Don’t let oil mist cloud health & safety


Filtermist CEO James Stansfield tells Technical Editor Steed Webzell about why machine shops should take heed of the HSE’s current campaign on metalworking fluids.

As part of a targeted campaign, the HSE (Health and Safety Executive) is warning businesses to make sure their staff are safe when working with metalworking fluids. HSE inspections are revealing poor performance around the control of metalworking fluids and coolants in businesses that use CNC machine tools. To stay on the right side of the law, oil mist extraction specialist Filtermist says machines shops need to implement suitable control measures.

Today’s modern machine shops typically use four basic types of metalworking fluids: straight oils, also known as ‘cutting’ or ‘neat’ oils; soluble oils; semi-synthetic fluids; and synthetic fluids. While each has its own specific properties there is a common denominator – all generate airborne mist particles. Oil mist is a danger to health and hence requires control within the workplace, enforceable by Control of Substances Hazardous to Health (COSHH) Regulations.

Sizing up the issue

Oil mist particles which are larger than 3.5 microns separate in the nose and throat, while particles smaller than 1 micron are absorbed into the bloodstream. Unfortunately, the throat, bronchial tubes and lungs retain particles between these sizes, potentially causing a variety of health hazards. Indeed, inhaling the mist generated by machining can lead to lung diseases such as occupational asthma and occupational hypersensitivity pneumonitis (also known as extrinsic allergic alveolitis).

Aside from the health issues, oil mist is flammable, accelerating the potential for disaster in the event of a fire. Oil mist also presents a slip hazard and  can cause problems with sensitive electrical equipment if ingress occurs – issues that can lead to costly machine downtime and repairs.

“Sadly, oil mist is a long-standing problem in machine shops that remains commonplace to this day,” reports James Stansfield, CEO of Filtermist, a company where he has been championing the merits of oil mist extraction for the past 25 years. “We’re still getting large, multiple orders for entire machine shops with no extraction.”


Although there is no defined maximum workplace exposure limit for oil mist, COSHH requires employers to reduce exposure to oil mist particles to ‘as low as reasonably practicable’: ALARP. There is a logical approach to the thought process here. Firstly, is it possible to eliminate metalworking fluids? If yes, great, but if not, it becomes necessary to implement appropriate controls.

“The burden of proof is on manufacturers, who must prove they did everything possible to remove the risk,” he explains. “There’s still a lack of education in the market. Some think if they can’t see a mist cloud they don’t have a problem, but certain mist is almost invisible  to the human eye. It comes in different particle sizes and volumes.”

According to Filtermist, machine tool manufacturers and their dealers are stepping up on this issue by recognising the requirement and taking responsibility. The company works very closely with machine tool suppliers, while also serving machine shops directly through retrofit applications.

“The latter business area is particularly busy at present because of the HSE campaign,” says James Stansfield. “We can usually offer machine shops an instant price to supply and install oil mist extraction as we have a huge database of machine tools. As part of HSE requirements, extraction requires fitting, commissioning and testing by a qualified engineer. If customers prefer, we have experienced engineers who can visit to perform spot tests and see what mist level is present. Where there is exposure to mist, it’s a legal requirement to carry out health surveillance even when preventative controls are in place. Businesses will need to involve an occupational health professional and workers should be encouraged to report any health symptoms that occur.”

Clean air solutions

There are three main types of oil mist extraction system, all of which are available from Filtermist. First are centrifugal units that spin the oil out using centrifugal force. Here, a perforated drum with special vanes rotates at high speed. The unit draws oil mist inside where it impacts on the vanes at high velocity. Drum pads assist the coalescing process and filter out stray particles. Centrifugal force pushes oil to the unit’s outer case where it drains back to the machine for re-use or collection, with clean air returned to the workshop through the top of the unit.

The second option is static media solutions that soak up the mist, ranging from basic units to high-end Absolent systems which include self-draining filter cassettes (no drain facility means the user does not need to constantly change filters). In principle, the unit draws air inside, with heavier particles falling to the bottom before being pumped out for collection or re-use. Polluted air then travels up through the first filter cassette which traps smaller particles. It’s possible to include a further filtration process, including HEPA filters, in particularly demanding applications.

And finally, electrostatic precipitation is another method used for removing oil mist particles. Electrostatic precipitators use an ioniser that produces an electrostatic charge which collects and traps air pollutants on an internal baffle plate. This type of filter is very effective for applications with fine particles.

“Although we try to simplify mist extraction for our customers, these systems require correct specification,” says James Stansfield. “It’s not just a case of buying a product off-the-shelf and fitting it yourself.  HSE guidance says such equipment requires fitting and commissioning by a competent LEV (local exhaust ventilation) installer. Machine shops need to get it right because we know for a fact that the HSE is actively knocking on doors as we speak.”

The HSE’s unannounced inspections look at how employers are ensuring the protection of workers from exposure to mist generated by CNC machines (see HSE guidance note HSG258 ‘Controlling airborne contaminants at work’). Any failures could lead to prosecution or liability to enforcement action. It could also expose the business to civil claims from employees or invalidate insurance claims. However, above all else, there is of course a moral obligation to protect employees.

The fight goes on

Despite stricter regulations than ever before, thousands of workers in the UK still contract occupational lung and other diseases, including cancer, each year. Some of these cases are attributable to exposure to dangerous levels of oil mist at work.

“We can help put this worry to bed by assessing the risk and deciding what precautions are necessary to prevent or adequately control exposure to oil mist,” concludes James Stansfield. “If required, we can also monitor the situation and maintain the systems accordingly.”


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