Diagnostics & problems
A solvent smell while the extraction runs means vapour is reaching noses instead of the hood. But smell is a poor gauge in both directions: for some substances you smell them only after you are overexposed, and for others you stop noticing at all.
The short answer
If a solvent or process odour hangs in the air while the extraction is running, the plain reading is that capture is failing: vapour is escaping into the room and reaching people's breathing zones instead of being drawn into the hood. That much is a genuine warning worth acting on. What the smell cannot tell you is how much vapour is present, because odour is an unreliable gauge in both directions.
The detail
For some substances the odour threshold, the concentration at which you first notice a smell, sits above the workplace exposure limit. Benzene is a well-known example: people often cannot smell it until they are already above the level meant to protect them. So being able to smell such a substance can mean you are already overexposed, while not smelling it proves nothing about safety. For other substances the reverse is true and you detect them far below any harmful level, which is its own kind of false alarm.
On top of that, the nose adapts. Olfactory fatigue means that a constant smell fades from awareness within minutes, so a workshop where staff say the smell has gone may simply be one where everyone has stopped noticing a steady concentration. Between odour thresholds that do not line up with exposure limits and a sense that switches itself off, smell is useful only as a rough prompt. The moment it prompts, the right response is to measure, not to reassure yourself that it has faded.
What it means for you
The escape that lets you smell solvent usually comes from a small number of causes: a hood that is too far from the release, mispositioned or the wrong type for the job; a cross-draught from a door, fan or open shutter that peels the plume away from the hood; a fan that has weakened; or a leaking duct that has bled off the pull. A thorough examination checks hood type and position against the work, uses smoke to show where the air actually goes, and measures capture velocity and airflow against the design to find which of these is at work.
Where there is any doubt about the dose people are receiving, COSHH Regulation 10 exposure monitoring puts a measured figure on the vapour in the breathing zone, which is the only way to compare it to the workplace exposure limit with confidence. The examination fixes the capture; sampling confirms whether exposure is now under control. Treating a persistent smell as something to be measured rather than tolerated is the difference between catching a failing hood early and discovering it in a health record later.
The service behind the guide
We treat a persistent smell as escaping capture to be traced, not tolerated. Smoke and airflow measurement show where the plume is getting away, and where needed we arrange sampling to measure the dose.
Questions
It strongly suggests capture is failing, because vapour is reaching the breathing zone instead of the hood. The smell is a genuine prompt to examine the extraction, even though it cannot tell you how much vapour is present.
No. For some substances the odour threshold is above the exposure limit, so you may be overexposed before you smell anything, and the nose adapts to a constant smell within minutes. Absence of smell is not proof of control.
Because odour thresholds do not line up with workplace exposure limits, and olfactory fatigue makes a steady smell fade from awareness. Smell is a rough prompt at best; only measurement compares exposure to the limit.
Commonly a hood that is too far from the release or the wrong type, a cross-draught from a door or fan that peels the plume away, a weakened fan, or a leaking duct. A thorough examination and smoke test identify which.
Where there is doubt about the dose, yes. COSHH Regulation 10 exposure monitoring measures the vapour in the breathing zone so it can be compared to the workplace exposure limit, confirming whether exposure is under control.
Phoenix Duct Clean · by the numbers
A lingering smell is a prompt to examine the extraction and, where needed, sample the air. Call to book a thorough examination that finds the failing capture behind the smell.