Explosion suppression

The explosion suppression system can be regular or ultra-high-speed deluge (UHSD) systems, and their suppressant velocities of 60-90 m/s (200-300 ft/s) must exceed the radial flame velocities, which range from 0.6 to 24 m/s (2 to 80 ft/s). The response times of explosion suppression systems for the detection are about 25 ms, and the suppressant becomes effective in about 50 ms. In the case of deluge systems, water is applied in about 100 ms from the time of activation. 

Renewable energy processes include the operation of combustion and H2-handling systems and therefore have to be protected against fires (see Section 3.8) and explosions. Because chemicals display different explosive characteristics and processes differ in physical dimensions, an explosion suppression system is usually a design package. In many instances, approval for insurance must be obtained from fire underwriters with evidence of design capability demonstrated in a test. 

Explosion suppression and ultra-high-speed deluge systems (UHSD) act within milliseconds to extinguish an explosion or fire almost at its inception. The two techniques are quite different. Explosion suppression systems are designed to (1) confine and inhibit a primary explosion, (2) prevent a secondary and more serious deflagration or a detonation, and (3) keep equipment damage at a minimum. 

Burning—the flame does not spread or diffuse but remains at an interface where fuel and oxidant are supplied. 

Deflagration or explosion—the flame front advances through a gaseous mixture at subsonic speeds. 

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Explosion Suppression With explosion suppression, an incipient explosion is detected and—within a few milhseconds—a suppressant is discharged into the exploding medium to stop combustion. Pressure and optical detection systems are used suppressors are pressurized and release the suppressants when actuated by an electroexplosive device. 

Deflagration pressure can be reduced substantially by suppression. Figure 26-30 shows the pressures measured in an ethylene-air explosion and a sodium bicarbonate-suppressed ethylene-air explosion. Fike Corporation, Blue Springs Missouri, and Fenwal Safety Systems, Marlborough, Mass., supply explosion suppression systems. 

Capable of withstanding an explosion overpressure reduced by explosion suppression or explosion venting... 

Explosion-Pressure-Resistant Design for Reduced Maximum Explosion Overpressure with Explosion Suppression Explosion suppression systems provide one means to prevent the buildup of an inadmissibly high pressure, which is the consequence of explosions of combustible material in vessels. They operate by effectively extinguishing explosion flames in the initial stage of the explosion. An explosion of combustible material can generally be regarded as successfully suppressed when the maximum explosion overpressure can be lowered to a reduced explosion overpressure of not more than 1 bar (see Fig. 26-40). 

Depending upon the design criteria of the installed suppression system, an unsuppressed explosion overpressure of around 7 to 10 bar is reduced to a suppressed reduced explosion overpressure which lies in the range of Fred,max = 0-2 to 1 bar. Thus, vessels need to be explosion resistant for an overpressure of maximum 1 bar (ISO Standard 6184/4, Explosion Protection Systems Paii 4 Determination of Efficacy of Explosion Suppression Systems, Geneva, 1985). 

The best advantages of explosion suppression systems is that they can also be used for explosions of combustible materials with toxic properties and that there is no penetration on the location of the process equipment for safe application. 

Explosion suppression systems comprise explosion detec tors, pres-... 

The most widely deployed industrial explosion suppressant is mono-ammonium phosphate powder (MAP). This suppressant has a wide range of effectiveness. However, it can prove to be a contaminant, necessitating stringent clean-down procedures after a suppressed explosion incident. This limitation is overcome by selecting a sodium... 

A suitable locldug mechanism must ensure that the production plant can be started up again only if the explosion suppression svstem is fiilly operational. The alarm center must be designed so that, if work is performed within the protected vessel, the detectors can be made inoperable and secured against inadvertent triggering. 

Design of explosion suppression systems is clearly complex, since the effectiveness of an explosion suppression system is dependent on a large number of parameters. One Hypothesis of suppression system design identifies a limiting combustion wave adiabatic flame temperature, below which combustion reactions are not sustained. Suppression is thus attained, provided that sufficient thermal quenching results in depression of the combustion wave temperature below this critical value. This hypothesis identifies the need to deliver greater than a critical mass of suppressant into the enveloping fireball to effect suppression (see Fig. 26-43). 

Volume of vessel (free volume V) Shape of vessel (area and aspect ratio) Type of dust cloud distribution (ISO method/pneumatic-loading method) Dust explosihility characteristics Maximum explosion overpressure P ax Maximum explosion constant K ax Minimum ignition temperature MIT Type of explosion suppressant and its suppression efficiency Type of HRD suppressors number and free volume of HRD suppressors and the outlet diameter and valve opening time Suppressant charge and propelling agent pressure Fittings elbow and/or stub pipe and type of nozzle Type of explosion detector(s) dynamic or threshold pressure, UV or IR radiation, effective system activation overpressure Hardware deployment location of HRD suppressor(s) on vessel... 

The combination of explosion safety technologies can provide more effective safety than is possible by deploying just one safety measure. In this respect, the improved capabilities of explosion suppression further enhance overall explosion protection capabihty. 

Comparison of E] q)losion Protection Design Measures In Table 26-24, comparison is made of the explosion protection design measures of containment, explosion venting, and explosion suppression. Regarding the effectiveness of the different explosion design measures, all three techniques are equal if the design of these measures is performed properly. 

The loss of material hy using containment and explosion venting is always much greater than that hy using explosion suppression. 

See ignition Oxygen monitored inerting system sources, all these, Explosion suppression devices can lead to fire or explosion. ... 

Protective features Provide protective as well as control features, e.g. pressure and vacuum relief, explosion suppression relief, advance inerting, containment... 

The limiteit access to the containment building either to facilitate isolation or for vapor or hydrogen explosion suppression makes it desirable to locate as much equipment outside of containment as possible. 

Figure 7-62. Typical Fenwal explosion suppression system. By permission, Fenwal Safety Systems, Inc.

Table 7-31 lists the explosibility index that is a relative measure of the potential damage from a dust explosion. A rating of 2 to 4 requires large vent areas. Above 4, for most cases, the explosion cannot be controlled by venting design and therefore requires the use of protection such as inert gas or explosive suppression systems, some of which are commercially available. 

Explosion calculations, 499-504 Estimating destruction, 501 Overpressure, 502 Pressure piling, 501, 504 Relief sizing, 505 Scaled distance, 502, 503 Schock from velocity, 503 TNT equivalent, 499-504 Explosion characteristics of dusts, 515 Explosion suppression, 518 Explosion venting, gases/vapors, 504 Bleves, 504 Explosions, 482 Blast pressure. 496 Combustion, 482 Confined, 482 Damage, 498-501 Deflagration, 482 Detonation, 483... 

Nuclear installations are provided with a pressure explosion suppression and containment shell as an accommodation system against any sudden energy release resulting from an uncontrolled nuclear fission reaction. The internal air pressure is maintained at a level lower than the external atmosphere. 

The maximum rate of pressure increase indicates the robustness of an explosion. Thus the explosive behavior of different materials can be compared on a relative basis. The maximum rate is also used to design a vent for relieving a vessel during an explosion before the pressure ruptures the vessel or to establish the time interval for adding an explosion suppressant (water, carbon dioxide, or Halon) to stop the combustion process. 

Explosion suppression During a suppression of an explosion, not products, residues from combustion, residues from gases, or flames can escape from the protected vessel, because an explosion suppression system reduces the effects of these explosions to a harmless levef, by restricting the action of the flames during the initial phase of the explosion. This prevents the installation in question from being destroyed and people standing in the area of the installation from being injured. A further benefit of explosion suppression systems is that they can be deployed for combustible products with toxic properties and can be used irrespective of the equipment location. 

An explosion can generally be considered suppressed if the expected maximum explosion pressure Pmax at the optimum concentration of the combustible product (7 to 10 bar)—assuming the explosion suppression system has an activation overpressure P of 0.1 bar—is reduced to a maximum reduced explosion overpressure Pled.ma< < 1 bar. This means that a vessel safeguarded in this way needs to be designed so that it is secured against explosions of up to 1 bar (equivalent to P .d ln, ). The activation overpressure P is that pressure at which an explosion suppression system will be activated. 

To initiate an explosion suppression system, a detector is used to sense either an overpressure generated by, or a flame of, an incipient explosion. It is important to locate the detector in a position that ensures sufficient time for the suppression system to sense and activate the devices to extinguish the explosion. 

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