Phoenix Journal · LEV Testing
That mid-afternoon fog is often the room, not the person. Here is what the evidence says about how stale, poorly ventilated air quietly slows the way your team thinks - and how extraction keeps it clear.
We tend to blame a foggy afternoon on a poor night's sleep or one coffee too few, but very often the real culprit is the air in the room.
Air quality is usually framed as a health and safety issue - and it is - yet its most immediate effect is something far harder to spot on a spreadsheet: the way it quietly blunts how well people think. In a busy commercial kitchen, an open-plan office above a restaurant, or a workshop with the doors shut against the cold, stale air builds up long before anyone feels unwell. Concentration slips, decisions take a fraction longer, and mistakes creep in. None of it announces itself. That is exactly what makes indoor air quality worth taking seriously as a performance question and not only a compliance one.
This piece looks at what the current UK and international evidence actually says about air quality and cognitive performance, where the pollution in your building really comes from, and how extraction and ventilation - the systems Phoenix Duct Clean works with every day - keep the air clear enough for people to do their best work.
The clearest recent work comes from the Global CogFx study, which tracked more than 300 office workers across six countries including the UK, monitoring the air around them while they completed cognitive tasks. The pattern was consistent and, frankly, sobering: for every 500 parts per million rise in carbon dioxide, response times slowed by roughly 1.4 to 1.8 per cent and the amount of work people got through fell by around 2.1 to 2.4 per cent. Small numbers on their own, perhaps, but they stack up across a shift, a team and a year.
The most striking finding was what the researchers did not find: there was no comfortable lower threshold below which the effect simply disappeared. Even under 1,000 ppm - a level most building guidance treats as perfectly acceptable - people still performed better when the air was fresher still. That matters because carbon dioxide itself is not really the villain here. It is a proxy. When CO₂ climbs, it is telling you the space is not getting enough fresh air, and everything else that builds up in poorly ventilated air - fine particles, cooking by-products, volatile compounds - is rising alongside it. CO₂ is simply the easiest thing to measure, which is why HSE points to it as a practical indicator of whether a room is adequately ventilated.
For context, HSE guidance suggests the fresh-air supply in a workplace should not normally fall below 5 to 8 litres per second per person, while CIBSE recommends around 10 litres per second per person for a general office. When ventilation drops below that, CO₂ drifts up past 800 and then 1,000 ppm, and the cognitive tax the CogFx study measured starts to bite.
In an ordinary meeting room, the main pollutant is simply the people in it - we exhale carbon dioxide, and without enough fresh air coming in, it accumulates through the day. But in the environments Phoenix Duct Clean works in, the picture is more loaded. Commercial cooking throws off a genuine cocktail: fine particulate matter from frying and grilling, nitrogen dioxide from gas burners, grease-laden vapour, and a range of volatile organic compounds. Much of this is invisible, and a lot of it is small enough to be breathed deep into the lungs and, the emerging research suggests, to reach the brain.
Fine particulate matter is the one to watch. The World Health Organization tightened its air quality guidelines in 2021, recommending an annual average for PM2.5 of just 5 micrograms per cubic metre, precisely because the evidence on long-term harm - including to cognition - kept strengthening. A commercial kitchen that vents poorly, or an office sitting in the plume of one, can sit well above that for hours at a time. Staff working through it will not collapse; they will just be a little slower, a little more irritable, a little more prone to the small errors that turn into bigger ones.
This is where extraction stops being a comfort measure and becomes a performance one. A kitchen extraction canopy and its ductwork exist to capture that grease, particulate and vapour at source and remove it before it drifts back into the breathing zone. When the ducting is clogged with grease, or the fans are struggling against a system that has not been cleaned, capture falls off and the contaminated air lingers - not just over the range, but through the pass, into the dining space and up into any offices above. The same logic applies wherever a process generates airborne contaminants, which is exactly the ground that local exhaust ventilation, or LEV, is designed to cover.
The encouraging part is that this is a solvable problem, and the fixes are largely mechanical rather than behavioural. You cannot ask a team to concentrate their way out of stale air, but you can make sure the systems meant to clear it are actually doing their job. That starts with keeping extraction and ductwork clean so it captures contaminants at full strength, and it runs through to making sure any LEV that controls a hazardous process is examined and proven to work.
Under the Control of Substances Hazardous to Health Regulations - COSHH Regulation 9, backed by HSE's HSG258 guidance - any LEV system must undergo a thorough examination and test by a competent person at least once every 14 months, with records kept for a minimum of five years. Higher-risk processes need it more often. That statutory check is not box-ticking: it confirms the system is still pulling contaminants away from the people who would otherwise breathe them, which is the whole point. Get it right and you protect health and hold onto the cognitive sharpness that stale, loaded air quietly erodes.
It is worth remembering that this reaches beyond the kitchen itself. The same relationship between clean air and clear thinking shows up on the shop floor, where we have looked at the link between air quality and workshop productivity, and in busy public spaces such as when you manage air quality in a gym or leisure centre. Wherever people work, gather or exert themselves, the air they breathe is quietly setting a ceiling on how well they can perform - and that ceiling is one you have real control over.
The practical takeaway is simple. Treat air quality as an ongoing operational input, not a one-off installation. Keep your extraction clean, ventilate generously, watch your CO₂ as a cheap early-warning signal, and make sure your LEV is tested on schedule and proven effective. Do that and you are not only meeting your legal duties - you are giving everyone in the building the quiet, unglamorous advantage of air that lets them think straight.
Questions
When a space is under-ventilated, carbon dioxide and other pollutants build up faster than fresh air can dilute them. Research such as the Global CogFx study found that for every 500 ppm rise in CO2, people responded more slowly and got through less work. Fine particles and cooking by-products compound the effect, so staff stay conscious and functional but lose a measurable edge in speed, accuracy and decision-making across a shift.
CO2 is best treated as an indicator of ventilation rather than a poison in its own right. HSE points to it as a practical signal, and readings consistently below 800 to 1,000 ppm generally suggest a space is adequately ventilated. The CogFx research suggests fresher is better even below that, so lower is preferable wherever the work is cognitively demanding. Aim to keep fresh air at around 10 litres per second per person for a general office.
Local exhaust ventilation captures fumes, dust and vapour at source before people breathe them, which directly affects how clean the air in the room stays. Under COSHH Regulation 9, an LEV system must be thoroughly examined and tested by a competent person at least every 14 months. A test that proves your extraction is working is really a check that the air your team is breathing is not quietly undermining their concentration and health.
Phoenix Duct Clean · by the numbers
Phoenix examines and tests local exhaust ventilation to HSG258 and COSHH - measured, reported and certificated, UK-wide.