Contained dust collection equipment is used in pharmaceutical facilities for a variety of reasons, from environmental compliance and employee health and safety to preventing cross-contamination of materials in multi-product manufacturing facilities.
Given these concerns, and the fact that many pharmaceutical dusts are potent and/or hazardous, contained dust collection systems are found in the majority of pharmaceutical processing facilities today. Such systems typically use safe-change containment for both the filter cartridges (bag-in/bag-out) and the discharge system underneath the collector (continuous liner technology).
By David Steil, pharmaceutical market manager, Camfil Air Pollution Control
Following are five important tips for designing and selecting a contained dust collection system — pointers that should give pharmaceutical professionals a general overview of the process to make sure all their bases are covered when approaching dust collection system design.
1 — Conduct a risk assessment to identify and prioritize goals.
The dust collector must o en satisfy many masters with varied agendas. The NFPA is concerned with explosion protection; the FDA with delivering safe products to consumers; OSHA with indoor environmental and safety issues; and the EPA with outdoor air quality. Pharmaceutical facility managers are tasked with satisfying all these entities while also meeting internal goals of product quality, operational efficiency and cost control.
What are the expectations for the dust collection system? A risk assessment is needed to help identify safety and performance goals for the dust collector and how to achieve them. It is best to involve a professional engineer who can commission appropriate explosibility and bench testing to determine other properties and characteristics of the dust, as well as surrogate testing as appropriate to determine appropriate system design.
2 — Consider surrogate testing.
Used as part of the risk assessment, surrogate testing can provide useful performance information prior to installation to help determine if the planned dust collection system will meet environmental and safety goals. Surrogate testing involves the use of a substitute or surrogate compound to simulate an API and predict real world performance. Test conditions should mimic workplace operations as closely as possible without incurring the expense or health concerns of handling the API.
In a typical test, the surrogate dust is fed to the collection system on a pre-determined schedule. Operators equipped with air sampling devices perform bag-in/bag-out filter change-outs and contained discharge system clean-outs under conditions that simulate shift-equivalent operations. A combination of air, surface wipe and personal samples are taken at specified intervals during the test period to evaluate performance.
If samples are found to be below established thresholds, the manufacturer will accept the surrogate test as evidence that the contained dust collection system as designed can be expected to provide the required level of emission control performance under real world operating conditions. By validating equipment performance during the engineering phases, it is thereby possible to reduce costs while ensuring proper equipment design and selection.
3 — Incorporate a Risk-MaPP approach to cross-contamination control.
There are several ways that cross-contamination occurs. These include airborne transfer, the airborne migration of particulate contaminants from one manufacturing space to another; and mechanical transfer, which occurs when particulate is carried from one processing area to another on the shoes or clothing of operators and/or via equipment that is operated in more than one location. A contained dust collector can address both problems by capturing airborne particles while simultaneously minimizing the build-up of surface dust that can be transferred mechanically from one place to another.
How does a facility ensure that Product A is not contaminating Product B? Sampling is critical and should include both surface sampling and airborne concentrations. Surrogate testing and sampling are addressed in section 2 above, but with a focus on environment, health and safety. When we look at cross-contamination testing, the methodology is similar but the end goal is product quality rather than operator safety. It is important not to confuse the two: i.e., be cautious about using industrial hygiene data for cross-contamination purposes. The two goals are different, and the quality thresholds of one program may be more — or less — strict than the other.
Surrogate testing can help with quality control programs by providing real-world test results to the FDA that indicate how the planned engineering controls will be expected to perform. Testing and sampling can also help pharmaceutical manufacturers to identify the most cost-efficient equipment for a given application. Some engineering controls relating to dust collection can add significant cost to a project. There is a balancing act between what will work and what will be economically feasible, and a scientific test-based approach will be far more accurate than guesswork in striking the right balance.
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 recertification 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. A thorough implementation review should include seeking answers to the following questions:
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, lifecycle 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.
This article was featured in the December 2013 issue of Pharmaceutical Manufacturing Magazine.
