How to Predict Contained Dust Collection System Performance

Oct. 1, 2014
Surrogate testing offers a way to provide meaningful performance information prior to installation

The proper selection and operation of contained dust collection equipment is critical to the operations in pharmaceutical plants for a host of reasons, from environmental requirements and employee health and safety, to production cleanliness and efficiency. Historically, no performance data has existed on contained dust collection systems until they were already installed.

Surrogate testing offers a way to provide meaningful performance information prior to installation, to help pharmaceutical manufacturers determine if the equipment will meet required specifications and standards for a specific project. It can thereby help to reduce costs while also reducing risk. 

Dust collection equipment used in the surrogate test.

In selecting dust-collection equipment for pharmaceutical applications, it is critical to understand the potent, toxic or allergenic properties of the dust. This information helps determine the Occupational Exposure Limit (OEL), a value specific to each individual API. The OEL is defined as the amount of material determined to be the maximum air concentration, expressed as a time weighted average (TWA), to which a healthy worker can be safely exposed for an eight-hour shift, 40-hour work week. This value is typically expressed in micrograms per cubic meter of air (µg/m3).

In most cases, some level of isolation and containment is required due to the fact that the pharmaceutical dust is hazardous and cannot be released into the surrounding environment for employee health and cross-contamination concerns.

The equipment selected for evaluation in this test was a cartridge-type contained system designed for high efficiency collection of dry dusts. It contained four cartridge filters rated at 99.999 percent efficiency (MERV 16) on 0.5 micron particles and larger. The supplier’s stated claim was that the equipment would perform at or below the standard threshold limit of 1.0 µg/m3 for an 8-hour TWA.

The dust collector was equipped with soft-walled, safe-change containment technology for both the filter cartridges inside the collector and the discharge system underneath. The filter cartridges utilized bag-in bag-out (BIBO) technology, with two cartridges removed per bag. The discharge system utilized continuous liner technology to contain the dust that would be released from the cartridges to the hopper below during automatic reverse pulse-cleaning.

To perform the testing, the dust collection equipment supplier engaged an independent laboratory accredited by the American Industrial Hygiene Association (AIHA). Together the supplier and laboratory outlined a test protocol conforming to the ISPE Good Practice Guide, “Assessing the Particulate Containment Performance of Pharmaceutical Equipment.”

Operators each wearing single and multi-event air sampling pumps and filters (indicated by yellow circles) before the liner change operation.

To supplement the ISPE guidelines, the test protocol also incorporated AIHA Good Industrial Hygiene Practices. The methodology included the following elements: 

Surrogate compound selection: Lactose was selected as the compound that would best simulate the customer’s API without posing a hazard to the operators or the surrounding environment. The surrogate dust was 100 percent lactose, undiluted with other materials. In real-world processes, the API is incorporated in a specified concentration and mixed with other inactive substances and excipients. By the time it reaches the dust collector, the API might account for just a very small percentage of the dust being captured. By using an undiluted test dust, the collector would thereby be challenged with a “worst case scenario.”

Test room: The dust-collection equipment was located in a dedicated and decontaminated area of the equipment supplier’s factory. The test area was isolated, sealed off, pressure-washed and cleaned prior to the test. Access was tightly controlled to keep the area pristine and avoid contamination. Humidity, temperature and pressure were all tightly maintained, with an air change rate of 3-5 changes per hour prior to the test.

The test conditions mimicked workplace operations as closely as possible. Working from a charging area adjacent to the test room, an employee charged the lactose surrogate dust to the collection system on a pre-determined schedule. Two charge and discharge cycles using 12.5 kg of lactose per cycle occurred during the first simulated work-shift test day, and one additional charge of 12.5 kg also occurred on this day. This third charge of lactose was left in the dust collector until the following test day.

Test operators conducted an additional liner change operation on the following day to discharge the third charge of 12.5 kg of lactose left in the system the previous day. They performed two additional charges of 12.5 kg of lactose to the system to conduct liner discharges No. 2 and 3. The recirculating air-conditioning system in the test room was kept off so as not to skew results during the test.

Background air and swab samples were collected after the initial cleaning of the test location. The purpose was to determine the validity of the air and swab samples collected during the surrogate test. If the background sample results showed a high level of contamination, then the results of the surrogate test would be skewed and inaccurate.

Personal air samples were collected on ultra high efficiency glass fiber filters enclosed in cassettes using air pumps designed to draw a measured volume of air at a steady flow rate through the cassettes. Pumps were calibrated on-site before and after each sample period. The two test operators wore sampling pumps and filters attached in the breathing zone. Each operator wore two sampling pumps and filters — a “single event” unit to monitor specific short-term events of 15-20 minutes’ duration; and a “multi event” unit to monitor total exposure for the duration of the test, covering a time period equivalent to a standard employee work shift. Since a real-world employee may perform many different tasks over the course of a shift, it is important to do both types of sampling to monitor possible spikes in exposure levels, pinpoint problem areas, and receive an accurate picture of dust collector performance.

The testing equipment thereby simulated the respiratory rate of a human being; and the material collected on the filter media over time provided a snapshot into potential operator exposure to the surrogate under real-world conditions.

Operators performing BIBO filter cartridge change.

General area testing. Sampling pumps with air filters in cassettes as described above were also used for non-operator monitoring. General area event air samples were collected at specified equipment locations during the discharge cycles and filter changes to monitor surrogate emission levels associated with those tasks. In addition, two air sampling pumps with filters were located in opposite corners of the test room. These pumps ran throughout the entire testing event for general area background evaluation in the test room. The purpose of this additional sampling was to identify and measure whether any test dust was escaping into the ambient air or migrating to other areas of the test room.

Swab sampling or surface monitoring provided a supplemental measurement technique. Swab sampling is typically used to assess the amounts of surrogate contamination on a surface. It is regarded as a subjective test and is not a standardized technique for establishing health risks; however, it is an important measure in establishing the containment performance of the equipment. Swab samples were taken in several locations — including background general area samples taken prior to testing, and samples collected at specified equipment locations after the discharge cycles, and after the second and fourth filter change tasks.

Field blank samples. As a quality control procedure, a blank air sampling filter and surface swab were provided to the laboratory for analysis. These “field blanks” — unused and unidentified samples submitted at the same time as the actual samples — helped to provide a quality control check to verify accuracy of the lab work. 

The two operators performed BIBO filter cartridge changes, manipulating a total of 16 cartridges during the test period: eight cartridges saturated with lactose and eight new cartridges replaced into the system. To perform filter change-out, the operators opened the access door and worked through the bags to accomplish safe change-out while avoiding direct exposure to the contaminated filters, removing the used cartridges and then installing the new ones. The operation was completed four times to simulate shift equivalence (206 minutes total).

Continuous liner discharge operation.

During operation in the test period, the dust collector’s cleaning system periodically sent reverse air pulses to the filter cartridges to blow material off the filter media. This pulse-cleaning action caused dust to accumulate in the hopper at the base of the collector to simulate real world conditions. To release this material, the operators performed the “continuous liner discharge operation” to collect the material in a safe manner for disposal. They performed three discharge operations and one liner replacement to simulate shift equivalence (126 minutes). 

In the sampling performed prior to the test, a background surface lactose concentration of 0.39 micrograms was detected on the test room floor. The results for the remaining three background surface swab samples were below the 0.025 μg limit of quantification. The results of the two background general area air samples collected before the test were also below the limit of quantification, resulting in reported airborne concentrations of less than 0.018 micrograms per cubic meter (μg/m3). Of the 47 samples taken during the operational test, all were below the established OEL of 1.0 μg/m3, and many of these were significantly below the established threshold. Focusing on the personal air sampling results, which are significant in that they simulate real-world operator exposure, the following measurements can be noted:

BIBO filter change-out:
• Multi-event sampling from the breathing zone of Operator 1 yielded an airborne lactose concentration of 0.38 µg/m3 (206 min).
• The multi-event sampling from the breathing zone of Operator 2 showed a concentration of 0.19 µg/m3 (206 min).
• Single-event samples from the breathing zone of Operator 1 ranged from 0.14 µg/m3 to 0.64 µg/m3 (36 to 47 min).
• Single-event samples from the breathing zone of Operator 2 ranged from < 0.048 µg/m3 to 0.40 µg/m3 (36 to 47 min).

CLD operations:
• Multi-event sampling from the breathing zone of Operator 1 showed an airborne concentration of 0.077 µg/m3 (126 min).
• Multi-event sampling from the breathing zone of Operator 2 showed a concentration of 0.045 µg/m3 (126 min).
• Single-event samples from the breathing zone of Operator 1 ranged from <0.083 µg/m3 to < 0.25 µg/m3 (8 to 24 min).
• Single-event samples from the breathing zone of Operator 2 ranged from nearly identical, ranging from < 0.084 µg/m3 to < 0.25µg/m3 (8 to 24 min).

Based on these results, the customer accepted the surrogate test as evidence that the contained dust-collection system as designed could be expected to provide the required level of emission control performance under real-world operating conditions. By validating equipment performance during the engineering phases of the project, they were able to reduce potential equipment modification costs while also reducing risk.

It is important to note that dust-collection equipment must also be evaluated for ease of service and operation, energy usage, reliability, return on investment and total cost of ownership. Viewed in this context, a well-designed surrogate test program is an important tool for the pharmaceutical industry in the overall evaluation, verification and purchasing process for this type of equipment.

David Steil is pharmaceutical market manager at Camfil Air Pollution Control (APC). He previously spent 12 years with a major pharmaceutical company in the corporate Environment, Health and Safety group.

International Society for Pharmaceutical Engineering, Assessing the Particulate Containment Performance of Pharmaceutical Equipment, 2005, pages 5-78.

About the Author

David Steil | pharmaceutical market manager