Wednesday, December 1, 2010
Why The Swab Matters In Cleaning Validation
The U.S. Food and Drug Administration (FDA) issued its Guide to Inspections—Validation of Cleaning Process1 in 1993. Since that time, the protocols surrounding cleaning processes in pharmaceutical manufacturing environments and sampling and filling suites have received increased attention.2,3 The primary regulatory concern driving the need for cleaning validation is crosscontamination of the desired drug substance either by other active pharmaceutical ingredients (API) from previous batch runs or by residues from the cleaning agents used.
Cross-contamination with extraneous residues of any kind presents a safety risk to patients consuming the drug product. It threatens to alter the strength, chemical identity, and integrity of the drug substance and formulation. Therefore, the equipment and work environments involved in drug manufacturing processes must be cleaned at regular, prescribed intervals to prevent the possibility of such cross-contamination. These cleaning protocols must be validated in order to provide assurance that they do, in fact, serve their purpose—to clean the surfaces to a level that avoids the possibility of cross-contamination.
In recent years, increased emphasis has been placed on the development of validated and robust cleaning protocols given the concerns over the safety of our drug supply. Growth in the levels of outsourcing and off-shoring of pharmaceutical manufacturing has heightened the FDA’s concern over cleaning processes. Inadequate documentation, training, and validation of cleaning processes rank high among the four most often cited problems in Form 483 and warning letters that have been issued by the U.S. FDA.4
WHY SWABBING?
In a typical pharmaceutical manufacturing environment, cleaning might be performed by using 70% isopropyl alcohol (IPA) and/or other chemicals, detergents, and sanitizing agents in order to remove residues from the previous batch run. The areas thus cleaned must now be sampled adequately and appropriately in order to validate the cleaning protocol.
Swabbing and rinsing are the two most common techniques used for sampling of such cleaned surfaces. Swabbing is a direct surface sampling method, while rinsing is an indirect method. In practice, physical access to surfaces and parts of equipment to be cleaned tends to drive the choice of sampling method. For example, swabbing would work particularly well in more restricted work areas such as isolators, hoods, and accessible corners of equipment, while rinsing would work best in pipes and longer tubes. In general, a combination of both is most desirable in order to accomplish the most comprehensive coverage of surfaces to be cleaned.
While the FDA guidance indicates a preference for the more direct swabbing method, more recent communication from the International Conference on Harmonisation (ICH) ICH Q7A5 states that sampling methods need to be comprehensive enough to quantitate both soluble and insoluble residues that are left behind on the surfaces after cleaning. The exact protocols prescribed will necessarily vary depending on the nature of the products, residues, and surfaces. These protocols must be tailored to the needs of each environment.
THE SWABBING PROCEDURE – CONSIDERATIONS
The swab to be used for sampling is typically pre-wetted with water or another appropriate solvent in order to remove residues from the surface. Squeezing the sides of the swab against the inside of the vial upon pre-wetting prior to sampling removes excess solvent. This is important because excess solvent can itself serve as a source of residues leading to variable results. There is a direct, physical interaction between the swab, the solvent, and the residues to be removed; therefore, the choice of swab is critical to the effectiveness of the sampling process. The swab used must offer ultra-low particulates and fibers, high absorbency, and minimal extractable interferences. Polyester swabs are specially processed to meet the stringent requirements associated with cleaning validation protocols. The physical nature of the swabbing process implies that significant levels of operator training be conducted prior to implementation of cleaning validation protocols. This training should serve to minimize the subjectivity that is inherent to such sampling activity. The recommended directions and motions used in actual swabbing of an area as shown in Figure 1 should be detailed in the training to ensure the highest levels of consistency. Alternate swab sampling patterns may certainly be used if they would help maximize percent recovery.
A suitable extractable solvent is used to release the residues from the swab head. Depending on the particular SOP in each area, this swab sample may need to be filtered and/or sonicated to extract the residues as completely as possible. These sample prep procedures place a heavy premium on the intrinsic quality of the materials used in the swab head and the filters. The use of anything less than the highest quality of suitably pre-treated polyester swabs can prove to be a source of extraneous contamination in the subsequent assay.
The method development and validation steps are often conducted on test coupons to serve as examples of the equipment or surfaces to be cleaned. The choice of filter and solvent used in sample preparation is also critical since they can have an impact on the recovery, influence extractables, and efficiency of filtration. Yang et al. have reported a systematic study of a variety of solvent conditions and pH and their impact on the percent recovery and efficiency of filtration.6 While it may be intuitive to choose the solvent conditions used in the subsequent analysis (e.g. HPLC) as the extractable solvent, this may sometimes compromise the filtering efficiency and the percent recovery.
ANALYSIS OF RESIDUES–ANALYTICAL CONSIDERATIONS
The purpose of swab sampling as part of a cleaning validation protocol is to be able to prove that the cleaning process served its purpose. That purpose (cleaning the surfaces to avoid any cross-contamination) is best measured in the validation step as a percent recovery of seeded residue. Such a measurement provides an estimate of Residue Acceptable Limit (RAL). The measurement of percent recovery is accomplished through an analytical test, typically either HPLC (High Performance Liquid Chromatography) or TOC (Total Organic Carbon).
HPLC-UV systems commonly carry additional detectors such as mass spectrometry (MS - for specificity and identification). It is important to realize early in the method development process for cleaning validation that percent recovery will be directly influenced by the interaction of the particular assay detector with each of the variables involved in the protocol. It is best to conduct a pre-study of the influence of the various factors involved in the cleaning in order to ensure that their effect on the final percent recovery measurement is well understood. It is typically very cumbersome to deconvolute an aberrant percent recovery result ‘after-the-fact’ for a method that may have been in use over a long period of time. Cleaning Validation is a complex activity requiring a careful choice of sampling procedure and analytical method. It is therefore highly recommended to always use only the highest quality materials for swabs, filters, and solvents in cleaning validation protocols in order to assure that they cannot serve as sources of aberrant results, if and when those results do occur.
Both HPLC and TOC are highly sensitive methods that serve as assays for cleaning validation protocols. HPLC by its very nature is a specific assay in that it can identify peaks and assign them to specific residues, while TOC is a classically non-specific measure of overall carbon burden in a given environment. Since these assays are both quantitative, typical analytical parameters such as accuracy, precision, linearity, detection, and quantitation limits must be evaluated as part of method development.
While HPLC is a very commonly used tool in the pharmaceutical industry, the complexity, trace level sensitivity, and criticality of the cleaning validation protocol to drug safety merits special attention to the results from HPLC analysis. It is important to avoid using materials that might serve as sources of contamination through interference with the UV spectrum, or the detector of choice. In the event that such interference in the assay is unavoidable, understanding and perhaps even quantitating the interference so that the cleaning validation protocol is appropriately “sciencebased” would pass muster under an investigation. Attempts should be made to identify any additional peaks that appear in the chromatograms of swabextracted samples besides those arising from the expected residues.
TOC (Total Organic Carbon) is a conductometric assay that correlates with carbon concentration, which provides an overall, non-specific estimate of residue burden left behind on the surface from a previous batch run. TOC measurements are highly sensitive and typically reported at the part per billion (ppb, or μg/L) level. As such, great care must be taken during the swab sampling and sample preparation to minimize external sources of organic carbon contamination.
SUMMARY
Cleaning validation is an essential step in the critical cleaning of pharmaceutical manufacturing environments. Swabbing is the preferred method of sampling such surfaces in the process of cleaning validation. The sampling and analysis methods have a direct and measurable impact on the percent recovery results from either HPLC or TOC assays. It is critical to ensure that the swab, filters, and associated materials used during the process are of the highest possible quality and do not contribute even trace levels of impurities that can interfere with the results.
References
- Guide to Inspections of Validation of Cleaning Processes, FDA Office of Regulatory Affairs, Rockville, MD, 1993.
- Carlson, J. “Is swabbing a regulatory requirement?” Journal of GXP Compliance, (14):1, 2010.
- Pluta, P. and Sharnez, R., “Avoiding Pitfalls of Cleaning Validation.” Journal of GXP Compliance, (14):3, 2010.
- McCormick, D. “Poor OOS Review Leads Causes of FDA Citations.” Pharma Technol. Oct 2005
- ICH Guidance for Industry, Q7A; Good Manufacturing Practice Guidance for Active Pharmaceutical Ingredients, Aug 2001.
- Yang, P, Burson, K., Feder, D. and Macdonald, F. “Method Development of Swab Sampling for Cleaning Validation.” Pharmaceutical Technology, Jan 2005.
Basics of Isolator Cleaning
ISOLATORS AND DECONTAMINATION
Decontamination is the reduction or removal of biological or chemical agents, including non-active particles to non-hazardous levels to products, processes, or the environment by means of physical or chemical procedures.
Specifically in pharmaceutical manufacturing environments, research laboratories, and hospital pharmacies, the effective decontamination of biological agents like bacteria, viruses, fungi, protozoa, prions, and spores is essential.
Isolators like fume hoods, biosafety cabinets, and gloveboxes are used to create environments with low levels of environmental pollutants such as biological agents, aerosol particles, and dust. These separative devices have a controlled level of contamination, specified by the number of particles with a defined size per cubic meter, providing controlled environments that are specifically tailored to the needs of its operator. This classification of cleanrooms and isolators, however, is not taking into account specific requirements regarding biological contamination. In order to maintain the low levels of environmental pollutants, isolators have to be decontaminated on a regular basis.
ISOLATOR CLEANLINESS
Isolator cleanliness levels are defined by different classifications, shown in Table 1 and Table 2. These classifications are evaluating the environmental pollution by particles, however, not taking into account specific requirements regarding biological contamination. In order to maintain the low levels of environmental pollutants, isolators have to be decontaminated on a regular basis.
Quality supervisors in facilities using isolators have to determine the acceptable level of biological agents in their respective environment and decide on the method to achieve these levels. Several factors influence the choice of method and materials.
POTENTIAL CONTAMINANTS
Isolators are used in a variety of industries working with different material and under different requirements. Potential contaminants in isolators can therefore range from biological contaminants (e.g. pharmaceutical industry, hospital pharmacies), radionuclides (e.g. pharmaceutical industry, research laboratories) to general particulate contaminants (e.g. semiconductor industry).
CHEMICAL AGENTS: INACTIVATION
Spills of hazardous chemical agents in isolators or potential reaction products immobilized on isolator surfaces have to be inactivated or diluted to non-hazardous levels. The chemicals and chemical processes used for inactivation depend on the contaminant.
BIOLOGICAL AGENTS: DISINFECTION AND STERILIZATION
To reduce the level of biological agents in an environment, disinfectants/sanitizers and sterilants can be used. Sanitizers and disinfectants are terms used in different industries for the same kind of product. Whereas the food and foodprocessing industry uses the term sanitizers, the pharmaceutical industry, laboratories, and hospitals are predominantly using the term disinfectant.
Disinfection describes a process that eliminates many or all pathogenic microorganisms on inanimate objects, except bacterial spores.1 On the other hand, sterilization describes a process that destroys or eliminates all forms of microbial life and is carried out by physical or chemical methods.1 Depending on the biological agent and the material or media holding it, sterilization can be achieved through the application of heat, chemicals, irradiation, high pressure, or filtration. It is essential to understand the difference between both processes to assure that contamination level requirements of work environments are met. Whereas some commercial and technical literature is confusing readers by using both terms interchangeably, it should be noted that disinfection and sterilization describe two processes with very different requirements in outcome. It is not appropriate to talk about partial sterilization or even replace the word disinfection with sterilization.
The efficacy of sterilization depends on a number of factors like:
- prior physical cleaning (effective surface and biofilm reduction)
- presence of organic and inorganic load-level and type of microbial contaminants
- concentration of sterilant
- exposure time of sterilant
- pH, temperature, and humidity of environment
- geometry of objects and spaces
- physical properties of objects
The efficacy of different sterilization methods has been evaluated and reported by a number of publications. Tested microbial agents include bacteria, spores, and viruses.3,4,5 As discussed in these articles, microbiological agents may show a significant difference in resistance to the discussed sterilization methods. Therefore previously mentioned factors (the efficacy of sterilization depends on a number of factors such as in list one as well as the specific resistance of microbiological agents) play a vital role in the selection of the appropriate sterilization method.
(Click Image For A Larger Version)
CLEANING OF ISOLATORS
Decontamination or cleaning, the reduction or removal of biological or chemical agents, including non-active particles is a multi-step process that depends on the contaminant and the required cleanliness level.
In isolators with processes using chemical agents the successful inactivation of these agents precedes any removal attempt in order to avoid further contamination of the environment or reaction with the isolator surfaces and cleaning materials. After successfully inactivating hazardous chemicals, high absorbency wipes are used to physically remove the reaction products.
When choosing isolator cleaning tools and materials, it is recommended that operators introduce the least amount of particle and fiber generating materials into the isolator. Typically a cleanroom laundered 100% continuous filament polyester knit material with sealed edges is recommended for use to clean surfaces inside the isolator. Additionally isolator cleaning tools with replacement covers that have been tested for particle and fiber release are appropriate to extend the reach of the cleaning area as well as providing ergonomic benefits to the operator.
One can also use cleanroom wipes with specific surface treatments to allow the wiper to capture and retain particulate contamination, resulting in more efficient cleaning and reduced likelihood of recontamination of critical surfaces.
The recommended steps to be performed when cleaning a contaminated surface do not change and are the same for all kinds of contaminants.
- Always clean from the cleanest to the dirtiest surface.
- Clean with overlapping strokes and change wiper surface with each stroke.
- If using an isolator cleaning tool or mop, change out cover material with each surface side of the isolator.
CLEANING PROCESS SOP
Developing a Standard Operating Procedure (SOP) for your isolators is a difficult task and depends on the very specific requirements of a facility’s processes and regulation in its industry. As a rule of thumb, Table 3 can serve as a general guideline to develop your own SOP.6 Questions you should ask yourself are:
- What contaminants am I concerned about?
- Would they contaminate my processes (inside) or the environment (outside)?
- Are these contaminants inert, chemically-, biologically-, or radio-active?
- What contamination limits have to be considered?
SUMMARY
Proper decontamination and cleaning of isolators is critical to the long term success of materials produced in these environments. Reducing the risk of cross contamination starts with a full understanding of the type of potential contaminants introduced before, during, and after the production process. Sterilization and spraying with disinfectants alone are not enough to remove residual particles that could result in the buildup of biofilms. Proper wiping and rinsing protocols are needed to ensure the total removal of contaminants and the cleanliness of the isolator.
References
- Healthcare Infection Control Practices Advisory Committee (HICPAC), “Guideline for Disinfection and Sterilization in Healthcare Facilities,” 2008
- McDonnell, G.; Russell, A.D.; “Antiseptics and Disinfectants: Activity, Action, and Resistance” Clinical Microbiological Reviews, Jan. 1999, p. 147-179
- Mehmi, M.; Marshall, L.J.; Lambert, P.A.; Smith J.C.; “Evaluation of Disinfecting Procedures for Aseptic Transfer in Hospital Pharmacy Departments” PDA Journal of Pharmaceutical Science and Technology, Vol. 63, No. 2, p. 123-138
- Block, S.S. Disinfection, Sterilization, and Preservation. Philadelphia: Lea & Febiger 1991
- Siegerman, H. “Wiping Surfaces Clean” A2C2 Magazine, April 2003
- “Isolator Cleaning Guide” 01 Aug 2010 Berkshire Corporation
The Basics of Non-Evaporative Parts Drying
MAY THE FORCE BE WITH YOU
The second general method for drying parts of liquid films is to apply force to the films so as to dislodge them from surfaces. At least three types of force may be used: centrifugal, mechanical, and surface tension.
CENTRIFUGAL DRYERS
This approach makes too much sense to have been ignored in industrial cleaning. One simply places the parts in a circular-shaped basket, rotates the basket, the water is pulled off by the centrifugal force, and the dry parts are removed.
Relative to evaporation, energy consumption is negligible. Some heat air and blow it onto the rotating parts which makes no sense as the point is to avoid the energy debit necessary for evaporation. Cycle time can be 30 seconds to ten minutes.
There is mistaken concern about the force causing part movement within the basket, and therefore possible damage. Actually the centrifugal force holds parts in place and keeps them from moving.
Yet, there are good reasons why centrifugal dryers aren’t commonly used in critical cleaning: (1) not all water is removed, perhaps only 95% (which could serve as a preliminary drying step), and (2) most cleaning machines are built to use square baskets, and not circular-shaped ones.
MECHANICAL IMPACT WITH AIR
Long used in industrial cleaning, blowoff with forced cold air is low-cost and can be useful as a preliminary drying step. The operative device is called an air knife. It can be fed with compressed air at ~75 psi or with low pressure air at a velocity of hundreds of feet per second. The airflow is often referred to as an air curtain; in a cleanroom without an enclosure, it would be referred to as a particle spreading disaster! See Figure 1.
Most common applications involve high-production such as strip or sheet or other items on a moving conveyor.
MARANGONI DRYING
Useful only for perfectly flat surfaces, of which semiconductor wafers are the best example, this approach removes films of water without leaving residues.1
It’s based on an observation that there is a net surface force between locations (a gradient) where the surface tension is different. This force pulls thin fluid films from the location of low surface tension to the location of high surface tension.
Such a gradient can be produced by a difference in temperature between two positions. It can also be produced by a difference in composition. This is shown in Figure 2.
In a Marangoni dryer, silicon wafers are mounted in an open cassette box immersed in DI water. A tiny amount of isopropanol is added to the water surface at the top of the dryer.2 In other words, the surface tension in the top layer of fluid is made less than that of the fluid into which the wafers are immersed.
As the open cassette of wafers is slowly (~1 mm/min) pulled upward through the top layer of low surface tension, the water film on the surface of the wafer is pulled downward, and off the wafer. The dry wafer has no water on either side. No water-soluble materials (“spots”) have been left behind.
THE LAST WORD
There is one good reason why non-evaporative drying is practiced in critical cleaning. It is to remove water without leaving residues insoluble in water. Energy conservation has yet to be a factor in the costs of critical cleaning so that the two other schemes for non-evaporative drying are not considered. Perhaps in the future they will be.
References
- “Drying Without Evaporation – The Marangoni System”, Controlled Environments Magazine, June 2005.
- An excellent multi-page view of Marangoni drying process can be seen at,
www.feu.edu.tw/edu/mse/%E6%AA%94%E6%A1%88%E4%B8%8B%E8%BC%89/maragoni%20dryer.pdf.
Finding The Optimal Analytical Test Part 2
In the fall of 2009, as John Burke, Director of Engineering Services at Houghton International Inc., Valley Forge, PA, explains, ASTM was engaged as a neutral, consensus- driven agency to modify an existing ASTM TGA test, E1868-09.2 The ASTM activity was both rigorous and turbo-charged, because SCAQMD had to come up with a method in support of improving air quality that could be rationally communicated to the Federal regulators. Modified ASTM E1868-103 is now in place.
Burke points out that, compared with GC/FID, TGA is a relatively simple method. A fixed amount of material is added to a wing pan; the temperature is ramped up; and losses are determined gravimetrically. However, the devil is in the details and E1868-10 is no exception. Details include whether or not to begin data collection during the warm-up period, the three-dimensional configuration and material of construction of the wing pan, and the amount of liquid to be tested. Materials handling prior to test must also be specified; for example, Burke notes that fluids with a high solvent content can show evaporative losses prior to testing. “We used ASTM 691,4 including replicate samples and multiple labs to determine that we had a robust method. The tests were successful; they will be published.”
GC METHOD DEVELOPMENT
Naveen Berry, Planning and Rules Manager at SCAQMD, Diamond Bar, CA, notes that “if we had a standardized, reproducible method, we would have adopted Rule 1144 for all categories of metalworking fluids and lubricants in March 2009. “We held back on regulating metalworking fluids, especially oils and low viscosity oils with semivolatiles because the GC/FID test method was not ready for prime time. Together, industry and SCAQMD developed a TGA method that provides repeatable and reproducible results. SCAQMD is in the process of doing a second phase round robin with 313L. This will include academic, government, and private laboratories. According to our Board, for Rule 1144, we have yet to meet the robustness specified in ASTM E619. There are many variables that must be defined; GC analysis is a very fine art, as well as a science.”
MEETING TECHNICAL CHALLENGES
Burke adds that the next step is to reformulate metalworking fluids based on the new limits. He notes that vegetable-based lubricants tend to be naturally lower in VOCs than are naphthenic lubricants and therefore could be good candidates; he notes that relative reactivity may eventually provide a more meaningful estimate of the impact of volatiles on air quality. A conference at SCAQMD is planned to discuss lubricant options and real-world findings for ultra low-VOC technology, as well as test methods.
TAKE-HOME LESSONS
Testing is an evolving and collaborative effort. Within your own organization, consider assembling what regulators term the “stakeholders” and obtain their input. There is no one optimal analytical test, so we suggest evaluating the options on a scientific and practical level.
Rule 1144 has improved air quality. Berry estimates that “we eliminated a little more than 3.5 tons per day from this category alone, which is almost the equivalent of shutting down three of the Southland’s major oil refineries. These were very cost-effective reductions. It is fortunate that the rule has been developed rationally, because there are encompassing implications. California is a trendsetter,” concludes Burke. “We believe the rule will morph away from California and will be adopted throughout the United States.”
References
- SCAQMD Rule 1144, “Metalworking Fluids and Direct Contact Lubricants,” Amended July 9, 2010 http://aqmd.gov/rules/reg/reg11_tofc.html
- ASTM E1868-09, Standard Test Method for Loss-On-Drying by Thermogravimetry, http://www.astm.org/DATABASE.CART/HISTORICAL/E1868-09.htm
- ASTM E1868-10 was developed as ASTM WK26130 - Revision of E1868 - 09. http://www.astm.org/Standards/E1868.htm
- ASTM E691 Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
Why Clean the Cleanroom?
There may be fear of regulatory agencies or of customers. Cleaning most often relates to particles; increasingly, it is also concerned with Airborne Molecular Contamination (AMC) or with minimizing biofilms.
DESIGN
Effective cleaning begins with thoughtful design. For the product, this means avoiding or at least being aware of areas where contamination is likely to occur. For the cleanroom, it means consideration of materials and configuration that minimize contamination. As part of the design, we also include determining what processes will be conducted within the cleanroom and how process flow will occur. Cleanroom real estate is valuable; conducting as much cleaning as possible outside of the cleanroom is not only economical, but can also minimize cleanroom contamination.
PROVENANCE
Extrapolation is necessary, but it may not be sufficient. We may say that a new product is substantially like an existing one and use cleanliness standards and cleaning practices for the existing product as benchmarks for the new one. However, after a few generations of extrapolation, modified cleaning processes and other, more pertinent, tests for cleanliness may be required.
In cleanrooms, a design to be used for one application may not be readily adaptable to another. Cleanrooms are often reutilized for applications other than those for which they were originally designed. In such instances, it is important to take a dispassionate look at the previous use or perhaps misuse of the cleanroom and to take corrective action. It is also important to assess how the cleanroom is to be used and to make needed changes.
REQUIREMENTS
This means not just specifications and standards, but also actual performance requirements. Meeting a specification is not a substitute for logical analysis. Such analysis must involve the expected end-use of the product as well as an assessment of likely contaminants and of the consequences of contamination.
EDUCATION
Teaching employees to adhere to rules of behavior or to a specific cleaning protocol is necessary. However, for both product and cleanrooms, there is no substitute for understanding the “why” of the cleaning process. Education is important whether your product and cleanrooms are cleaned inhouse or are outsourced. In fact, when you outsource, educating the employees of the contractor may be even more important.
VIGILANCE
Monitoring and auditing are part of vigilance. However, monitoring and auditing are not sufficient, particularly with complex products. One reason for the importance of an educated workforce is that you have to expect the unexpected; and this is true for both the cleanroom and the product itself.
CLEAN CRITICALLY—IN AND OUT OF THE CLEANROOM
Too often, cleaning the cleanroom to a particular standard becomes an end in itself; reaching the goal or staying within limits of contamination may not be adequate. The ultimate goals—assuring cleanliness and quality performance of the product—are lost. We have to meet or exceed the requirements. In cleaning the cleanroom and the product, our goal should be to clean critically, to adopt valueadded cleaning. By the way, our view of critical cleaning is that it is a lynch-pin process, one that is essential to product quality. Therefore, critical cleaning may occur not only in the cleanroom but also very early in the fabrication and assembly process. But, more about critical cleaning next year.
Benefits of Nanofiber Particulate Air Filters
Nanotechnology is an emerging technology being investigated in many industries and Nanofibers are an important part.
As nanotechnology emerges into the industry, many future products are expected to improve performance as a result of new scientific developments. Nanofibers will play an important role in this new emerging technology.
Nanofibers are a thousand times smaller than human hair and are made from polymers in the form of spider web like structures, with a very large surface area and a large number of pores with very small pore size. The nanofiber, when combined with conventional filter media, creates a new class of media defined as “nanomedia.” Nonwoven nanomedia are revolutionizing the field of liquid and air filtration, and a number of companies are beginning to offer new solutions to customers using state-of-the-art nanotechnology.
In the case of HVAC air filtration, the fine mesh of nanomedia increases filtration performance significantly, thereby blocking smaller airborne particulates with marginal increase in resistance to air flow. The nanomedia are very fine and do not increase the weight or change the mechanical characteristics of the conventional media. Nonwoven nanofiber media are typically made using an electrospin process, whereby nanofibers are laminated to the microfiber media similar to filter media widely used in today’s particulate air filters. These nanomedia are being used in dust cartridges, bag filtration, vacuum bags, chemical-biological warfare filters, and air conditioning filters as well as many other filtration applications.
SOME COMMONLY ASKED QUESTIONS:
How do the nanofibers improve HVAC filtration?
The thin layer of nanofiber web forms a barrier for particles while allowing the air to “slip” through the large volume of small pores. The large surface area of the nanofibers traps smaller particles, while air slips through the particles and filter medium.
Since nanofiber traps more submicron particles, will they “load up” the filter quickly and need frequent replacement?
The first nanofiber filter may load up very differently from conventional filters, however it really depends on the particle size and count in the air. For example, when three stage Minimum Efficiency Reporting Value1 (MERV) 11, MERV 13, MERV 14 nanofiber-based air filters were tested in a welding institute, and compared with a conventional filter, the nanofiber filters were becoming caked as most particles collected were condensed metal fume particles. Particle measurements of the air prior to filter installation were in several millions (0.3-0.5 microns particles). Most particles were generated as a result of welding fumes and the grinding of metal parts. A significant decrease in particle count was measured while air quality was improved. It is also important to note that, because of a higher surface area in these filters, we were able to replace very large air filters with smaller ones—for example a 24x24x12 filter was replaced with a 24x24x4. Hence, as a result of nanofiber technology we were able to improve the air quality and reduce the size of the filter, thereby making it easier for customers to handle the filter during the installation and disposal process.
During tests in a large hair salon, for example, we found that filter changes were needed on a monthly basis since a large number of haircuts, color treatments, and perms are performed at that location. The nanofiber filters may be the least expensive air filter available to trap short pieces of human hair. The nanofiber filters have been the only filters that actually stop human hair from getting into their ductwork. The added benefit of reducing fumes from the color and perm mixtures is a plus. Those fumes are typically in the E2 range where MERV 13 filters are at least 90% efficient.
In our field test(s) ranging from hospitals, manufacturing environments, cleanrooms, to allergy applications, our findings show that where smaller particles need to removed from air, nanofiber-based air filters have been superior in cleaning air.
Will the nanofibers come off and circulate in the air without being seen?
Since nanofibers are very small, only a few milligrams of spaghetti form are added onto a micron-sized substrate (i.e., conventional filter media) to achieve the desired performance. These continuous nanofibers are glued to, or encapsulated in, the microfiber media. When the media is assembled to form filters, the nanofibers are either “upstream” or “downstream” of the air flow depending upon the applications calling for “depth” or “surface” filtration.
Extensive testing on a 24x24x2 air filter in a wind tunnel at 2000 cfm air flow at 492 feet per minute face velocity per ASHRAE 52.2 test standards shows that when nanofibers are encapsulated or glued and are “upstream” of air flow, there is no evidence of nanofiber delamination and/or becoming airborne.
SOME INFORMATION ABOUT NANOFIBERS
Nanofiber air filters improve E1 (0.3 to 1.0 microns) efficiency
Filters that begin to block submicron-sized particles (0.3 to 1.0 microns) are usually rated by the ASHRAE 52.2 test standard as MERV 13 or higher. Typical particles of submicron or nano size are: radon progeny, coal flue gas, oil smoke, resin smoke, tobacco smoke, sea salt, metallurgical dusts and fumes, carbon dust from graphite, viruses, bacteriophages, and cornstarch.2 An ASHRAE 52.2 test standard report will give a filter efficiency in three particle sizes. These Particle Size Efficiencies (PSE) are called E1, E2, and E3. The sub - micron-sized particles are in E1. Research demonstrates that nanofiber-based air filters trap more fine particles (E1) compared with conventional air filters.
Nanofibers Breathe
The ASHRAE 52.2 test standard allowed final pressure drop is 350 Pa (1.4 inches water column) for air filters rated at MERV 13 to MERV 16.3 Initial new filter pressures are usually about half the final pressure. Nanofiber particulate air filters rated at MERV 13 have an initial pressure drop of 0.34" W.G. Nanofibers are being used in special fabrics because they breathe while protecting skin with a microscopic filtering mesh.
Nanofiber Filters May Save System Energy
The higher the pressure drop, the harder your system fan will have to work to deliver conditioned air. The harder the fan works, the more you pay for energy. A rule of thumb is a 1 Pascal increase in pressure has an annual cost of 1 Euro in additional energy.4 A filter with only 50 Pascals (0.2 inches of water) pressure drop could cost over $60 more per year in system energy use.
THE FUTURE OF NANOFIBERS
Developing Carbon Nanofibers
Experiments are underway to develop manufacturing scale processes to turn electro spun nanofibers into Carbon nanofiber (CnF) and Activated Carbon nanofiber (ACnF). Activated carbon nanofibers can be tailored to capture volatile organic compounds (VOCs) and Toxic Industrial Compounds (TICs). Custom filters in the near future may not only be a special size, but they may also be manufactured to attract specific compounds using these nanofibers integrated with nanoparticle based adsorbents. These latest experiments to develop carbon and activated carbon nanofiber commercial scale manufacturing processes is being funded in part by a 2009 Technology Innovation Program (TIP) award from the National Institute of Standards & Technology (NIST).
What value does nano truly add and what is the value proposition to HVAC technology?
If nanofiltration is important, ask your filter suppliers “What is your E1?” That is short filter lingo for what is the efficiency of your filter in the 0.3 to 1.0 micron particle size? MERV ratings are exactly what they stand for—the Minimum Efficiency Reporting Value. The next question to ask is “What is your pressure drop?” The higher the pressure drop, the harder your system fan will have to work to deliver conditioned air. The harder the fan works, the more you pay for electricity.
CONCLUSION
As more and more companies develop and use nanotechnology in filtration, we expect filters with nanofibers, nanoparticles, and other nanomaterial to penetrate the market. We expect new nanotechnology integrated products to improve its performance in terms of particulate, odor, and toxic chemical filtration. Additionally, products are expected to become smaller, thinner, lighter, and have superior life cycle costs.
Photographs provided by eSpin Technologies, Inc. ©
References
- ANSI/ASHRAE 52.2-1999 (1999) “Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size,” published by Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.
- NAFA Guide to Air Filtration, Fourth Edition, 2007
- Zhou, Bin and Shen, Jinming. “Comparison of General Ventilation Air Filter Test Standards between America and Europe.” International Network for Information on Ventilation and Energy Performance. Date accessed 08Sept2010. http://www.inive.org/members_area/medias/pdf/Inive%5CIAQVEC2007%5CZhou_5.pdf.
- http://www.camfilfarr.com/cou_us/energysavings/The-cost-ofclean-air.cfm accessed on 08Sept2010.
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