Retrofitting Explosion Protection

RETROFITTING EXPLOSION PROTECTION

Explosion protection is still as much an art as it is a science and the scientifically developed technical principles that are available, are slow to find their way into everyday engineering at all but some large corporate engineering departments. Given that, when faced with the need to protect existing equipment/systems one faces even more obstacles and risk management decisions than is experienced with new projects. The need to retrofit can be driven by a number of factors:

products being handled having been found to have the capacity to explode, previously unknown
changes in processing that results in smaller particle size, higher concentrations, or additional components that have increased volatility;
an incident that heightens awareness;
intervention of regulatory authorities or the facility's insurance underwriter.

Once the need is established, there are a number of preliminary steps that should be taken all based on a recognition that it is totally irrational to isolate a given piece of equipment from the system in which it is going to operate when assessing explosion protection needs. Given that, there is always a need for a HAZOP (Hazard & Operability) review to assess the areas of risk; to rank their seriousness and likelihood; to establish potential causes and how often they may occur; to assess their impact in damages, potential for personnel injury, lost production etc.; and to assign levels of acceptability of risk to the various hazards identified. Then identify solutions for each of the hazards identified as being outside the range of acceptability. As an example from an explosion protection perspective, things may start out with a new recognition of the need to protect a dust collector due to a fire and low level explosion for some strange reason, having had a small fire, one would never say we've experienced a fire and the results were not that dramatic, so we can deal with a fire and yet one hears that too often when it comes to a low energy explosion as though it were indicative of what is rational to expect as worst case for future incidents.

The next step is to establish the basis on which the explosion protection design scenario is to be founded and to what authorities is the end user answerable to. In respect to design, the National Fire Protection Association (NFPA) has various design Guidelines that may apply including but not limited to: NFPA68 Guide for Venting of Deflagrations; NFPA61 Prevention of Fires and Explosion in Agricultural & Food Processing Facilities; NFPA484Combustible Metals, Metal Powders, and Metal Dusts; NFPA664 Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities and the European Guideline VDI 3673 Pressure venting of dust explosions. The Authorities will vary from one jurisdiction to another and one country to another, but will generally include: the Insurance Underwriter, the Fire Marshall, the Building Department, the Department of Labor, the plant's Health & Safety Committee among others.

So, now one has established the foregoing, and wants to move on to design anticipating some of the common hurdles. First is the fact that the equipment/system to be protected is usually found to be indoors (where in a new design knowing of explosion hazards, all or part of it would be located outdoors) which escalates the expense of protection because discharge ducting to an outside wall/roof (an expense in itself and impractical beyond 10 foot runs – typically irrational beyond 20 feet) is going to require larger relief areas owing to induced backpressures to the venting process. That is given the understanding that the Technology of Protection can range in price dramatically but where the type of device is rational to use, would typically be from least to most expensive solutions: explosion doors and vents (dependent on quantities and common denominators, either may end up the wise price choice); inerting: explosion suppression; isolation – or combinations of same. Further, venting through the roof means dealing with ice & snow loads in some climates and obstruction of roof access by process piping, wiring, overhead cranes etc. further complicate things.