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- Air Filtration -
9/27/04 re: HEPA filter system function I am a BioMedical Equipment Technician for the United States Navy, currently deployed to a field hospital in Camp Arifjan Kuwait. Our Operating Room has a HEPA filtration system on it. The Units blower is rated at 2000 CFM and filter is rated at 1150 CFM / .1-.3 micron. My question is will this affect the filtration quality? Will the blower being rated higher than the filter cause it to lose effectiveness or will it just limit the amount of air being blown into the room? To help respond to your question, I obtained input from Dr. Robert Wood of Johns Hopkins Univ., an expert in environmental control measures who has published studies about the use of HEPA filter systems in this regard. His response is enclosed below. My impression from his comments is that your system will not dysfunction with the combination of blower and filter you described. However, in your system the efficiency will be at the level of the filter employed.
Dr. Wood's response:
The filter will function at the capacity of the filter. This really does not compromise the overall function so there is not a problem with the different capacities.
10/31/02 re: Choice of air filtration devices I'm an internist in practice in Baltimore. I would like your opinion on home air purifiers--which of the many are allergist recommending and why. Are combination purifiers/ humidifiers of any value.
I have enclosed below a review I wrote for the Current Literature section of this AADMC website. The article reviewed was written recently by Dr. Robert Wood of Johns Hopkins, an expert in environmental control measures. To obtain more information, I suggest that you read the entire article containing Dr. Wood's thoughtful discussion of the subject. The journal article can likely be obtained through your hospital library. Air filtration devices in the control of indoor allergens
Summary
There continues to be great interest and aggressive advertising of air filtration device (AFD) aiming to help in the control of indoor allergens. This subject was reviewed by Wood of the Johns Hopkins Medical Institutions in Baltimore, MD. He pointed out that there is very limited definitive evidence to support the use of AFD in indoor allergen control. A variety of AFD have been marketed, mainly 1) electrostatic recipitators or 2) high efficiency particulate air (HEPA) types. Individual room units of adequate size tend to be more effective in that room than units placed centrally in the forced air system because the individual room units filter air more extensively in the room involved (assuming doors and window are kept closed).
Most of the controlled studies have dealt with room-sized units. HEPA/AFD can be very effective in reducing airborne levels of animal allergens, especially when carpeting is removed or cleaned thoroughly and frequently (see below). In contrast, any AFD has much less effect reducing airborne levels of dust mite or cockroach allergens. Dust mite and cockroach allergens are carried on larger particles that do not remain airborne for any length of time and are therefore less likely to be trapped by AFD. The concomitant frequent use of HEPA filter-equipped vacuum cleaners further reduces airborne animal allergen levels considerably.
The limited studies of the effects of AFD use in the home containing pets on asthma symptoms in individuals allergic to those animals have shown modest if any benefit of HEPA/AFD compared to placebo filtration. However, in one study there was a modest increase in PEFR and decrease in bronchial reactivity after 3 months use of the HEPA/ AFD. The author of this review concluded that the role of AFD on the control of indoor allergens is not defined. If benefit is seen, it is mainly related to reduction in the levels of animal allergens but this is not a true alternative to removal of the pet from the home if the patient is very allergic to those animals. Additional controlled studies, including assessment of effects of AFD on indoor mold levels, are needed.
Reference
Current Allergy Reports 2002; 2:397-400
Editor’s Comments
This thoughtful discussion by an expert in indoor environmental allergen control helps emphasize how little is known about the clinical effects of AFD in respiratory allergies. Yet, there has been extensive marketing and resultant use of these AFD by patients/families anxious to avoid the rigorous measures such as removal of all floor covering, impermeable covering of the mattress, appropriate washing of bedding and pet removal from the home. The recent findings that cat allergens can be transferred from such homes on the clothing of school children to the classroom environment raises the potential that very cat allergic classmates may be affected by contact with such "cat allergen carriers." Theoretically, one would expect that the use of a HEPA-equipped vacuum cleaner would be very helpful in reducing surface levels of allergens (dust mite and cockroach as well as animal) from floor covering and soft covered couches and chairs. Some of these vacuum cleaners have been shown to be reasonably effective, provided that there is a tight sealing of the airflow through the vacuum cleaner unit (not always the case). However, it is not yet clear whether use of such vacuum cleaners is an adequate substitute for removal of floor covering and over-stuffed furniture from the room.7/2/01 re: Value of cleaning ductwork in aeroallergen avoidance Of what benefit is cleaning of the air ducts in a residential heating and air conditioning ventilation system? I have had several patients ask if it is worth the couple of hundred dollars to have the ducts cleaned to help control their (or their child's) asthma/seasonal allergic rhinitis. The only information I found was in an article which referred to the 56th annual AAAAI meeting where the cleaning of air ducts in the home to reduce animal allergens is of limited value. What about molds?
Most investigators of allergen avoidance measures have concluded that measures such as HEPA filtration and air duct cleaning are of only modest if any benefit in reducing the levels of dust mite allergens in rooms such as bedrooms. This is because most of the dust mite allergen is settled on the surfaces of bedding, carpets, etc. to which the person is locally exposed. The mite allergens are suspended in the air only transiently and locally around the source and are not circulated in large amounts through the air handling system of the dwelling (see the enclosed review by me of a review by Tovey et al, leading investigators of allergen avoidance. Also see my responses to previous Ask the Expert questions in this area by clicking on the "allergen avoidance" and "air filtration" key words in this Ask the Expert section). The subject of airborne mold levels is somewhat different and more complex. As you may know, it is felt that most of the molds found indoors actually come in from the outside and proliferate in areas of high humidity. Some investigators feel that markedly increase airborne mold levels may contribute to the "sick building syndrome" (see enclosed abstract). I have not seen an appropriately controlled study directed specifically to the effects of air duct cleaning on mold levels. However, I suspect that any modest benefit achieved would be not as impressive as attempts to reduce indoor relative humidity to below 50% at all times. Since high-humidity home environments frequently are secondary to wet basements, an aggressive attempt to eliminate water entry into the basement from rainstorms should be made. Use of dehumidifiers that drain into a sink or other outlet is also helpful. When mold/mildew is still present in sizable amounts, cautious use of evaporating fungicide crystals (e.g., paraformaldehyde) in a air-sealed basement room may reduce the airborne mold levels for a period of months. Any room treated in such a way should be well ventilated afterwards for at least a day before it is used. As noted in the enclosed abstract, frequent replacement of filters and cleaning of exposed parts of the air handling system with bleach-containing materials may reduce mold/fungal levels transiently. All these measures involve considerably less expense than the duct cleaning services which are aggressively marketed in some areas. Methods and effectiveness of environmental control
Summary
There has been great interest in and emphasis on the sensitization to aeroallergens such as house dust mite (HDM) as a risk factor in asthma. It is generally (but not universally) agreed that effective HDM avoidance measures will improve asthma outcomes in HDM-sensitive individuals. But what measures are most effective? This subject was reviewed by Tovey et al of the University of Sydney in Australia. They stressed that avoidance measures related to bedding is most important with suitable encasements, washing sheets/blankets at >130 F (to both kill the HDM and wash away allergens. Removal of floor covering and frequent wet washing of smooth floors is also helpful. Chemical treatment of carpets is expensive and generally insufficiently effective in lowering HDM allergen levels to non-pathogenic levels. Vacuuming with tightly sealed units, good filters and double-thickness bags may yield modest additional benefit. Air filtration generally does not add much for HDM removal because of the short time that HDM allergenic particles are airborne after each air disturbance. Air filtration can be more effective in removing furry pet allergens but the clinical benefit of this is debatable.Reference
J Allergy Clin Immunol 1999;103:179-91Editor's Comments
We have reviewed a number of studies in this area (see Current Literature Section). I found this one of the best, well-balanced reviews of this subject in which there is sometimes more enthusiasm and advertising "hype" than solid documentation. As the authors point out, acaricide sprays and other devices reputed to reduce allergen levels within the home are being increasingly marketed Many measures are time consuming and expensive and of doubtful efficacy. This review is worth reading before advising patients!Appl Occup Environ Hyg 2000 Aug;15(8):635-43
Resolution of sick building syndrome in a high-security facility.
Hiipakka DW, Buffington JR.
U.S. Naval Hospital, Rota, Spain.The main objective of this article is to serve as a case study for other industrial hygiene (IH) professionals' review as a "real world" effort in responding to a facility perceived as "sick" by its occupants. As many industrial hygienists do not have extensive backgrounds in evaluating microbial air contaminants or the mechanical function of building HVAC units, the overall intent is to provide "lessons learned" to IH generalists who may be asked to participate in indoor environmental quality (IEQ) surveys. In September 1994, a suspected case of "sick building syndrome" was investigated (with significant airborne fungal loads confirmed) at a communications center after numerous occupants reported upper respiratory disease and/or allergy-type symptoms. The setting was a two-story structure approximately 30 years old, with a normal occupancy load of 350 to 400 persons. In addition to continual structural modifications, the central HVAC air conditioning systems had poor maintenance histories. Inspection of HVAC components revealed visible fungal growth on air filters and air ducts and in cooling fan condensate drip pans. Fungal air samples were collected with an Anderson N6 air sampler and Sabouraund dextrose agar media. Over a study period of 23 months, three rounds of 26 air samples were collected for 5 minutes each at 28.3 liters/minute airflow. Cultures exhibited fungi such as Aspergillus, Penicillium, Alternaria, and Cladosporium. Certain strains of these fungi produce mycotoxins that may cause a variety of deleterious health effects such as those described by occupants. Initial 1994 airborne fungal concentrations ranged from 85 to 6157 colony forming units (CFUs) per cubic meter of sampled air (CFU/m3). Some investigators have reported fungal concentrations as low as 245 CFU/m3 associated with complaint sites in other buildings. Remediation efforts involved hiring a dedicated mechanic to implement a HVAC preventive maintenance program (including regular replacement of all HVAC air filters and cleaning of accessible components with water/bleach solution). Post-abatement January 1996 re-sampling revealed a significant drop in airborne fungal colonies up to 97 percent (range = 21 to 1092 CFUs/m3)—which also coincided with physicians at the local hospital sensing a qualitative reduction in patient visits from facility workers. To address seasonal bias, a final August 1996 air sample round revealed a range of 14 to 500 CFUs/m3. Of the 21 workspaces sampled in all three rounds, nine continued to show a decline in CFUs/m3 from September 1994 baseline counts. These results demonstrate the critical role of an ongoing HVAC maintenance program for reducing potential reservoirs of fungal organisms in indoor work environments. Building renovations (especially those involving major changes to building layout and usage) can adversely affect IEQ if plans do not include coordinated updates and regular preventive maintenance of HVAC systems. Eventual negative outcomes can be reduced occupant productivity and deleterious health effects.
3/17/99 re: Heating system filtration I have a patient with dust mite allergies who want to change her heating system. She has a hepa filter on the forced hot air system and individual room hepa filters. Also the home has hardwood floors and minimal carpeting. Do you know of any recent studies comparing baseboard hot water heat or radiant heat to the forced hot air? Unfortunately, evidence from recent studies indicates that HEPA filters reduce the mite allergen content in rooms like bedrooms only modestly because mite allergens tend to accumulate on surfaces and are not suspended in sizable amounts in the air. For that reason, avoidance measures such as removal of carpets or rugs, use of impermeable covers on mattresses and box springs, and synthetic bedding, when feasible, are more helpful. Washing all bedding at temperature of at least 130vF (when feasible) will at least partially denature the mite allergen. However, I find that there are other effects of different heating systems. Dust mites tend to replicate less well on drier environments. For this reason, maintenance of a relative humidity less that 45-50% reduces mite allergen levels. However, I find that excessively dry heat air(<20% humidity) in the winter months is irritating to the airways. Both forced air and electric heating tend to really dry the air. Insertion of a central humidifier in a forced air system will help but one has to be sure that molds do not grow in the reservoir. Also the forced air may contain any irritants present in the duct work, etc. (which may be removed by HEPA filters). Therefore, my first choice would be a hot water radiator system.
2/16/99 re: Benefits of room air ionizers in allergic respiratory illnesses Many of my patients ask frequently regarding any potential benefit from room ionizers. From the limited medical literature available and articles from Consumer's Report, I have not been able to find any evidence for beneficial effects in treating allergic respiratory illnesses. Please comment on this question and I would appreciate any references or information to provide to my patients. Although there was enthusiasm in some quarters for the use of negative ionization in the entrapment of airborne allergens years ago, most studies have found this approach much less effective than the newer high-efficiency particulate (HEPA) filter devices. Unfortunately, even standing HEPA filters of adequate size (and frequently sizable noise level) are of only limited benefit because the major indoor aeroallergen, dust mite, is present mainly on surfaces and not continuously suspended in the air. Also, a recent study by Wood et al of Johns Hopkins showed no dramatic reduction by HEPA filtration of cat allergen-induced respiratory symptoms.Therefore, the major preventive approach to dust mite allergens is removal of floor covering, mite-proff enclosures for mattresses, pillows, etc, frequent washing of bedding in hot water, and avoidance of excess humidity and clutter/dust catchers in the room. The practical value of HEPA-equipped vacuum cleaners and use of acaricides/denaturants of the mite allergen is more debatable, according to the recent studies.
REFERENCES - J Occup Med 1991;33:681-687 and Am J Resp Crit Care Med 1998;158:115-2011/13/98 re: Information about HEPA filters Where can I find reliable information about indoor air filters? Patients frequently ask me about the relative benefits of ionizers and HEPA filters for improving indoor air quality. I suggest that you read the recent article (Am J Resp Crit Care Med 1998;158:115-120) by Wood et al in Johns Hopkins University, one of the leading investigators of the epidemiology of indoor aero allergens. I agree with their conclusion that use of HEPA filters by themselves do not reduce airborne levels of allergen containing particles to a degree where symptoms due to allergic reactions are eliminated. It is far preferable (though more tedious) to carry out strict avoidance measures, including removal of offending animals from the home. An American Lung Association Committee came to a similar conclusion. HEPA filters may have an adjunctive role in addition to allergen avoidance. Such filters, if adequately sized/powered may also reduce levels of some irritants, such as those in cigarette smoke. I know of no convincing scientific evidence that room air ionizers have any beneficial effects in allergic respiratory disorders.
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