Common Sense Solutions for Explosion Protection

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Posted in: , on 31. Mar. 2003 - 07:58

We are a manufacturer of explosion vents and doors, as well as some related equipment such as dampers and line blinds. We would be pleased to assist any readers wherever we can.

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Explosion Protection For Pulverizing System

Posted on 23. Jun. 2003 - 04:18

NFPA standards say that an explosion involving the process of grinding or pulverizing aluminum can be expected to occur. The pressures generated during a dust explosion can be tremendous. I am aware of what NFPA recommends in the way of explosion protection. What is the standard practice used in the aluminum pulverizing industry for fire/explosion protection on the grinders, ducts, mill fans, dust collectors, etc..?

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Re: Common Sense Solutions For Explosion Protection

Posted on 23. Jun. 2003 - 08:33

Aluminum dust is extremely nasty being in the highest of the explosibility Class and capable of generating 180 psig explosive pressures. I don’t think I can speak to what the industry in general does (better someone from a processor does this), but can say that many companies have great difficulty in addressing this with aluminum (or magnesium as we have also had occasion to work with). In my opinion, explosion suppression is not appropriate for such a service due to reaction times. So, typically one needs to put the dust collector outdoors, equip it with explosion vents keeping in mind the “zone of influence” and to isolate it mechanically with explosion isolation valves available in our industry (including our own) incorporate heavy duty knife gate style valves that mate with a round duct flange. The isolation gate has to be capable of taking both the pressure and the shock load and have electronic circuitry that transmits on an ultra fast basis. Given duct velocities, the likely source of ignition and the foregoing a sufficient sensing distance upstream to get the gate closed. Detection methods include pressure and infra red sensing being the most likely followed by heat. Obviously, fan shutdown (dependent on location etc.) may have to be incorporated. And you don't want the isolation valve to be the only thing to survive the explosion! So you have to have a very rugged construction of your system. As to the equipment inside the plant, wherever explosion venting can be utilized premised on discharge ducting routing everything to a safe zone outdoors, I would recommend as the best approach – this means such equipment must be kept close to an appropriate outside wall or close to access through the roof (though the latter is not desirable given a choice). Of course, proper grounding is a must as is the use of spark-proof fans, motors etc. Please note that the products of discharge from an aluminum dust explosion can be particularly hazardous (especially to personnel) as there can be molten globs of aluminum spraying everywhere.

I hope that this is of some assistance.