Control measures 3 - Engineering control

There are a number of common control measures which are called "engineering controls". These include enclosure, isolation and ventilation.

I - Enclosure

If a hazardous substance or work process cannot be eliminated or substituted, then enclose it so workers are not exposed to the hazards .
Many hazards can be controlled by partially or totally enclosing the work process. Highly toxic materials that can be released into the air should be totally enclosed, usually by using a mechanical handling device or a closed glove system that can be operated from the outside.

Examples of enclosures for fumes/vapours

Left you see the total enclosing of hazards, in the middle the partial enclosure is shown and to the right - ans example of a suboptimal practice - the hazard is not enclosed.

Machine guarding is another form of enclosure that prevents workers from coming into contact with dangerous parts of machines. Workers should receive training on how to use guarded machines safely. Some of the areas of a machine that can injure are: the point of operation (which is the area on a machine where work is actually being performed); pinch-points; sharp areas, such as blades; exposed electrical components, which can cause electrical shock or burns; presses, which can crush; rotating parts; flying chips and sparks.

Here are a few examples of types of machine guards:

  

Enclosure guards: prevent from coming into contact with the dangerous moving parts of a machine by enclosing the parts or forming a barrier around the dangerous parts. This type of guard also prevents broken and flying machine parts from hitting.
Interlocking guards: prevent from operating the machine if the guard is not in place, or automatically stop the machine if part of body enters a dangerous area. Photoelectrical or mechanical-sensing devices (such as a photoelectric eye) are examples of interlocking guards.

Automatic guards: actually pull or push the hands, arms, or body away from the danger zone as the work is being done.
Remote control, feeding, placement or ejecting guards: these control methods protect from dangerous points of operation. For example, a two-handed control requires both of hands to be on the controls (away from the danger zone) when operate the machine. This is a common method with punch/ stamping presses; a feeding mechanism may use an automatic device to feed material into the machine, so that no need to feed by hand.


II - Isolation

Isolation can be an effective method of control if a hazardous job can be moved to a part of the workplace where fewer people will be exposed, or if a job can be changed to a shift when fewer people are exposed (such as a weekend or midnight shift). The worker can also be isolated from a hazardous job, for example by working in an air-conditioned control booth.

It is also important to limit the length of time and the amount of a substance(s) to which workers are exposed if they must work in the hazardous area. For example, dust-producing work should be isolated from other work areas to prevent other workers from being exposed. At the same time, workers in the dusty areas must be protected and restricted to only a short time working in those areas. Isolation is also possible by using PPEs in the hazardous areas.

Isolating the work process or the worker does not eliminate the hazard, which means workers can still be exposed.


III - Ventilation

Ventilation in the workplace can be used for two reasons:

  • to prevent the work environment from being too hot, cold, dry or humid;
  • to prevent contaminants in the air from getting into the area where workers breathe. Generally there are two categories of ventilation: local exhaust ventilation and general ventilation. Whatever the type, ventilation should be used together with other methods of control.

Local exhaust ventilation usually uses suction, based on the principle of a vacuum cleaner, to remove pollutants from the air. There are two common types of local exhaust ventilation used in industry today:
(i) fumes are sucked into an open tank with side slots and into a closed system, through which they are then transferred to a disposal point away from the work places
(ii) fumes are sucked into a canopy hood which hangs over a contaminant and forced out through a ventilation duct. This type is very effective where the air pollutants have a high temperature, or if they rise in the air for another reason the figure on the right (top) demonstrate the suction at local level. The figure on the right (bottom) demonstrates the partial enclosure. (such as laboratory fume cupboards or screens placed around welders) combined with a local exhaust ventilation system is one of the best solutions for controlling toxic material. This type of system must operate as close as possible to the source of the hazardous agent to reduce it from spreading, yet at the same time allow access to the work process.

 

General ventilation generally used for keeping the workplace comfortable, is one of the least effective methods of controlling hazards but one of the most commonly used. The purpose of any general ventilation system is to remove contaminated air and replace it with "fresh" air. This system does not really remove hazardous agents from the air; it simply reduces the amounts in the air to levels that are considered "safe" for breathing. The effectiveness of a general ventilation system depends on several things, like: how quickly the hazardous agent is being released into the air; how much and how quickly fresh air is coming in; and how the contaminated air is being removed.
Unfortunately, many workplaces use general ventilation as the only source of ventilation.

Air-bricks, windows and doors may be opened to increase the general flow of air. However, these openings are often blocked or shut. Doors and windows are sometimes locked for security reasons, air-bricks may be blocked by excess stock being stored across them, etc. Without good general ventilation, hazardous agents in the air can accumulate (sometimes to dangerous levels), and the workplace may become very hot, difficult to work in and dangerous
Are fans a good source of ventilation? No. Fans can only help to remove fumes, dusts, etc., but they should not be used as a primary source of general ventilation and should never be used as a method of .removing toxic materials.

 

Does your workplace have some type of ventilation system in place that you assume is working properly? In many cases, the ventilation system is not effective because of poor design, lack of servicing, etc. Ventilation systems must be checked and serviced regularly. The best way to test how well the ventilation system in your workplace is working is with special equipment and personnel trained to use it. Unfortunately, the equipment and personnel can be hard to get. However, a simple way to see how well the ventilation extract system in your workplace is working is to sprinkle some dust or hold a piece of cloth near the exhaust outlet. If there is little air movement, then the ventilation system is not working properly and should be repaired. The photo above show the ventilation system off and on respectively.

  1. Engineering controls include enclosure, isolation and ventilation.
  2. If a hazardous substance or work process cannot be eliminated or substituted, then full enclosing is the next best method of control.
  3. Isolation can be an effective method of control if a hazardous job can be moved to a part of the workplace where fewer people will be exposed, or if the job can be performed at a time when fewer people will be exposed. Alternatively, the workers can be isolated from a hazardous job. Isolating a work process or a worker does not eliminate the hazard, therefore elimination is always a better choice than isolation.
  4. General ventilation can be used for keeping the workplace comfortable, and local exhaust ventilation for removing air pollutants. General ventilation is one of the least effective methods of controlling hazards. Ventilation systems must be checked and serviced regularly. Sprinkle some dust or hold a piece of cloth near the exhaust outlet to see if the air movement in your workplace is adequate.

 

 
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