Defining Air Quality Requirements: A Cost/Value Approach
Using cost and value as guidelines, this article examines how to determine air quality requirements for your manufacturing environment–whether in the electronics, food processing or pharmaceutical industries.
By Hank Rahe
The following discussion will seem elementary to many readers, but is nonetheless important because it forms the basis for determining a working classification of the production environment. With the exception of aseptic pharmaceutical products that fall under the June, 1987, “Guideline on Sterile Drug Products Produced by Aseptic Processing,” the decision on air quality is economic.
In the case of aseptic pharmaceutical products, the FDA`s Center for Drugs and Biologics and the Office of Regulatory Affairs provide guidance as to the importance of the environment quality in terms of particulate content of the air. This will be covered in more detail later on in discussions of different industries and their use of defined air quality environments. For other industries, the air quality determination is a function of expected yields versus the cost of creating the desired environment.
It should be noted that techniques such as unidirectional air flow and barrier isolation are also used for operator protection. In these cases, however, environmental conditions are not defined in terms of air quality classifications.
Federal Standard 209E defines the requirements for classes of air quality as relating to the number of particulates of a given size present in the environment. The standard includes a table that defines class limits in particles per cubic foot, based on particle-size ranging from 0.1 to 5.0 micrometers. The number of particles present is a function of the integrity of the enclosure, the air filtration system, and the number of particles being generated within the environment. Each of these ingredients plays a role in the classification of the area.
The enclosure acts as a barrier to prevent materials outside the system from entering the environment. Key elements of the facility`s section are the ability of the wall and ceiling system to not generate particles, and to prevent outside particles from getting into the facility. In a perfect world, the enclosure would be completely closed; in the real world, however, there is a need for utilities and materials, as well as interaction with the activity or process being performed within the facility. The ability to control these elements in terms of potential particle generation is key to creating and maintaining the desired environment.
Preventing particles from entering the environment can be accomplished by sealing potential egress points where utilities are fed through, cleaning materials before entering the environment (reducing the number of particles introduced), and minimizing interface with people, typically the primary particle generators. These reductions will reduce the challenge to the filtration system.
Enclosures can take many forms–from open areas with no wall systems for support to totally closed systems that have controlled entrance and exit schemes for materials and people`s interaction through glove ports or half-suits.
Filtration and air handling systems can serve several functions, ranging from providing a barrier via high velocity air movement, to its primary function of cleaning the air within the environment by moving it through a proper filtration system. This air movement is unidirectional and should sweep the particle generation source towards the filters.
The quality of filters is defined by their efficiency ratings. These ratings describe the percentage of particles of a defined size that the filter media will capture. The term “HEPA” (High Efficiency Particular Air) describes a filter media capable of capturing at least 99.97 percent of particles greater than 0.3 micron in diameter.
The filtration system`s ability to achieve and maintain a given classification of air quality is a function of the system`s ability to remove particulates at a rate that approximates the generation rate less the desired classification. The velocity of the air and the percentage of surface covered by filters are the factors designers use to achieve the desired classifications.
The final and most important consideration is the amount of particle generation within the environment. Sources of this particle generation are usually people and equipment placed in the environment to accomplish a given task. In most cases, particle generation from equipment can be defined in terms of amount and location. Suppression or control of these sources can be achieved by a number of means, including local capture and unidirectional control of particulates away from the critical operation. People offer more of a challenge to the environment because of the potential for improper or inadequate gowning, procedural violations, and random movement. In fact, in most environments, they are the largest potential source of contamination.
Industry Air Quality Requirements
A number of different industries have defined air quality needs for the production of their products on a cost/value and regulation basis. This section will examine air classifications and the means used to achieve the needed environment in the electronic, food, and pharmaceutical industries.
The electronics industry has tied component yields directly to the level of airborne contamination present in the manufacturing area. This direct cost/value relationship has created facilities that are orders-of-magnitude cleaner in terms of air particulate quality than those in the food and pharmaceutical industries.
Based on product yield per given air quality, electronic component manufacturers are testing the bounds of technology to achieve cleaner environments. A recent CleanRooms article, “Digital`s New Fab 6 Weighs in at Sub-Class 1,” (p. 1, July 1995) describes a facility 35 times cleaner than Class 1 in real-time operating mode.
Control of particulates in both the food and pharmaceutical industries is based on providing aseptic products for control of viable and nonviable particulate that could injure the individual using the product.
The baseline for both industries is set by regulation, the standard being a Class 100 condition in the critical zone where product could be exposed. The ability to exceed the level of quality assurance provided by Class 100 conditions has recently been a topic of much discussion, turning pharmaceutical companies to barrier isolation technology. The economic impact of barrier systems is causing companies to move beyond the Class 100 standard, and further development of barrier technology may at some point approach the quality assurance level provided by terminal sterilization!
Cleaner processing for the food industry has evolved because of the reduced use of preservatives as a direct result of regulation and consumer demand. The use of higher quality environments has reduced the bacterial challenges inherent in producing preservative-free goods. In many cases, these processes also have a “yield-to-cleanness” curve.
Facility Cost Considerations
Providing a proper working environment for a production facility includes such key elements as the enclosure, the air filtration system, and internal particle generators. The cost of each of these items will help establish the cost portion of the equation, which can then be compared to the value of individual products to determine which classification offers the greatest benefits.
The Cost of Shell Construction. According to Scott Mackler of Clestra Cleanroom Technology (N. Syracuse, NY), the cost of modular-style construction is comparable to stick-build, when all factors are considered. However, the modular approach offers faster and cleaner initial construction, plus more long-term flexibility. Considering differences in cost based on desired air classifications, the cost of shell construction to provide increased air quality impacts total cost by less than 10 percent. This is a baseline number, given the same conditions, facility, and regulatory requirements.
Considering cleanroom alternatives provided by barrier/isolation systems, the cost of the shell for the system is proportionate with that of conventional cleanrooms.
Air Filtration Systems Cost. The cost of air filtration systems includes not only the filter system itself, but also the delivery and conditioning systems. The great variety of requirements placed on this portion of the equation results in a large cost variability. The system requires complete definition in order to make an accurate comparison between alternatives. When looking at cost impact, the following areas must be considered: percentage of filter coverage required to achieve the desired air classification (see Fig. 1); quality of filtration materials in terms of percentage efficiency and particulate-size capture ability, conditioning requirements, ability to recirculate, and most importantly, particulate-generating sources.
Internal control and capture of particles requires an understanding of source generation and the impact of air flows within the environment. A good understanding of these factors allows efficient implementation of control measures. The use of local exhaust and air sweeps in preventing particles from escaping into the general environment reduces the number of particles to be controlled. These strategies can be used on equipment placed in the environment. Basic to the system is the elimination of particle generators by removing generation sources wherever possible.
Making Cost Effective Decisions
Cost effective decisions start with understanding the baseline requirement in terms of air quality required in the manufacture of product. This minimum may be either a regulatory requirement or a level at which acceptable parts can be produced. It becomes the starting point for defining incremental improvement achievable by increasing yields or reducing rework. The data generated forms the vertical axis (see Fig. 2) for determining a cost-effective operating environment. The horizontal axis is the cost of achieving the air quality classification. This cost is complicated by the number of different ways for achieving air quality classification. The above discussion points out a means of ordering an approach to achieve the necessary environment at a minimum cost.
Shell decisions do not result in considerable cost differences, thus project resources need not focus a great deal of energy in this area (other than assuring the level of integrity needed to meet the given air quality).
In order to control particle generators, both machines and people need to be evaluated in conjunction with the filtration system design, since they have a direct effect on air filtration systems. Machine particulate control can be evaluated either by modeling or actual testing. Two levels of control that have different costs should be selected to test the impact on the filtration system cost. Because this is an interactive process, the important consideration is the least expensive method versus the more expensive difference in cost. Small differences are probably worth the cost of fine-tuning the initial solution.
Decisions on controlling the more variable “people” factor should also consider the cost of failure in terms of safety and effect on continuing operations. Maximum effort should be taken to eliminate this variable if a breach in product integrity represents a risk to the health and safety of workers or consumers.
Having determined the level of potential particulate generation within the facility, a filtration system can now be selected, and with the above factors defined, a cost/value graph constructed. This procedure not only results in good decision-making, but also acts as an excellent communication tool for explaining project cost to management. As an approach, it requires more up-front work and information gathering than more traditional approaches, but it will consistently deliver the most cost-effective level of air quality for your application.
What is the best air quality environment? It depends! n
Hank Rahe is the director of technology at Contain-Tech (Indianapolis, IN). He has nearly 30 years of technological experience, including project management and publicizing and presenting seminars. He is on the board of directors of the International Society of Pharmaceutical Engineers (ISPE), a member of the CleanRooms Technical Committee, a senior member of the Institute of Environmental Sciences (IES), and a member of the CleanRooms Editorial Advisory Board.
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Figure 1. Air filtration system costs are determined, in part, by the percentage of filter coverage required to achieve the desired air classification.
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Figure 2. To make cost-effective decisions about air filtration systems you need to understand the baseline requirements of the air quality for your manufacturing process. (This is an example only. Actual figures will vary by project.)