark: performance at or above the intended figures indicates the system is still doing its job; performance that has fallen below indicates a decline that needs addressing. So the benchmark is not abstract - it is the concrete set of figures the system was built to deliver, recorded when it was proven to deliver them. Testing against it is asking whether the system today still matches the system that was confirmed to work, which is the meaningful comparison for judging whether it is still controlling exposure.
Why this is the right yardstick
Benchmarking against the original design is the right approach because it ties the test to what your system actually needs to do. The design intent embodies the specific requirement for controlling your particular hazard - it is, in effect, the answer to the question of how much control this situation needs, worked out for your process and contaminant. Judging the system against that means judging it against its real purpose: is it still delivering the control this hazard requires? That is exactly the question that matters, and the design benchmark is what makes the test able to answer it for your specific system.
A universal pass mark could not do this. A single figure applied to every system would be arbitrary relative to any particular one: too demanding for a system controlling an easy contaminant, so it would fail systems that are actually adequate, and nowhere near enough for a system controlling a dangerous one, so it would pass systems that are actually failing to protect people. Only a benchmark specific to the system - its own design intent - correctly reflects what that system needs to achieve. So testing against the original design is not just a convention; it is the only way to judge each system against its real requirement, which is why it is the right yardstick.
Why the design record matters
Because the original design is the benchmark, having a record of it matters a great deal - which is why commissioning data and the design specification are so important to keep. The design figures and the commissioning results are the benchmark the tests compare against; without them, a test has no proper reference. It can measure what the system is doing now, but it cannot as confidently say whether that represents the performance the system should achieve, because it does not know what the system was designed and confirmed to achieve. The benchmark is what turns a measurement into a judgement.
So the design benchmark and its record are foundational to meaningful testing. With them, each examination can compare the system against its own intended performance and judge whether it is holding up or declining. Without them, testing is harder and less certain - working out what the system ought to achieve after the fact, rather than comparing against a known, recorded intent. This is a strong reason to ensure the design and commissioning records are kept with the system's documentation: they are the yardstick every future test relies on. Benchmarking against the original design only works if the original design is recorded - which is why the design intent, once established, is worth preserving as the reference for the system's whole life.
The takeaway
There is no universal pass mark for LEV, because every system is designed for a specific process and hazard with its own requirement for control. Instead, a system is benchmarked against its original design - the airflow and capture velocity it was built to achieve, confirmed at commissioning. Each thorough examination asks whether the system is still achieving what it was designed and proven to achieve, comparing current performance against that design benchmark.
This is the right yardstick because it ties the test to what your system actually needs to do to control your hazard, rather than to a generic figure that would be too much for one system and nowhere near enough for another. And because the design intent is the benchmark, keeping the design and commissioning records matters - they are the reference every future test relies on. Your LEV is judged against its own purpose, worked out for your process and contaminant, which is the only comparison that correctly says whether it is still controlling exposure.
Questions
No, and there cannot be. Each system is designed for a specific process and hazard, and different hazards need different degrees of control - the airflow and capture velocity one contaminant needs may differ greatly from another. So the adequate performance is specific to the system and its purpose, not a fixed figure.
Its original design - the airflow, capture velocity and pressures it was specifically built to achieve to control your hazard, confirmed when it was commissioned and shown to work. Each examination asks whether the system is still achieving what it was designed and proven to achieve.
Because it embodies the specific requirement for controlling your particular hazard - the answer to how much control this situation needs, worked out for your process and contaminant. Judging the system against that means judging it against its real purpose, which is exactly the question that matters.
Because it would be arbitrary for any particular system - too demanding for one controlling an easy contaminant, so it fails adequate systems, and nowhere near enough for one controlling a dangerous contaminant, so it passes failing ones. Only a benchmark specific to the system reflects what that system actually needs to achieve.
Because the design figures and commissioning results are the benchmark the tests compare against - without them, a test has no proper reference and cannot confidently say whether current performance is what the system should achieve. The benchmark is what turns a measurement into a judgement, so the records are foundational.
The design specification and the commissioning data - the intended performance figures and the results confirming the system achieved them when new. These are the yardstick every future test relies on, so they are worth keeping with the system's documentation for its whole life.
Our thorough examination measures your system against its own design intent and commissioning benchmark - judging it by what it was built to achieve for your hazard, the only yardstick that properly applies.
