Health & Safety

Oil mist and oil smoke arise in a number of various manufacturing operations. Before we can take the correct measures to overcome the risks and harm that these substances cause, we need to know specifically what oil mist and oil smoke really are.

In the manufacturing industry, oil mist arises especially during metal-cutting machining, which is a comprehensive term for turning, milling, grinding and boring, etc. Oil mist arises when oil or water mixed with concentrated cutting fluid, so-called emulsion, is used for cooling, lubricating or chip removal.

From oil mist to oil smoke

With high speed and pressure, the oil drops get very small (<1 µm) and the amount of oil in the air is often high. In such operations, oil smoke occurs in a larger scale.

As machining operations are carried out, these fluids are emitted in the form of aerosols and smoke to the surrounding air. It is, of course, unhealthy to breathe these substances.

The National Board of Occupational Safety and Health has therefore drawn up specific limit values for this. The current limit value for the emission of aerosols to industrial premises is 1 mg/m³.

What are the risks?

The risks that are most often associated with large concentrations of oil mist or oil smoke are the following:

• Oil mist can contain small metallic particles that can give rise to respiratory problems.
• Skin problems, including oil acne and eczema.
• Increased risk of slipping – oil mist eventually settles on the floor.
• Deteriorated indoor air caused by oil accumulating on surfaces inside the ventilation system impairing its function and fouling the air.
• Generally unclean environment due to the oil attracting other impurities causing them to stick to machines and other equipment.
• Aerosols harm the electronics in modern metalworking machines.

How to deal with oil mist and oil smoke problems?

The most common and effective method of collecting oil mist / oil smoke is at the source, i.e. directly at the metalworking machine. This is possible both in the case of completely enclosed machines and open machines.

In an enclosed machine, sub-atmospheric pressure is created in the space where the machining operations take place. The oil-laden air is sucked out of the enclosure and conveyed through a duct to the filter unit. After the air has been filtered, it is returned to the premises or flows further to a heat exchanger.

If open machines are installed, it is common to try to capture oil mist/smoke in some kind of hood or superstructure and from there convey it through a duct to the filter unit.

Dust, or airborne particles, consists of minute particles that can remain freely suspended in the air and distributed over long distances. Such particles are 100 µm in size or smaller, i.e. one tenth of a millimetre. However, larger particles which are not airborne can also be considered dust. Dust is generated in a number of various industries, such as the woodworking, metal-working, cement manufacturing, mineral wool manufacturing and plastics industries.

Absolent focuses on dealing with dust that is generated in the engineering industries. The following are typical operations that generate dust:

• Welding
• Laser and plasma cutting
• Dry grinding
• Sand blasting
• Painting

In short: most operations that handle, machine or process dry materials.

Risks and Discomfort

Dust particles have acute effects on a person's respiratory passages. Worst affected are elderly people and persons with respiratory diseases.

The particles may be carcinogenic in themselves but they may also be carriers of carcinogenic substances.

Several factors contribute to the hazardousness of dust, for example the particle size, type of dust and type of accompanying substances in the dust.

Inhaled particles larger than 10 µm normally get caught in the cilia inside the nose and do not reach the lungs. Particles between 2.5 and 10 µm generally seat themselves in the upper respiratory tract where they can cause or aggravate asthma, pneumonia and bronchitis. Several studies have shown a connection between increased particle content in the air and an increasing frequency of deaths and hospital admissions. The effects on health can be broken down into three groups: diseases of the respiratory tract, cancer and cardiovascular diseases.

Dust emissions have impact on the environment in the form of dusting and air pollution. Furthermore, dust may carry poisonous substances such as heavy metals and organic environmental toxins. These in turn have an impact on both the soil and water in different ways.

Dealing with Dust

A number of conditions must first be considered for the evaluation of a suitable air purification technique and for choosing a cost-efficient solution. Typical conditions to be considered are airflows, dust content, type of dust, where contaminants arise, etc.

Air purification involves the separation of particles from the air. Dust extraction hoods or direct dust extraction on enclosed machines are commonly used and this involves conveying air containing impurities to a dust filter where the air is purified. The air is then discharged into the premises or to the open air outside. Because, in most cases, this involves large airflows, heat exchangers are generally used for recovering heat from the purified air as a means of reducing power consumption.

Textile filters, such as pleated cartridge filters, have a high dust collecting efficiency, as much as 99% or more in many cases and their efficiency for collecting small particles is also high. The performance of filters depends on a combination of several factors: filtering capacity, diffusion, forces of inertia, etc. Textile filters are well suited for arresting particles of 1 – 100 µm in size.

Reference:

Länsstyrelsen Västra Götalands Län. (The County Administrative Board of Västra Götaland County) Rapport 2004: 56, Partiklar och Stoft – en kunskapsöversikt. (Particles and Dust – A Knowledge Survey)

ISSN 1403-168X, Version 2004-05-24