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Case study · Print and packaging · Solvent fume
A plant printing packaging for breakfast cereal used solvent-based inks, and extraction to keep the vapours they give off out of the air - and safely below the level at which they could ignite. The system passed, comfortably, and controlled the explosion risk well. But its carbon filter was quietly reaching the end of its life. Here is why that matters.
The site
The plant prints packaging for breakfast cereal at volume, using solvent-based inks on a flexographic line. As the ink dries, the solvents evaporate, and extraction over the print and drying stages carries that vapour away - out of the air the operators breathe, and away from any source of ignition.
Solvent printing is one of those processes where health and fire safety are the same problem seen from two sides. The vapour coming off the inks is hazardous to breathe, and it is flammable, so the extraction has to do two things at once: hold the exposure down and hold the vapour concentration well below the level at which it could ignite. Backing the extraction is a carbon-filter stage that cleans the air before discharge, and an LEL monitor watching the atmosphere.
The examination set out to confirm that the system was capturing the vapour effectively, keeping the air safely below the explosive limit, and that the abatement and monitoring that make that possible were in good order.
The hazard and the law
The vapour from solvent inks - volatile organic compounds such as ethanol, ethyl acetate and the propyl acetates - is hazardous to health: irritant to the eyes and airways, and narcotic at higher concentrations. Controlling that exposure is a COSHH duty, and where extraction provides the control it is LEV, due a thorough examination and test at least every 14 months.
But the same vapour is flammable, which brings the Dangerous Substances and Explosive Atmospheres Regulations (DSEAR) alongside COSHH. The safety principle is to keep the atmosphere below 25% of the lower explosive limit (LEL) - a quarter of the way to an ignitable mixture - so there is a wide margin before any risk of explosion. Extraction is the main way a print line achieves that, and an LEL monitor confirms it. So this one system discharges two legal duties at once: it protects health, and it keeps the workplace out of explosive territory. That dual role is why its performance, and the condition of its abatement, carry extra weight.
What we tested
We measured the capture and extract airflow at the print and drying stages, confirming the solvent vapour was drawn away at source before it could reach the operators or build up in the room. We checked the LEL monitoring - was the atmosphere being held comfortably below the 25% margin, and was the monitor itself calibrated and alarming correctly.
We then assessed the parts that make the system more than a fan: the ductwork and fan condition, and - the component that fails silently - the activated-carbon filter that cleans the extracted air before discharge. Carbon has a finite capacity, and once saturated it lets vapour pass straight through without any change in airflow, so its condition has to be assessed, not assumed. A qualitative check confirmed capture at the line.
What we found
| Check | Finding | Result |
|---|---|---|
| Capture at print / drying | Solvent vapour drawn away at source | Pass |
| LEL control | Atmosphere held comfortably below 25% of the LEL | Pass |
| Extract airflow / fan | Within benchmark; fan running true | Pass |
| Activated-carbon filter | Near end of service life - approaching breakthrough | Remedial |
The system did the important things well: it captured the solvent vapour at source, held the atmosphere comfortably below the 25% LEL margin, and ran to benchmark airflow - protecting both health and against explosion. The one action was the carbon filter, which was near the end of its service life and approaching breakthrough. Because a saturated carbon filter keeps passing air while silently ceasing to clean it, that is precisely the kind of thing that has to be caught by assessment rather than left to announce itself. A clean pass on control, with a planned filter change to keep the discharge clean.
The remedial action
The outcome
With the carbon media renewed and the LEL monitor confirmed, the plant has a dated record showing effective capture, a comfortable explosive-safety margin and clean abatement - the two duties this one system carries, both demonstrably met. The filter was changed as a planned action rather than discovered as a failure, which is exactly how it should go.
The point worth carrying away is that solvent extraction protects health and prevents explosion in the same breath, and that some of its most important parts fail invisibly. Capture and LEL control can be spot-on while a saturated carbon filter quietly stops cleaning the discharge, with no change in the way the system looks or sounds. Examining it on the 14-month cycle - with the LEL monitoring and the filter condition assessed, not assumed, and the media changed on a plan for a heavily used line - keeps both the COSHH duty and the DSEAR duty genuinely covered rather than merely appearing to be.
Sources and further reading
The duties, exposure limits and control standards described here come from the Health and Safety Executive. For your own process, always work from the current HSE guidance:
Questions
Solvent-based inks and coatings for packaging typically contain volatile organic compounds such as ethanol, ethyl acetate and the propyl acetates. As they dry they give off vapour that is both a health hazard - irritant and, at higher concentrations, narcotic - and flammable. Extraction keeps that vapour out of the operators' breathing zone and, just as importantly, stops it building toward a concentration where it could ignite.
The lower explosive limit (LEL) is the vapour concentration below which there is too little fuel in the air to ignite. The widely used safety rule under DSEAR is to keep the atmosphere below 25% of the LEL - a quarter of the way to an explosive mixture - so there is a large safety margin. Extraction is the main way a printing line holds the vapour down to that safe fraction, and the LEL monitor is what confirms it.
Yes, and that is the key point. It protects health by keeping VOC exposure down, and it protects against fire and explosion by keeping the flammable vapour well below the LEL. The same system discharges two legal duties - COSHH for the exposure and DSEAR for the explosive atmosphere - which is why its performance matters doubly.
On a solvent system the activated-carbon filter adsorbs VOCs from the extracted air before it is discharged, reducing emissions. Carbon has a finite capacity: once it is saturated it stops adsorbing and lets vapour pass straight through - 'breakthrough'. It does not fail by stopping the airflow, so the system keeps running normally while its abatement quietly stops working. That is why the filter's condition has to be assessed rather than assumed.
Because a pass on capture and LEL control does not mean every component is fresh. Here the extraction captured well and held the vapour comfortably below the LEL, but the carbon filter was near the end of its service life and approaching breakthrough. Replacing it before it saturates keeps the discharge clean and the system fully effective - a planned change rather than a surprise failure.
At least every 14 months under COSHH, with the LEL monitoring and the carbon filter condition checked as part of keeping the system both healthy and explosion-safe. Because the carbon filter degrades with use rather than age alone, a heavily used line may need its media changed more often than the test interval - the examination tells you where it stands.
Tell us your capture points and the process they control, and we will quote the thorough examination and test to COSHH and HSG258.
