Environmental Products Division
Biological, Chemical and Nuclear Hazards
FAQs Anthrax and HVAC Filtration
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What is anthrax?
Bacillus anthracis, commonly referred to as anthrax, is a bacteria that is spread by spores of the bacteria. The spore is typically in the 1 to 5 micron size range. The most common form of Anthrax is cutaneous, which is caused by the spore coming in contact with an open wound. Another far more potent form of the disease is inhalation anthrax, which is caused by breathing the spores.
How can anthrax be spread through the HVAC system?
There are several potential means of distributing the anthrax spores through the HVAC system. These include:
- Releasing spores at the air intake for the HVAC system, which may be easily accessed from outside of the building.
- Releasing spores from inside the building, near an intake for re-circulating air.
- Gaining access to the HVAC system, and releasing spores directly into the air-stream.
Can air filters be a viable means of capturing anthrax spores?
Since the anthrax spore is relatively large in size (1-5 microns), selecting the correct filters can provide a high collection efficiency in removing the spores from the air-stream. In addition to selecting the correct filter, it is also important that the HVAC system be in proper operating condition, including having the frames/filters properly sealed and having the fan sized to handle the resistance of the filters.
What filters are recommended for collection of particulate in the size range of anthrax spores? Are HEPA filters required?
While HEPA filters offer the optimum level of filtration for this particle size range, most HVAC systems are not built to handle the high airflow resistance of HEPA filters. High collection efficiencies can be expected from filters other than HEPAs, and at a resistance that can be handled by most HVAC systems. Following is a list of AAF filters, along with their minimum efficiency on 1.0 to 1.3 micron particles and their initial resistance, all at 500 fpm. For the maximum level of filtration, you should use the highest efficiency filter that your HVAC system can handle.
|
AAF Filter |
Filter Efficiency on 1.0 to 1.3 micron particles |
Initial Resistance @ 500 fpm |
| AstroCel HCX (HEPA) |
99.97%+ |
1.40" |
| BioCel (95% DOP) |
99+% |
0.95" |
| 90 95% VariCel |
98% |
0.58" |
| VariCel V MERV 15 |
97% |
0.59" |
In addition to the filters listed above, following are some additional filters and their efficiency on 1.0 to 1.3 micron particles. These filters are not recommended for use as the final filter for biological contaminants, but may be used in other applications or as prefilters.
|
AAF Filter |
Filter Efficiency on 1.0 to 1.3 micron particles |
Initial Resistance @ 500 fpm |
| 90 95% DriPak 2000 |
99% |
0.38" |
| 80 85% DriPak 2000 |
92% |
0.32" |
| 60 65% VariCel II |
50% |
0.40" |
| 40 45% DriPak 2000 |
48% |
0.21" |
| AmAir 62Plus |
42% |
0.42" |
| PerfectPleat Premium |
33% |
0.28" |
Why are pocket filters not recommended?
Pocket filters are an excellent choice in many applications, but in critical applications such as ones involving public health, the rigid box filters are preferred. The construction of the pocket filters is not as sturdy or rigid as box filters. Also, while the pocket filters will meet their rated efficiency over the life of the filter, under certain conditions, the efficiency of the pocket filters can drop below their initial levels. The paper media used in box filters maintain their initial efficiencies and actually grow more efficient as they load with dirt. Finally, when changing and disposing of the filters, the box filters encapsulate the captured particles within the filter cartridge much better than the pocket filters, making re-intrainment of the captured particles into the airstream less probable.
Is the INTERSEPT Antimicrobial effective against anthrax?
Because of the hazard involved in handling the anthrax bacteria, INTERSEPT has not been tested for efficacy against it. However, the anthrax bacterium is a gram-positive bacteria and INTERSEPT has proven effective in inhibiting the growth of similar gram-positive bacteria.
In addition to upgrading air filter efficiency, what else can be done to maximize the level of filtration in the HVAC system?
When upgrading the efficiency of your air filters, there are several considerations that should be made;
- If you are using holding frames, verify that at least 4 latches are used per filter, and that the latches are strong enough to provide a leak-free seal between the filter and frame.
- Verify that the frames have enough integrity to match the filter and the higher resistance of the filter, and that the frames are caulked/sealed around the perimeter to eliminate any leaks.
- If the holding frames have an old gasket, remove the gasket and purchase filters with a pre-applied gasketing.
- Verify that the HVAC system can tolerate the added resistance, without compromising airflow throughout the building.
- Develop and follow a routine maintenance program, including duct cleaning, coil cleaning, etc...
I really want HEPA-level filtration, but my system cant be modified. Do I have any options?
Yes, in fact you do. AAF markets a line of hospital-grade, high capacity HEPA-level air cleaning systems that provide the highest level of filtration. These systems can be portable or can be permanently installed. In addition, we have developed an application of these products to provide positive pressure ventilation for building occupants that would effectively isolate them from outside airborne threats. The so-called "Safe Rooms" can be set up in offices, in schools even in homes, and would ensure that only HEPA-filtered air is supplied to selected rooms within a building. Contact AAF directly for further information on these products.