Manufacturing workshops can generate serious volumes of dust, fume, and vapour during normal operation. Local Exhaust Ventilation (LEV), the general term for dust, fume, and mist extraction systems, isn’t there to simply “keep the air moving.” Its job is to capture and contain contaminants at the point they’re created, before they ever reach a worker’s breathing zone. General ventilation dilutes; LEV controls at source. That distinction matters, because most of the mistakes below come down to a system that’s moving air without actually controlling exposure.
Lots of businesses install an LEV system and assume it will keep performing perfectly forever without any further attention. When performance quietly degrades, it’s difficult to spot and workers can end up breathing in contaminated air well above safe levels without anyone noticing, which is a direct COSHH compliance risk as well as a health one.
Knowing where LEV systems typically go wrong can help you catch problems in your own setup before they become serious. If you think your system might be under-performing, the team at Vent-Tech can give you a straightforward, expert assessment.
1 & 2. Wrong Hood Positions and Undersized Systems
One of the most common issues we see on factory floors is a hood positioned too far from the process. If the hood sits outside the effective capture zone, contaminants escape into the general workshop air instead of being drawn into the system, meaning the extraction is running, but not actually protecting anyone.
Other times, the system itself is undersized for the volume of contaminants being produced. Sometimes it was correctly sized originally, but as processes change or production ramps up, it’s no longer fit for purpose. Either way, weak airflow means the system can’t generate the capture velocity needed to pull dust, fumes, or mist away from the worker’s breathing zone.
Avoiding this starts with a proper design, carried out before installation, not adjusted after the fact. This is why LEV good practice (set out in BESA’s TR40 guidance) treats design as its own distinct stage, with sign-off before anything is built.
3. Poorly Considered Duct Layouts
Another frequent mistake is a duct run with too many sharp bends or excessively long straight sections. Poor layout slows the air velocity inside the ductwork, which reduces the system’s ability to keep material airborne and moving.
When air velocity drops too low, heavier dust starts to settle inside the ducting. Over time this causes blockages, and for combustible dusts, a settled dust layer inside ductwork is a genuine fire and explosion risk, which is exactly what DSEAR risk assessments are designed to catch.
Keeping duct runs as short and direct as possible, with minimal bends, is the most reliable way to maintain transport velocity. At Vent-Tech, we design the duct route first and then select the fan to suit it, not the other way round, because a fan can’t compensate for a badly laid-out system.
4. Skipping Statutory Testing and Maintenance
A fan making noise and spinning tells you almost nothing about how well a system is actually performing. Airflow can drop significantly, filters clog, belts slip, ducts leak, long before it’s audible.
Under COSHH Regulation 9, every LEV system must undergo a Thorough Examination and Test (TExT) at a maximum interval of 14 months (some processes, particularly those involving higher-risk substances, require more frequent testing, this is determined by risk assessment). Skipping this isn’t just a maintenance oversight, it’s a legal compliance gap. A TExT checks system performance against the original design data and confirms whether the contaminant is still being controlled below the relevant Workplace Exposure Limit (WEL), as set out in EH40/2005.
Getting this done on schedule catches minor faults while they’re still minor, before they become a system failure or an HSE enforcement issue.
5. Moving Machinery Without Reassessing the System
Changing your factory floor layout without reassessing the LEV system is a fast way to create problems. Adding a machine to an existing line, or moving one, changes the airflow demand across the whole system, and can starve other connected hoods of the capture velocity they need, even if nothing near them physically changed.
When suction drops in one part of a shared system, the cause is rarely obvious just by looking. Without proper airflow data, there’s no reliable way to know whether workers elsewhere on that system are still being protected.
Fitting monitoring systems gives you a continuous, objective read on system performance and an early warning if suction drops, keeping the system verifiably compliant, not just apparently fine.
Conclusion
Avoiding these basic mistakes is the easiest way to protect your team and save your business money. From poor hood positioning to skipped testing, ignoring small issues can quickly turn into a system that’s running but not actually protecting anyone, and a compliance problem you don’t find out about until it’s serious.
Making sure your hoods are correctly positioned, your ducting is well laid out, and your system is tested on schedule will keep your workplace safe and your business compliant. Investing in your LEV system now avoids unexpected breakdowns, keeps your workforce protected, and keeps your production line running without interruption.
If you think your system is losing power or you want an expert opinion on your workplace air quality, get in touch. Head over to our contact page to speak with our friendly team about what your factory needs.