From our friends at Powder & Bulk Solids "Ask The Experts Blog", an article by Dr. Mayer with Rembe answering the question about what the requirements are for old dust collectors:
Explosion Venting/Suppression Q&A
Answered September 9th, 2010 by Expert:Not necessarily. You really have a number of options. Depending on distances, Preds and such, you might be able to duct and vent the collector to the outside with an explosion panel if your collector is close to an exterior wall. But you need to pay attention to the Pred of the collector and you may need to strengthen your collector (you mention it is old!) due to potential back pressure that will build up. Another option is to safely vent your dust collector with a flameless vent, designed to capture both the flame and pressure of a combustible dust explosion, should one occur. Or, as you mentioned, you might decide you want to move the dust collector outside to a “safe” location, away from the facility and away from areas where people might walk or gather or vehicles might park or be located.
This is a good answer by Dr. Mayer. Things that need to be considered are the size of the dust collector, age, strength, location, and proximity to an outside wall. To meet current NFPA 654 Standards you will also need to consider not only explosion venting, but also sprinkler or deluge, a Spark Detection System, Isolation, and if the collector is returning air back to the plant, you may also need to consider Spark Detection and an Abort Gate. If you have questions in this area, we can help.