4.) Determine if there is a combustible dust issue and what types of explosion protection technologies to apply.
The first step in this process is to determine whether the process dust is combustible. It is important to know that under the latest NFPA standards, any dust above 0 Kst is now considered to be explosive, and the majority of pharmaceutical dusts fall into this category. The only way to be sure is to commission explosion testing available from many commercial test laboratories. If an initial basic test on the dust sample is positive, then the explosive index (Kst) and the maximum pressure rise (Pmax) of the dust should be determined by ASTM E 1226-12a, Standard Test Method for Explosibility of Dust Clouds.
A dust collection equipment supplier experienced in combustible dust issues can use these values to apply the relevant NFPA standards and to correctly select and size explosion protection equipment. The relevant standards for pharmaceutical professionals include NFPA 654 – Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing and Handling of Combustible Particulate Solids; NFPA 68 – Standard on Explosion Protection by Deflagration Venting; and NFPA 69 – Standard on Explosion Prevention Systems.
The devices and systems used for compliance fall into two general categories: passive and active. The goal of a passive system is to control an explosion to keep operators safe and minimize equipment damage. One of the most cost-effective – and therefore widely used – passive devices is the explosion vent, which is designed to open when predetermined pressures are reached inside the collector.
An active system, by contrast, actually prevents an explosion from occurring. It may be the system of choice if the collector is located inside the manufacturing facility or if the unit is collecting hazardous or potent material that cannot be released directly to the outside environment. An active system involves much more costly technology and typically requires re-certification every three months.
One example is a chemical isolation system, which can be installed in inlet and/or outlet ducting. It reacts within milliseconds of detecting an explosion, creating a chemical barrier that suppresses the explosion within the ducting. A chemical suppression system is similar in concept, except it is designed to protect the dust collector itself as opposed to the ducting. Sometimes used in tandem with isolation, a chemical suppression system detects an explosion hazard and releases a chemical agent to extinguish the flame before an explosion can occur.
5.) Consider the functional acceptability of the equipment.
Even if it’s determined that a dust collection system will meet applicable emission and combustible dust standards, it is still not a good choice if it performs unreliably or if it is prohibitively costly to install, operate and maintain. So the final step in the selection process is to make sure the system is designed for optimum functionality.
Where will the dust collector be located? If possible, locate the dust collector either outdoors or in an indoor maintenance or mechanical area adjacent to the Good Manufacturing Practice (GMP) space. Either way, you will need to establish the best overall installation scheme and the best way to run ducting to the outdoor location or adjacent room, taking explosion isolation devices into consideration as required.
If it is necessary to locate the dust collector within the GMP space, compliance with FDA requirements will impose tight controls on the collector as with all equipment within the processing area. If a combustible dust is involved, chemical suppression and isolation will usually be the default technologies, and these are typically the most costly methods for explosion protection.
Is it designed for energy-efficient performance? This will depend on a variety of factors, including the sizing of the equipment, air-to-cloth ratio and type of filters used. Also, the use of a variable frequency drive (VFD) can help control dust collector fan speed. This electrical control method is highly efficient in maintaining desired airflow/static pressure, while greatly decreasing energy consumption.
What will be the Total Cost of Ownership (TCO)? Though the initial cost of the system is important to know, life-cycle cost (also known as TCO) is far more significant. There are three main components of TCO: energy, consumables, and maintenance and disposal. Your equipment supplier should be able to generate a worksheet that predicts the TCO over time for the proposed dust collection system. This mathematical calculation can be used to compare the cost of two or three different filter types to determine which one is best for the application. For example, a premium filter may carry a higher initial cost but will save money over time through longer service life, reduced change-out and disposal costs, and lower average pressure drop resulting in reduced energy consumption.
Published in the December 2013 edition of Pharmaceutical Manufacturing magazine
David Steil is pharmaceutical market manager at Camfil Air Pollution Control (APC), where his responsibilities include global sales and marketing to the pharmaceutical/nutraceutical industries. He previously spent 12 years with a major pharmaceutical company in the corporate Environment, Health and Safety group. Steil is a member of the International Society for Pharmaceutical Engineering (ISPE) and the American Industrial Hygiene Association (AIHA).