HEALTH & SAFETY
conventional vent for the same application. Great care on this point is required whenever considering replacement of a conventional vent with a flamefree vent. The weight and vent efficiency of flamefree vents are considered when selecting them for applications such as the protection of bucket elevators. The relevant codes are NFPA 61 - 2020 section 9.3.14 and NFPA 68 – 2018 section 8.8.
EXPLOSION SUPPRESSION Explosion suppression systems are designed to suppress a deflagration in its initial stage before destructive pressure can be generated. This is in contrast to explosion venting, which allows the deflagration to proceed to completion while exposing the equipment to combustion temperatures. Explosion suppression equipment is designed to respond in milliseconds to the signal generated by pressure or flame detectors monitoring the process. This results in explosion suppressors rapidly discharging a flame quenching agent, such as sodium bicarbonate, into the protected equipment volumes. This effectively halts the explosion in its infancy and results in a reduced explosion pressure that is safe for the protected equipment. “Think of explosion suppression as a fire extinguisher that triggers automatically but at about 1,000 times the speed,” says Nixon.
Suppression systems can be desirable, because the
speed of cleanup and refit allows for a quick return to production. With venting or flamefree venting, the explosion fully develops in the process equipment, requiring cleanup, mitigation of fire-related damage, and other consequences that take time to get the process back into operation. The suppression method of protection is often applied to double leg bucket elevators, used in grain handling. Protection consists of explosion detection and suppression of the elevator head and boot section, as well as explosion isolation of the leg casings, feed and discharge points, and dust extraction points. Suppression of single leg bucket elevators is also practical in grain applications, although the open internal volume between boot and head will require additional extinguishing agent injection points. Most importantly, whether applied to a double leg or single leg bucket elevator, suppression systems are recommended to incorporate explosion isolation to prevent the propagation of an explosion to connected equipment volumes such as silos.
EXPLOSION ISOLATION Explosion isolation is a vital component to any explosion protection strategy. The propagation of a dust explosion can result in secondary events in connected equipment which can be more destructive than the initial event. Isolation should be considered for all process interconnections such as inlet ducts,
discharge ducts, and dust extraction points. Although explosion isolation is a component of explosion suppression systems, it is not an intrinsic feature of explosion venting systems. When explosion vents are selected for explosion protection, a means of chemical or mechanical isolation must be considered to prevent explosion propagation to interconnected process volumes via inlet ducts, outlet ducts, conveyors, and dust extraction points. See NFPA 69 for compliant solutions and refer to NFPA 61-2020 section 9.7.4. While it can be tempting for the owner / operator to consider applying partial protection to a process system, care must be taken to manage the risk both from and to connected equipment. A piece of unprotected equipment can be the Achilles heel to a facility protection plan. For grain and food processors, there are many critical decisions involved beyond the DHA in selecting dust explosion prevention, protection, and mitigation equipment given the areas at risk, the methods of protection, relevant NFPA codes, other jurisdictional requirements, and the type of material processed. However, careful attention to dust explosion mitigation and isolation in processing equipment can ensure the protection of both facility personnel and infrastructure. This will also limit the potential for preventable production and business interruptions.
BS&B Safety Systems
www.bsbsystems.com
YOUR WORKSHOP Change the game
An extremely durable and reliable
storage solution perfect for industrial and retail environments.
UP
with the BiG340 shelving from BiGDUG.
FACTORY&HANDLINGSOLUTIONS | APRIL 2023 17
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44
