Explosion Suppression System

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. 

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-... 

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). 

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 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. 

Technical evaluation of options and consequence and risk analyses may be prepared. The analyses might include calculation of consequence severities for possible incidents. Subsequently, the basis for a mitigation system may be generated. This might involve, for example, a secondary containment structure, explosion suppression system, or scrubber. The rationale and technical design basis for such decisions should be documented and retained as part of the process knowledge. 

Fixed installations, such as water spray systems, halon systems, sprinkler systems, carbon dioxide extinguishing systems, explosion suppression systems, and other fire protection installations are often provided with flow and trouble detection switches connected to transmitters. A signal indicating the condition of the system should be sent to the attended location(s). 

Steam snuffing in solids dryers can also provide effective fire protection. In some cases, the major concern for a fired product dryer may be explosion involving product dust. Where there is a possibility of an internal dust explosion in a product dryer, a fast response explosion suppression system should be considered in addition to fire protection. 

Explosion Spectra and Spectrographic Measurements. See Vol 4, pp D548-R D549-L Explosion, Suppression System. Like any other protection system, an explosion suppression system is made up of three com-... 

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. 

The first step in the design of an explosion suppression system is to establish the propagation characteristics of the material in question. First, a sample of the fuel-air mixture is introduced into a cylindrical or spherical vessel, oxidation is initiated by the application of a spark, and the test data are recorded. For example, the radial flame velocity of H2 in air is 9 m/s (30 ft/s). 

The operation of an explosion suppression system is a race against time. On the one hand, there is the buildup in pressure due to the explosion, and on the other, the counterplay is the detection of the explosion, application of the suppressants to extinguish the deflagration, and corrective action to limit the extent of damage. The operation of a typical system is illustrated in Figure 3.58. 

Explosion suppression systems are and have been used in all parts of the world for some time, but these systems are usually protecting very small and unobstructed areas, where a mechanical pressure sensor can be used successfully to detect the initial pressure from an explosion. 

Now I will describe the U.S. Coast Guard test site and the explosion suppression systems used. The pump room measured 40 feet from the bilge level to the top hatch, and 32 feet from port side to starboard, and 16 feet from fore to aft. The total volume, including two first level wings, minus the space consumed by the pumps and other obstructions, was 18,000 cubic feet. 

Two explosion suppression systems were tested. They were based on the following principles ... 

Pressure sensors are not suitable as explosion suppression systems in large obstructed areas, but the basic ultraviolet (UV) detection system available today as a fire detector is capable of being used as an explosion detector, providing the exploding fireball is in the cone of vision of one of the detectors within the first 75 milliseconds. The extinguishing agent used must make... 

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