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Containment Fundamentals

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Whereas the UK COSHH rules show a clear hierarchy of control measures:

  • Elimination at the source
  • Substitution with a less hazardous material or form
  • Reduction of the quantity below critical limits
  • Engineering controls to prevent intolerable operating staff exposure (contained handling)
  • Administrative controls
  • Use of Personal Protection Equipment (PPE)

In many other countries no legislation enforces this hierarchy. Most of the western countries will monitor the conditions under which operators have to work in the countries from which they import as it is seen as highly unethical to support practices that create health and safety risks in other areas of the world.

There are good reasons for this order of preference, especially that PPE should only be used as a last resort (for maintenance; for necessary, but unforeseen interactions; or if any other method further up in the hierarchy has been considered without success). Why is this?

Firstly, PPE only protects the operator. The hazardous substance is not contained, which means that the associated problems are increased: changing of filters, cleaning of rooms and equipment, inside and outside, become major containment issues.

Additionally, depending on the PPE system used, the levels of protection are limited. For systems taking the air from the room via a filter system, the best filters (P3 according EN 149) offer NPFs (Nominal Protection Factors) of 30. This means that if the dust concentration in a room is 3 mg/m³ (typical for open production), at best the concentration inside the system will be 100 µg/m³. Additionally, the lifetime of the filter element is limited because of the high dust loading.

The situation is different if air-fed systems are used. These systems can provide better protection levels, but there are still some areas of concern. The performance of these systems is very operator-dependant and in most countries it is not acceptable to put the responsibility for his health (or even life) into an operator’s own hands. The working conditions inside an air-suit are unpleasant: hot, humid with poor visibility and limited movement. This results in low levels of operator efficiency, and the need to take frequent breaks, reducing efficiency even further.