ANNEX IIESSENTIAL HEALTH AND SAFETY REQUIREMENTS RELATING TO THE DESIGN AND CONSTRUCTION OF EQUIPMENT AND PROTECTIVE SYSTEMS INTENDED FOR USE IN POTENTIALLY EXPLOSIVE ATMOSPHERES
3. Supplementary requirements in respect of protective systems
3.0. General requirements
3.0.1.Protective systems must be dimensioned in such a way as to reduce the effects of an explosion to a sufficient level of safety.
3.0.2.Protective systems must be designed and capable of being positioned in such a way that explosions are prevented from spreading through dangerous chain reactions or flashover and incipient explosions do not become detonations.
3.0.3.In the event of a power failure, protective systems must retain their capacity to function for a period sufficient to avoid a dangerous situation.
3.0.4.Protective systems must not fail due to outside interference.
3.1. Planning and design
3.1.1. Characteristics of materials
With regard to the characteristics of materials, the maximum pressure and temperature to be taken into consideration at the planning stage are the expected pressure during an explosion occurring under extreme operating conditions and the anticipated heating effect of the flame.
3.1.2.Protective systems designed to resist or contain explosions must be capable of withstanding the shock wave produced without losing system integrity.
3.1.3.Accessories connected to protective systems must be capable of withstanding the expected maximum explosion pressure without losing their capacity to function.
3.1.4.The reactions caused by pressure in peripheral equipment and connected pipe-work must be taken into consideration in the planning and design of protective systems.
3.1.5. Pressure-relief systems
If it is likely that stresses on protective systems will exceed their structural strength, provision must be made in the design for suitable pressure-relief devices which do not endanger persons in the vicinity.
3.1.6. Explosion suppression systems
Explosion suppression systems must be so planned and designed that they react to an incipient explosion at the earliest possible stage in the event of an incident and counteract it to best effect, with due regard to the maximum rate of pressure increase and the maximum explosion pressure.
3.1.7. Explosion decoupling systems
Decoupling systems intended to disconnect specific equipment as swiftly as possible in the event of incipient explosions by means of appropriate devices must be planned and designed so as to remain proof against the transmission of internal ignition and to retain their mechanical strength under operating conditions.
3.1.8.Protective systems must be capable of being integrated into a circuit with a suitable alarm threshold so that, if necessary, there is cessation of product feed and output and shutdown of equipment parts which can no longer function safely.