Explosion protective measures

Proper installation is dependent on the existing explosion protection measures and on the corresponding isolation system to be used. This guarantees operability. In addition the application and installation remarks of the manufacturer as well as the limits of application in accordance with the Type-Examination Certificate are to be obeyed in every detail. In Table 23-15 the most frequently used isolation systems for explosion protection measures are summarized. 

TABLE 23-15 Most Frequently Used Isolation Systems as Related to the Installed Construction Explosion Protection Measure... 

Industrial fire protection and safety engineers attempt to eliminate hazards at their source or to reduce their intensity with protective systems. Hazard elimination may typically require the use of alternative and less toxic materials, changes in the process, spacing or guarding, improved ventilation or, spill control or inventory reduction measures, fire and explosion protective measures - both active and passive mechanisms, protective clothing, etc. The level or protection is dependent on the risk prevalent at the facility versus the cost to implement safety measures. 

Human factors and ergonomics concern the ability of personnel to perform their job functions within the physical and mental capabilities or limitations of a human being. Human beings have certain tolerances and personal attitudes. Tolerances can be related to the ability to accept information, how quickly the information can be understood and the ability and speed to perform manual activities. When information is confusing, lacking or overtaxing, the ability to understand and act upon it quickly or effectively is absent. It is therefore imperative to provide concise, adequate and only pertinent information to do all the tasks associated with petroleum activities. This includes activities associated with emergency fire and explosion protection measures. 

The maximum explosion pressure and maximum rate of pressure rise values are determined by using the 20 L sphere apparatus. The dust sample is dispersed within the sphere, ignited by chemical igniters, and the pressure of the resulting explosion is measured. The sample size is varied to determine the optimal dust cloud concentration. The maximum pressure and rate of pressure rise are measured and used to calculate the explosion severity (Kst) value of the dust cloud. These data can be used for the purpose of designing dust explosion protection measures. 

If evolution or formation of an explosible atmosphere cannot be prevented and all sources of ignition cannot be reasonably eliminated or excluded, then the possibility of a dust cloud explosion persists. Under such conditions, explosion protection measures should be taken to protect people and minimize damage to the plant. It should be noted that explosion protection measures should be considered in addition to taking all reasonable steps to reduce the possibility of formation/spread of dust clouds and exclude potential ignition sources. Explosion protection measures include the following. 

Regardless of what type of explosion protection measure is considered, the dust cloud explosion should be prevented from propagating from the location where it originates to other locations in the plant. This is referred to as explosion isolation. Dust explosions can propagate through pipes, chutes, conveyors, etc. The first step in isolating an explosion is to avoid unnecessary connections. If this is not possible, barriers should be created in the path of the explosion. 

Taking measures to protect against the consequences of potential dust cloud explosions. Explosion protection measures include ... 

The assessment of an explosion hazard has to include the close vicinity of the installation or functional unit. In the case of in-house installations the complete room has to be considered. If an existing plant is evaluated, explosion protection measures already installed may not be accounted for in this analysis of an explosion hazard. If they were selected adequately in former times, then the result of the study will reconfirm their necessity. 

The chosen explosion protective measures must also remain effective during startup and shutdown of the plant, as well as during disturbances. If this goal can not be achieved by these preventive measures, then constructive measures are used, for example ... 

Explosion protection measures expect the explosion to take its course, but ensure that it does so safely without any effects on the personnel and equipment. The three possible ways of protection from a hre or explosion are (1) venting (2) containing and (3) suppressing. 

Which explosion protection measures are appropriate or necessary at a specific place depends on the prevailing hazards. In case of a commercial facility subject to explosion risks the employer is obliged to indicate so-called explosion protection zones . The zone a place belongs to depends on the frequency or probability an explosive gas mixture is to be expected in dangerous quantities during normal operation. The zones are ... 

Analogous zones 20-22 exist for the occurrence of explosive dusts.) A place where the occurrence of a dangerous gas mixture is not to be expected normally at all belongs to neither of the zones. No special explosion protection measures are necessary at such a place. 

The criticality of the equipment to continued business operations. Possible fire and explosion exposures to the facility from adjacent hazards. The effectiveness of fire and explosion protective measures, both active and passive. 

Facilities that are deemed critical or highly manned should be relocated out of the overpressure circles or provided with explosion protection measures. Other systems within these overpressure zones should be evaluated for the specific benefits of providing explosive protective design arrangements. An example is provided in Figure 16.1. 

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