Air Filtration Devices (AFDs) on Disaster Jobs
September 14, 2011
At least once a week, I get calls about the use of HEPA-rated (99.97% at 0.3 microns) air filtration devices, also known as AFDs, negative air machines (NAMs), or air scrubbers, on disaster restoration jobs.
Depending on who is asking, typically, my answer falls in one of two broad restoration categories:
- Use of AFDs on fire losses, or
- Use of AFDs on water losses, including Category 1 (clean source) water losses
Let’s start with a little background: Combustion smoke particles are measured in microns (1/1,000,000th of a meter or 1/25,400th of an inch). They generally range in size from 0.1 to 4 microns. According to Stanford Research Institute, when rendered airborne, particles in the five-micron range remain airborne for some 20 minutes, one micron particles for eight and one-half hours, and those smaller than one micron remain airborne more or less permanently.
Now, bear with me for a short lesson in physiology – don’t worry, you can handle it if I can.
The human respiratory system is able to filter particles from the air we breathe down to about 10 microns, thanks to the cilia in our bronchial passages leading down to the lungs. The cilia are hair-like structures that catch particles and push them back into the throat where they are expectorated (OK, spit out!) or swallowed and eliminated through the digestive tract. Many small particles are breathed in and out without being trapped within lung tissues. However, particles smaller than 10 microns potentially can penetrate deeply into lung tissues where some encounter the alveoli.
The alveoli are tender membranes that transfer oxygen from air breathed into the lung, to the blood circulating through capillaries surrounding the alveoli and eventually on to the heart. Blood becomes red when oxygen molecules attach to hemoglobin, an oxygen carrying protein in blood. The body’s heart, a rather efficient pump, pressurizes the blood and circulates oxygenated blood to all parts of the body, which process enables us to continue living for a few more minutes.
So here’s the point: at best, combustion smoke – really any small particles - may cause irritation; at worst, they may scar tender lung tissues (alveoli) permanently, especially when breathed in quantity or for prolonged periods. The end result may be permanent reduction in respiratory capacity. An exaggerated example of this process is the long-term smoker who inhales cigarette smoke (0.01-1 microns) for 30 years and winds up with emphysema – that is, if he or she manages to avoid the multiple Class A carcinogens contained in cigarette smoke.
Arguably, these particles may be covered under provisions in OSHA’s 29 CFR Part 1910, General Industry Standard, §1000 under “Air Contaminants.” Business owners may be required to provide measures to protect workers from them, should they become a targeted safety issue. If so, OSHA regulations always elevate engineering controls (e.g., HEPA-filtered AFD, containment) over personal protective equipment (e.g., respirators). UNC Professor of Public Health, Dr. Michael Berry, in his book “Protecting the Built Environment: Cleaning for Health,” characterizes “products of incomplete combustion” or “PICs” (fire soot components) as polynuclear aromatic hydrocarbons, or PAHs. According to Dr. Berry, combustion organics, often attached to particles, “. . . can affect health by causing cancer and cardiovascular problems and by irritating mucus membranes.” He goes on to say:
“Cancer is the most serious health consequence of inhaling combustion particles. The most common particle, soot, is itself carcinogenic. Soot particles, which contain PAHs, are adsorbed onto the surfaces of fine particles (less than 10 microns) which can be inhaled deeply into the lungs.
Particles can also add to the risk of cancer because of their size and shape rather than any carcinogenic properties. They can carry carcinogens whenever cancer-causing agents are adsorbed onto them. When carrier particles enter the lungs, the cancer-causing agent stays in contact with the cells of the lungs longer than it would otherwise as a gas. In some ways, the particles act like a time-release capsule. The composition of these cancer-causing agents, particles, and gases varies with fuel and burning conditions. Inhaled particles can also irritate respiratory tissue and the eyes. The severity of the irritation depends on the concentration of particles which depends in part on what the particle itself is made of – on its chemical species. Lung function decreases when respirable particles occur alone, along with gases, or in concentrations greater than 300 µg/m3 (micrograms per cubic meter).”
Certainly, when hazardous materials (HAZMAT), such as lead or asbestos, are encountered during tear-out of unsalvageable fire or water-damaged materials, abatement procedures performed by qualified persons usually include the use of AFDs, as required by OSHA.
The bottom line here is this: When workers are exposed to high concentrations of soot or demolition particles for prolonged periods at the outset of disaster processing, and especially during tear-out or pack-outs when these particles are repeatedly disturbed and suspended in respirable air, reasonable and prudent precautions may include:
- Ventilating the structure when practical, weather conditions and construction characteristics permitting;
- Containing areas of heaviest contamination (gutted rooms) with appropriate engineering controls (critical barriers; 6-mil poly, managed airflow);
- Using AFDs to filter respirable air when workers are exposed to HAZMAT or quantities of soot for extended periods, and especially, when ventilation is not practical (commercial buildings with sealed or no windows; basements; weather extremes);
- Providing workers with appropriate respiratory, eye and hand protection when processing quantities of soot-contaminated items or materials;
- Cleaning and protecting the HVAC system as soon as practical, typically after processing ceilings, walls, fixtures, contents and flooring.