Case Study: Using Surrogate Testing to Determine Selection and Performance of Contained Dust Collection Systems

by David Steil

Introduction

The proper selection and operation of contained dust collection equipment is critical to pharmaceutical plants for a host of reasons, from environmental requirements and employee health and safety to production cleanliness and efficiency. The use of surrogate testing is a valuable tool in ensuring that contained dust collectors are meeting the requirments for containment relating to the hazards associated with the materials being processed and any applicable good manufacturing practice.

What is surrogate testing and why is it necessary? Historically, no performance data 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 entities determine if the equipment will meet required guidelines and standards for a specific project. Surrogate testing involves the use of a substitute or surrogate compound to simulate an Active Pharmaceutical Ingredient (API) for verifying the effectiveness of dust containment options for handling hazardous materials. Test conditions are designed to mimic workplace operations as closely as possible without incurring the expense or health concerns of handling the actual API. This case study describes how a pharmaceutical manufacturer, who shall be referred to as the "customer," dust collection equipment supplier, and a certified independent laboratory together employed surrogate testing to validate performance of a planned dust collection system that would serve a new manufacturing area.

The Role of Surrogate Testing

In selecting dust collection equipment for pharmaceutical applications, it is critical to understand the toxicological properties of the material to be captured, i.e., the potent, toxic or allergenic properties of the compound as it relates to personnel exposure. This determines 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 Time Weighted Averge (TWA), to which a healthy worker can be safely exposed for an 8-hour shift, 40-hour work week, without potentially suffering adverse health effects. 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. There are several benefits to conducting a surrogate test program, but the most noteworthy is the ability to verify effectiveness of isolation and containment equipment. Surrogate testing makes it possible to verify at different points in the evaluation and purchasing process whether the contained dust collection equipment is performing as needed for the project. This is accomplished by manipulating the test compound to simulate workplace operations and performing air and surface sampling during the operational manipulations.

Testing can be performed on equipment handling an API with unknown toxicological properties, as in this case study example, or for verification of existing systems. Surrogate testing also can be performed during Factory Acceptance Testing (FAT), again as illustrated in this case study, and/or Site Acceptance Testing (SAT) after equipment has been purchased to ensure proper performance once installed. By validating equipment performance during the engineering phases of a project, pharmaceutical manufacturers stand to reduce costs while also reducing risk.

Equipment to Be Evaluated

The equipment selected for evaluation by the customer was a cartridge-type contained system designed for high efficiency collection of dry dusts. This equipment is suited to a variety of pharmaceutical dust collection applications including tablet presses, coating machines, fluid bed drying, spray drying, blending, granulation, central vacuum systems, and general room ventilation. The equipment to be tested contained four cartridge filters rated at 99.999 percent efficiency (MERV 16) on 0.5 micron particles and larger with the capability to handle risk-based category 3, 4, and 5 compounds with OELs less than 1.0 µg/m³ for an 8-hour time weighted average.

Figure 1. Dust collection equipment used in the surrogate test.

Any point of potential exposure to hazardous dust must be enclosed and maintained so 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 the 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 angled hopper below during automatic pulse-cleaning.

The surrogate testing commissioned by the customer was a Factory Acceptance Test (FAT) to verify performance. It was conducted with the idea that if the equipment did not function as expected, it would be easier to address modifications at the factory rather than at the customer site. The supplier's stated claim was that the equipment would perform at or below the standard threshold limit of 1.0 µg/m³ for a TWA.

There were three possible outcomes to the surrogate testing depending on the equipment's measured capability to meet this desired containment threshold:

1. If results met or exceeded expectations, the customer would accept the contained dust collection equipment as designed.
2. If results were close, but not quite within the required range, the supplier would make modifications to the equipment and then repeat the test to verify if those changes were successful.
3. In the unlikely event that the equipment fell short of performance goals even after modifications, the customer would perform a risk assessment to determine the need for supplemental Personal Protective Equipment (PPE) or for other, more costly containment technologies.

The dust collection equipment is shown - Figure 1.