Health and Safety
Oil Mist - A Problem of Industrial Proportions
Oil has long been an integral part of various industrial manufacturing processes. From machining to forging and stamping, neat and emulsion (water and oil mix) oils are increasingly relied upon by modern machine tools.
But this additional demand for oil has created a new problem for manufacturers worldwide. As the cutter rotates, swarf and heat are an unwanted by-product, which, when combined with the agitation of the coolant, causes a mist aerosol to emanate from the machine. This mist can be composed of a whole host of potentially harmful ingredients:
- Hydraulic oil
- Lubricating oil
- Tramp oil
- Any additives added to the coolant to prolong its life
- Slivers of the metal been machined
- Particulates and coatings from the cutting tool and any coatings
- Other particulate resident in the coolant tanks, pipes etc such as bacteria and spores
Whilst additives which are added to prolong the coolant life kill any present bacteria, the decomposing bacteria can create endotoxins, which themselves can represent a potential hazard when inhaled.
This aerosol cocktail leaves the machine and ascends to the ceiling of the facility, where it may stay for some time depending on the size of the mist droplets. Whilst there it dulls the lighting, coats the roof, girders, electrical bus bars and any heating elements in oil, and can severely damage the ventilation system. When descending it will coat walls and machines, before entering an employee’s working environment where it may be inhaled. Eventually, the remaining mist settles on the floor, creating potential slip hazards in the form of randomly dispersed pools of oil. This process is not isolated to one small area of a facility, however. As air flows around a workshop, the mist can be carried over vast distances, meaning that these problems can be experienced many metres away from the original source.
A little known, and highly-expensive fact is that the metal slivers contained in the mist can ingress into the electronic cabinets of machine tools, settling on the delicate drive boards and cause arcing. The replacement of damaged boards and associated machine down time is a cost being incurred by more and more manufacturers.
Machine Tools Cannot Cope
The majority of older machine tools possess no mechanisms for containing the mist and the aerosol simply emanates from the machine into the environment. And whilst many newer machines feature a cabin to help suppress the release of oil mist into the facility atmosphere, these cabins can provide insufficient defence in the current manufacturing climate.
To reduce cycle times and remain competitive, manufacturers are demanding more and more from their machine tools. With high spindle performance and cutting feed rates, coolant pressures are reaching 300 Bar. But when the machine’s doors are opened by the operator to inspect or change the component, or to change the tool, large quantities of oil mist escapes into the wider factory environment. In addition, a positive pressure within the cabin forces the mist to seep out from any available openings into the facility.
A Filtration System or just an Extractor?
We often encounter companies employing outdated oil mist filtration systems which were better than nothing when first installed, but are simply inadequate for the demands being placed upon them by modern manufacturing processes.
These obsolete systems typically have very low efficiencies, extracting, for example, 100 mg/m³ of oil mist from the machine tool, but releasing between 50 – 90 mg/m³ back untreated into the factory atmosphere. In reality, these traditional systems are simply extractors – removing the mist from the machine cabin, and venting it out into the facility. This, coupled with the fact that they often require regular maintenance and servicing to sustain even a low efficiency, means in many cases they offer little or no real protection at a high cost.
Oil Wash Mist - an often overlooked hazard
Typically, at the end of manufacture, a component is subject to a vigorous cleaning process to remove the oil and debris accumulated in the production process. The emissions generated by this washing process have identical constituents to the mist produced by machine tools, except with one major difference – the hot water and steam used to cleanse components provide an ideal breeding ground for bacteria. This means that in addition to the oil, metal slivers, particulate and spores, the mist generated in this stage can often contain high levels of potentially hazardous bacteria. In spite of this, we find that most manufacturers do not utilise oil mist filtration at this stage.
Causing a Global H&S Re-Think
For a long time, national Health and Safety organisations have issued guidance to their respective countries on safe levels of oil mist in industrial workplaces. Generally, the publicised safe level for emulsion mist was 1mg/m³. This level, however, was based upon ‘good practice’ and not on the potential impact upon health. A marked increase in the number of lung damage cases has urged many H&S organisations to investigate further the potential link between oil mist and serious respiratory conditions such as industrial occupational asthma and extrinsic allergic alveolitis.
In the UK, for example, the Health and Safety Executive (HSE) conducted a two year study into problems at the Rover Powertrain facility in Birmingham, where over a hundred workers were found to have sustained a variety of respiratory diseases linked to metalworking fluids. Findings from the study caused the HSE to remove all guidance figures for exposure to oil mist, recommend that risk assessments be completed, and that when surveying the atmosphere, the total amount of mist in the air should be measured rather than simply the metalworking concentrate.
For further information and helpful advice on handling of metalworking fluids click here.
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On its way through a filter media 4 mm thick, a 0.1 μm particle will travel 4000 times its own diameter.