Home / LEV Testing / Guide
LEV testing - the specification
Buying an LEV system without first writing a specification is buying blind - trusting that whatever is installed will do the job, with no defined standard to hold it to. A clear specification, setting out what the system must control and to what standard, is what gets you extraction that actually works and, just as important, can be proven to work at commissioning and every test after.
The short answer
An LEV specification is the document that defines, before you buy, what the system must do: which processes and contaminants it has to control, the performance it must achieve to control them (the airflow and capture velocity each hood needs), and the standards it must meet. Writing it first matters because it turns the purchase from a hope into a defined requirement - the supplier knows exactly what to deliver, and you have a standard to check the delivered system against. It is also what makes commissioning and future testing meaningful, because it sets out the performance the system was meant to achieve, which is the benchmark everything is measured against.
Buying without a spec is buying blind
It is surprisingly common to buy LEV the wrong way round - to have a system installed and simply trust that it will do the job, without ever having defined what the job actually is. This is buying blind. Without a specification, there is no agreed statement of what the system needs to control or how well, so there is nothing concrete to hold the installed system to. If it turns out to under-perform, there was never a defined standard it was supposed to meet, which makes it hard to say it fell short of anything. The purchase rests on hope rather than a requirement.
Writing a specification first turns this around. It defines the requirement before anything is bought - what the system must achieve to control the hazard - so that the purchase is made against a clear standard rather than a vague expectation. This benefits everyone: the supplier knows exactly what they are being asked to deliver, and you have a defined requirement to judge the delivered system against. A specification is, in essence, the difference between buying a system you have specified to do a defined job and buying whatever a supplier chooses to install and hoping it suffices. For a control that has to genuinely protect people, defining the requirement first is the sound way to buy.
What the specification defines
A good LEV specification sets out several things. First, what the system must control: the processes it has to serve and the contaminants they release - the dust, fume, vapour or mist that the extraction must capture. This is the foundation, because everything else follows from what is being controlled. Understanding the hazard - what it is, how much is produced, where and how it is released - defines what the system has to deal with, and a specification that is vague about this cannot properly define the system needed to control it.
Second, the performance the system must achieve: the airflow and the capture velocity each hood needs to control its contaminant effectively. This is where the specification becomes concrete and measurable - not just that the system should extract, but that it should achieve the specific performance that controls the particular hazard. Third, the standards the system must meet - the recognised standards of design and performance that a properly engineered LEV should satisfy. Together these turn the specification into a definite, checkable requirement: this system, serving these processes, must achieve this performance, to these standards. That is a requirement a supplier can build to and a delivered system can be measured against.
Why it needs real design input
Writing a specification that genuinely captures the right performance is not something to guess at - it takes real understanding of LEV design and of the hazard being controlled. Determining the airflow and capture velocity a hood needs to control a particular contaminant, and the system needed to deliver that across all the processes, is a design task requiring expertise. This is why LEV design is itself a recognised competence, with its own qualification: getting the specification right means working out what the system actually has to achieve, which is a technical judgement about the hazard and the ventilation needed to control it.
This means a good specification often benefits from proper design input rather than being written casually. Someone competent in LEV design can translate the processes and hazards into the performance the system must achieve, so that the specification defines a system that will genuinely control the exposure - not just any extraction, but extraction sized and configured for the actual job. Skimping on this, and specifying vaguely or leaving it entirely to the supplier's discretion, risks a system that is not properly matched to the hazard. So the effort of specifying properly, with real design understanding behind it, is what ensures the specification defines a system that will actually work rather than one that merely exists.
Why the spec makes testing meaningful
A specification does not just help you buy well - it makes the whole later life of testing the system meaningful, because it sets out the performance the system was meant to achieve. That specified performance becomes the benchmark: at commissioning, the installed system is checked against the specification to confirm it delivers what was required, and at every future thorough examination, the system is measured against that same intended performance to see whether it is holding up. Without a specification, there is no clear statement of what the system should achieve, which weakens commissioning and every test after.
So the specification is the origin of the benchmark that runs through the system's whole life. It defines what the system must achieve; commissioning confirms it achieves it; and future tests check it still does. Each stage relies on the specified performance as the reference. This is why the specification is foundational not just to the purchase but to knowing, ever after, whether the system is working - it is the standard the system is held to from the day it is installed. Buying without one means not only buying blind but also testing blind later, with no clear intended performance to compare against. Writing the specification first is what gives both the purchase and the testing something solid to stand on.
The takeaway
Buying LEV without a specification is buying blind - trusting that whatever is installed will suffice, with no defined standard to hold it to. A specification, written first, defines the requirement: what the system must control (the processes and contaminants), the performance it must achieve (the airflow and capture velocity each hood needs), and the standards it must meet. That turns the purchase from a hope into a definite requirement a supplier can build to and a delivered system can be measured against.
Because specifying the right performance takes real understanding of LEV design and the hazard, a good specification benefits from proper design input rather than being written casually - it is what ensures the system is matched to the job. And the specification does more than guide the purchase: it sets the performance the system was meant to achieve, which becomes the benchmark for commissioning and every future test. Specify first, and everything follows - a system that works, and the standard to prove it does, for the system's whole life.
Questions
The document that defines, before you buy, what the system must do: which processes and contaminants it has to control, the performance it must achieve to control them - the airflow and capture velocity each hood needs - and the standards it must meet. It turns the purchase into a defined requirement rather than a hope.
Because buying without one is buying blind - there is no agreed statement of what the system must control or how well, so nothing concrete to hold the installed system to. A specification defines the requirement first, so the supplier knows what to deliver and you have a standard to check the delivered system against.
What the system must control - the processes and the contaminants they release; the performance it must achieve - the airflow and capture velocity each hood needs to control its contaminant; and the recognised standards of design and performance it must meet. Together these make a definite, checkable requirement.
It benefits from it. Determining the airflow and capture velocity a hood needs to control a particular contaminant is a design task requiring real understanding of LEV and the hazard - LEV design is itself a recognised competence. Proper design input ensures the spec defines a system genuinely matched to the job.
It sets the performance the system was meant to achieve, which becomes the benchmark. At commissioning the installed system is checked against the spec; at every future examination it is measured against that intended performance. Without a spec there is no clear standard, which weakens commissioning and every test after.
You buy blind and test blind. There is no defined standard the system was meant to meet, so if it under-performs there is nothing to say it fell short of, and later testing has no clear intended performance to compare against. Writing the spec first gives both the purchase and the testing something solid to stand on.
A clear specification defines the performance your LEV must achieve - the benchmark our commissioning and thorough examination measure against, so the system is proven to do what it was bought to do.
