DREHMO EX-proof Actuators – Basic Principles
Explosion
An explosion is a sudden oxidation or disintegration reaction with a very high reaction rate which generates an increase in temperature or pressure, or both at the same time. The most common are reactions of combustible gases, vapours or dusts with the oxygen in the air.
Conditions for an explosion
For explosions to occur in atmospheric air, three factors need to come together:
- combustible material
- oxygen (air)
- ignition source
In production plants and places of work, hazardous areas for explosions can form when the first two prerequisites for an explosion are fulfilled. Typical hazardous areas occur in chemical factories, refineries, paint factories, paint shops, purification plants, mills and stores for milled products and other combustible dusts, in tanking and loading plants for combustible gases, liquids and solid matter and in the mining industry.
The first two components - combustible material and air - must be present in sufficient quantities for a potentially explosive atmosphere to form. The oxidation reactions are mostly linked to warming and pressure increase, thereby fulfilling the criteria for an explosion.
Protection principle
These are principles that eliminate systems, devices and components as ignition sources.
Ignition sources that originate from friction and impact sparks and electrostatic charges are to be eliminated on explosion-protected equipment through the selection of suitable materials and through design measures. This is proven and confirmed by corresponding tests.
Four protection principles can eliminate equipment as an ignition source. One fundamental prerequisite for all protection principles is that the parts in direct contact with the potentially explosive atmosphere must be unable to achieve an inadmissible temperature in view of the ignition temperature of the materials present at the place of use. The ignition temperature is therefore significant for all protection principles.
Protection principles can be applied equally to electrical and non-electrical devices and to gases and dusts. The principles permit designs in various safety categories in accordance with the Explosion Protection Directive 94/9/EG:
- Category 1 - with highest protection level and therefore with a very high degree of safety
- Category 2 - with a high protection level and therefore with a high degree of safety
- Category 3 - with a normal protection level and therefore with a normal degree of safety.
Construction regulations for explosion-protected systems, devices and components - equipment
Dangers that occur when working with combustible gases, vapours and dusts are based on consistent chemical and physical processes. These dangers can therefore only be tackled in a consistent manner.
The International Electrotechnical Commission (IEC), the European Committees for Standardization (CENELEC and CEN), the German Commission for Electrical, Electronic & Information Technologies of DIN and VDE (DKE) and DIN now issue almost fully consistent requirements.
Their observance is required of manufacturers and operators and, in the event of increased protection requirements, monitored by recognized testing offices and authorities.
Manufacturers of explosion protected systems, devices and components, builders and operators of plants work together to ensure that the prerequisites for the safe operation of plants in potentially explosive areas are met.
DREHMO actuators fulfil the requirements of category 2.
Significance and advantages of division into zones
The division of potentially explosive areas into zones has proved successful. This division takes into account the different dangers posed by potentially explosive atmospheres and makes it possible to provide explosion protection that corresponds to circumstances both from a safety point of view and in terms of cost-effectiveness. The definition of the zones is consistently regulated for the European Union in Directive 1999/92/EG. It must be expertly applied to the actual conditions.
IEC 60079-10 assumes an almost identical division for gases and vapours, which also applies to future plants in line with USA Standard NEC 505. IEC 61241-10 supports zone division for dusts.
Potentially explosive areas are divided into zones according to the frequency and duration at which potentially explosive atmospheres occur.
This division gives the scope of the measures that need to be taken in accordance with Appendix II Section A of Directive 1999/92/EG in connection with Appendix I of Directive 94/9/EG.
