Effects of Venting Ducts

Usually the relief of explosions cannot readily, safely, or conventionally be released right at the source, whether in a building or in a working plant area. Therefore, these reliefs are directed to some discharge point where the 

Accordingly, to emphasize the safety problems affecting all industrial process plants and laboratories, the American Institute of Chemical Engineers established the industry-supported Design Institute for Emergency Relief Systems. The purposes of the Institute are [51]  

The research and technical evaluations have provided industry with extremely valuable information and design procedures, including, but not limited to, two-phase flow phenomena and runaway reactions during safety/over-pressure relief. 

Applied Process Design for Chemical and Petrochemical Plants 

Hazard Classes and Ks( Values for Selected Types of Dusts 

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Fig. 3. Design Chart to determine Effect of Vent Duct for Case Study 2 (Pstat = 1-1 bar abs, Kst = 150 bar m s", Straight Vent Duct) [9]...

G.A. Lunn, Guide to Dust Explosion Prevention and Protection, Part 3 - Venting of Weak Explosions and the Effect of Vent Ducts, Institution of Chemical Engineers, British Materials Handling Board, U.K., 1990. 

Figure 7-66. Increase in the reduced deflagration pressure for gases due to the effect of a vent duct. By permission, American Institute of Chemical Engineers, Meeting Mar. 6, 1988 by I. Swift (deceased) [56], with data from Ref. [54].

Vent ducts with a length of LD > LDS have no additional effect upon the pressure increase. Therefore, LDS will be the maximum vent duct length that has to be considered. The above-mentioned equation (23-18) is not valid for metal dusts. 

An explosion relief vent must be carefully sized to ensure that it will effectively relieve the potential explosion. Factors influencing the calculation include the material explosion pressure characteristics, the plant strength, vent position and the influence of ducting if required. Consideration must also be given to the plant configuration and the availability of an area into which the explosion can safely be discharged. 

The low level location should be well ventilated with the exhaust air directed to the same duct (plenum) where the lip vent exhaust, or the suction point adjacent to the cover of the enclosed machine, is directed. Excellent ventilation can be an effective method of keeping workers from being exposed to concentrations of solvent in excess of the posted (by a standard-setting authority or the manufacturer) exposure limit. But it raises the cost of solvent use. 

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