HEPA Purifiers
HEPA (high efficiency particulate air) filtration plays an important role in improving indoor air quality in both the domestic and the industrial setting. It works by trapping airborne particles such as house dust mite allergen, pollen grains, and cigarette smoke, on a filter made of glass fibres. The HEPA filter is found in both fitted installations that combine ventilation, heating and air conditioning, and in portable air purifiers. It is not the only type of air purifier – there are electrostatic and ultra-violet light systems as well, which work in a different way. However, the Environmental Protection Agency has said that a HEPA filter is the most effective way of dealing with airborne particles.
Top IQAir Air Purifier Models:
IQAir HeathPro 250
The IQAir HeathPro 250 is IQAir's "Allergy and Asthma Specialist", as well as the room air purifier with the highest filtration efficiency. It's mechanical HEPA filtration technology removes more particulate and molecular air pollution then any other domestic air purifier.
IQAir HP 250
IQAir HeathPro 150
The IQAir HealthPro 150 is the "compact" version of the IQAir HealthPro 250. It features the same fantastic filtration rate as the Health Pro 250, but is a bit shorter. The HealthPro 150 is thus an especially good choice for small rooms or offices.
IQAir HP 150
IQAir Allergen 100
The IQAir Allergen 100 offers ultra high-performance particle control for allergy sufferers in a compact design. It has the same advanced micro- and nano-particle filter technologies as the HealthPro models, but in a smaller housing and without gas and odour filtration.
IQAir Allergen 100
IQAir GC MultiGas
IQAir GC MultiGas air purifier is the best air cleaner for people suffering from multiple chemical sensitivity (MCS). This air cleaner filters the air for a wide spectrum of chemical and odorous pollution. The IQAir GC MultiGas removes chemical as well as particulate air pollution in residential, professional, as well as commercial settings.
IQAir GC MultiGas
FAQ about HEPA Purifiers :
- What is a HEPA air purifier?
- How long have HEPA air purifiers been around?
- How does a HEPA air purifier work?
- What does a HEPA air purifier take out of the air?
- How is the performance of a HEPA air purifier judged?
- What are the possible limitations of a HEPA filter?
- Is there any evidence that the presence of a HEPA filter improves health?
- What are the main applications of a HEPA air purifier?
- What is the difference between a HEPA and a HyperHEPA air purifier?
What is a HEPA air purifier?
HEPA stands for High Efficiency Particulate Air and HEPA filters are a component of many types of mechanical air purifier. They may be combined with other elements, such as gas absorbing filters or microorganism destruction systems. A HEPA filter actually consists of a web of glass fibres capable of trapping particles of a range of sizes.
A true HEPA filter meets specifications of the United States Department of Energy for DOE regulated applications. Air purifiers labelled ‘HEPA-type’, ‘HEPA-like’ or even ‘99%-HEPA’ will not necessarily meet the same performance standards. A true HEPA filter has to be able to remove 99.97% of airborne particles of size 0.3 micrometers diameter passing through it. It can, of course, remove particles bigger and smaller than this, but it is the 0.3 micrometer particles that are hardest to trap in the filter, so that is why these are the particles used to judge performance.
How long have HEPA air purifiers been around?
It was during the late 1940s that the United States Army Chemical Corps and the United States Atomic Energy Commission developed the first HEPA filters, in order to protect against the spread of radioactive dust during research on the atom bomb. These early HEPA filters were rigid and unwieldy machines, quite unlike their modern counterparts. They actually contained asbestos imported from Africa or Bolivia. Concern over the health impact of asbestos led to the development of alternative materials. There were also concerns about leaks and defects in the filter so, again, research was needed into a better filter material.
During the development of the atom bomb, HEPA technology was considered ‘top secret’ but, after the war, the government declassified the technology so it could be used in commercial and residential settings, as it is today.
How does a HEPA air purifier work?
The HEPA is a specialized filter consisting of a folded mat of microscopic borosilicate glass fibres. It has three different modes of action, each of which acts best upon a different size of particle. Interception deals with particles above 0.4 microns in size and involves the particle sticking to a fibre in the HEPA filter when it comes close to it. In impaction, which also mainly affects particles above 0.4 microns, the particle is blown towards the fibres by the airstream on which it is travelling. It then collides with the fibres and sticks fast to them. Finally there is diffusion, which mainly affects smaller particles, of size below 0.1 microns. The particle collides with air molecules which throw it off course. Diffusion keeps the particle within the filter until it is captured by impaction or interception.
What of particles between this size range? They are captured, but not as efficiently. The 0.3 micron 'window' is known as the most penetrating particle size (MPPS), because particles in this size range penetrate further into the mesh before being trapped than do smaller and larger particles. In fact, the ability of HEPA filters to capture particles of size 0.3 microns is actually used as a measure of its effectiveness. The DOP penetration test involves sending a test stream of particles of this size through the filter and using a particle counter to measure the particles in the ingoing stream and outgoing stream to see what proportion is removed by the filter.
What does a HEPA air purifier take out of the air?
A HEPA air purifier will remove airborne particles over a wide size range. Examples include:
- Fungal spores – 100-2 microns
- Pollen grains – 100-0.25 microns
- House dust mite allergen – 25-0.1 microns
- Bacteria 25 – 0.25 microns
- Pet dander 10-0.1 microns
- Toner dust 10-0.1 microns
- PM10 – 10 microns or less (PM = particulate matter)
- Tobacco smoke 4-0.01 microns
- PM2.5 – 2.5 microns or less
- Viruses – 0.05-0.003 microns
- Ultrafine particles – 0.1 to 0.001 microns.
How is the performance of a HEPA air purifier judged?
First, be aware that efficiency and effectiveness, although they sound similar, are not the same thing when it comes to choosing a HEPA air purifier. Efficiency is usually given as a percentage and it is a measure of the ability of the air purifier to remove particles from the air passing through it. The effectiveness is a measure of the air purifier's ability to reduce airborne particles in an occupied room.
Efficiency depends on both airflow rate through the purifier and on the particulate load.
Effectiveness depends upon: efficiency, the amount of air being filtered, and the path the clean air follows after leaving the filter.
So a highly efficient filter could actually be quite ineffective if the amount of air it has to filter is large and the airflow rate low.
A number of methods have been developed to determine the efficiency of HEPA filters installed in heating, ventilation, and air conditioning (HVAC) but these are not necessarily applicable to HEPA filters in portable air cleaners.
There is a measure that has been developed by the Association of Home Appliance Manufacturers called the Clean Air Delivery Rate (CADR). Important to note here is that this is the association of manufactureres that have come together to develop a standart to test their own products - so by far not an independent standard at all. Eventhough CADR is used by the Environmental Protection Agency and the Consumers Union to compare air purifiers. It gives measures only for dust, tobacco smoke, and pollen removal. CADR does not give you any information about the long-term performance of the air purifier.
Tests can also be done using a particle counter, which is a laser-based device that can detect the density of particles in a room. Such tests are an accurate way of measuring the impact that an air purifier has on a room's air quality.
What are the possible limitations of a HEPA filter?
An air purifier fitted with a HEPA filter will only remove airborne particle. It will not remove gaseous pollution, like volatile organic compounds, or settled particles or dust. So, for instance, a HEPA filter will not be able to remove house dust mite allergen that is present in carpets, bedding and soft furnishings will remain unaffected. To remove gaseous pollution you would need a system that also incorporates activated carbon which will absorb gases.
Is there any evidence that the presence of a HEPA filter improves health?
The effects of particle air cleaners on allergy and asthma symptoms were reviewed some time ago by the Institute of Medicine (IOM) Committee on the Assessment of Asthma and Indoor Air of the National Academy of Sciences. They said:
'The results of existing experimental studies are inadequate to draw firm conclusions regarding the benefits of air cleaning for asthmatic and allergic individuals…. Air cleaners are helpful in some situations in reducing allergy or asthma symptoms, particularly seasonal symptoms, but it is clear that air cleaning, as applied in the studies, is not consistently and highly effective in reducing symptoms.'
The problem is that while it is easy to prove that a HEPA filter will reduce airborne particulate pollution, if it is a good model operating well, it is far more challenging to prove positive benefits to health. Nevertheless, clinical studies do appear from time to time. Here are a few examples:
- Part of the Cincinnati Asthma Prevention Study showed that kids with asthma who were exposed to second hand smoke benefited from the presence of a HEPA air purifier in their bedroom. Having a real HEPA filter installed led to a nearly 20% reduction in unscheduled asthma visits to the hospital.
- A recent study from researchers at Simon Fraser University, Burnaby, Canada, reveals how a HEPA filter both cuts PM-based indoor pollution and improves two significant markers for heart health. Forty five healthy adults took part and their homes were monitored for two consecutive seven-day periods. During this time, one HEPA (Honeywell Model 50300) was placed in the main room and a quieter HEPA filter (Honeywell Model 18150) in the participant’s bedroom. During one seven day period, the HEPA filters were operated normally and during the other they were operated without the filters. Levels of C-reactive protein (CRP), a marker for inflammation and heart disease went down 33% with use of the HEPA filter.
- A study from Singapore General Hospital showed that installation of HEPA filters reduced the number of cases of invasive aspergillosis, a potentially fatal fungal infection, by 50%.
What are the main applications of a HEPA air purifier?
Modern HEPA air purifiers are used in hospitals and in the aerospace, electronics, and pharmaceutical industries. The filter may be combined with an ultraviolet light device to assist the removal of bacteria and viruses in a healthcare setting. In the home, portable air purifiers and vacuum cleaners fitted with HEPA filters can be used to remove dust containing house dust mites and pet dander which might otherwise provoke asthma or allergy symptoms.
What is the difference between a HEPA and a HyperHEPA air purifier?
The IQAir HyperHEPA® filter can remove particles down to 0.003 microns in size with a guaranteed efficiency of more than 99.5%. This is 100 times smaller than the lower limit of other HEPA air purifiers and 10 times smaller than a virus. The significance is that the HyperHEPA filter operates on the nanoscale, dealing with the ultrafine particles which other air purifiers cannot remove. The smaller the particle, the further it can penetrate into the body and therefore the greater the potential health risk. The performance of the HyperHEPA can also help create the ultra-clean environments required in certain industry sectors.
Further Information
EPA guide to residential air cleaners http://www.epa.gov/iaq/pubs/residair.html
Clearing the Air: Asthma and Indoor Air Exposures. Committee on the Assessment of Asthma and Indoor Air, Division of Health Promotion and Disease Prevention, Institute of Medicine. 2000. http://aspe.hhs.gov/sp/asthma/appxh.pdf
