HEPA and ULPA Filters

HEPA and ULPA Filters are two components of our NBC filtration system. Many air filtration systems use HEPA and ULPA Filters as a stand alone filtration system. Rising S Bunkers uses HEPA & ULPA Filters along with TEDA carbon to create the best solution for your NBC filtration needs.

Cutting Edge NBC Air Filtration Solutions


HEPA stands for High Efficiency Particulate Air filter. A HEPA filter is a type of air filter meeting certain standards of efficiency such as those set by the United States Department of Energy. To qualify as HEPA by US government standards, an air filter must remove (from the air that passes through) 99.97% of particles that have a size of 0.3 micrometres. (American Society of Mechanical Engineers, ASME AG-1a–2004, “Addenda to ASME AG-1–2003 Code on Nuclear Air and Gas Treatment”, 2004)

HEPA filters are composed of a mat of randomly arranged fibers. The fibers are typically composed of fiberglass and possess diameters between 0.5 and 2.0 micrometers. Key factors affecting function are fiber diameter, filter thickness, and face velocity. The air space between HEPA filter fibers is much greater than 0.3 μm. The common assumption that a HEPA filter acts like a sieve where particles smaller than the largest opening can pass through is incorrect. Unlike membrane filters at this pore size, where particles as wide as the largest opening or distance between fibers cannot pass in between them at all, HEPA filters are designed to target much smaller pollutants and particles. These particles are trapped (they stick to a fiber) through a combination of the following three mechanisms:

1. Interception, where particles following a line of flow in the air stream come within one radius of a fiber and adhere to it.

2. Impaction, where larger particles are unable to avoid fibers by following the curving contours of the air stream and are forced to embed in one of them directly; this effect increases with diminishing fiber separation and higher air flow velocity.

3. Diffusion, an enhancing mechanism that is a result of the collision with gas molecules by the smallest particles, especially those below 0.1 µm in diameter, which are thereby impeded and delayed in their path through the filter; this behavior is similar to Brownian motion and raises the probability that a particle will be stopped by either of the two mechanisms above; it becomes dominant at lower air flow velocities. Diffusion predominates below the 0.1 μm diameter particle size. Impaction and interception predominate above 0.4 μm. In between, near the most penetrating particle size (MPPS) 0.3 μm, both diffusion and interception are comparatively inefficient. Because this is the weakest point in the filter’s performance, the HEPA specifications use the retention of these particles to classify the filter.


Lastly, it is important to note that HEPA filters are designed to arrest very fine particles effectively, but they do not filter out gasses and odor molecules. Circumstances requiring filtration of volatile organic compounds, chemical vapors, cigarette, pet, and/or flatulence odors call for the use of an activated carbon (charcoal) filter instead of or in addition to a HEPA filter.



ULPA is an acronym for “ultra-low penetration air” Or “ultra-low particulate air”. A ULPA filter can remove from the air at least 99.999% of dust, pollen, mold, bacteria and any airborne particles with a size of 120 nanometres (0.12 micron) or larger. Even anthrax (which has one of the smallest particulates among the toxins) can’t pass through a ULPA filter.



Anthrax attacks - cleaning

The 2001 anthrax attacks in the United States, also known as Amerithrax from its Federal Bureau of Investigation (FBI) case name, occurred over the course of several weeks beginning on Tuesday, September 18, 2001, one week after the September 11 attacks. Letters containing anthrax spores were mailed to several news media offices and two Democratic U.S. Senators, killing five people and infecting 17 others. According to the FBI, the ensuing investigation became “one of the largest and most complex in the history of law enforcement”.

Anthrax is an acute disease caused by the bacterium Bacillus Anthracis.
Thousands of anthrax spores are required for human infection, of which all can fit in the area of a single pinhead.

Anthrax spores can be produced in vitro and used as a biological weapon. Anthrax does not spread directly from one infected animal or person to another; it is spread by spores. These spores can be transported by clothing or shoes. The body of an animal that had active anthrax at the time of death can also be a source of anthrax spores.

Until the twentieth century, anthrax infections killed hundreds of thousands of animals and people worldwide each year. French scientist Louis Pasteur developed the first effective vaccine for anthrax in 1881. Thanks to over a century of animal vaccination programs, sterilization of raw animal waste materials, and anthrax eradication programs in North America, Australia, New Zealand, Russia, Europe, and parts of Africa and Asia, anthrax infection is now relatively rare in domestic animals (with only a few dozen cases reported each year). Anthrax is especially rare in dogs and cats, as is evidenced by a single reported case in the USA in 2001.

Anthrax typically does not cause disease in carnivores and scavengers, even when these animals consume anthrax-infected carcasses. Anthrax outbreaks do occur in some wild animal populations with some regularity. The disease is more common in countries without widespread veterinary or human public health programs. In the 21st century, anthrax is still a problem in less developed countries. An outbreak of anthrax in humans who had eaten meat from a dead caribou was reported in Cagayan province in the Philippines in early 2010, with over 400 cases of illness and at least two fatalities.

Bacillus anthracis bacterial spores are soil-borne. Because of their long lifespan, spores are present globally and remain at the burial sites of animals killed by anthrax for many decades. Disturbed grave sites of infected animals have caused reinfection over 70 years after the animal’s interment.

HEPA & ULPA Filters are some of the best components for creating an effective NBC filtration system. Along with using TEDA carbon technology, NBC Filtrations System from Rising S Bunkers has a quality that cannot be beat.

 Learn why RSC uses activated TEDA carbon in all of out air filtration units – CLICK HERE 

Take a look inside the RSC Air Filtration Unit – See diagram – CLICK HERE