Depending on who is asking, the question typically falls in one of two broad restoration categories:
Realizing that I'm no medical authority, I urge you to check out the following with a qualified medical or public health physician, or with the American Lung Association (www.LungUSA.org).
Let's start with a little background. Combustion smoke particles are measured in microns (1/1,000,000 of a meter or 1/25,000 of an inch). They generally range in size from 0.1 to 4 microns. When rendered airborne, particles in the 5-micron range remain airborne for some 20 minutes; 1-micron particles, for eight and a half hours; and those smaller than 1 micron remain airborne more or less permanently, according to Stanford Research Institute.
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 the bronchial passages leading down to our lungs. Cilia are hair-like structures that catch particles and push them back into the throat where they are expectorated (spit it 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 can potentially penetrate deep 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, enabling us to continue living for a few more minutes.
OK, lesson over.
So here's the point. At best, combustion smoke - any small particles, really - may cause irritation; at worst, they may scar tender lung tissues (alveoli) permanently, especially when inhaled 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 to1 microns) for 30 years and winds up with emphysema (if he or she manages to avoid the multiple Class A carcinogens contained in cigarette smoke, that is).
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). University of North Carolina 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."
Berry goes on to state: "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)," Berry states.
Certainly, when hazardous materials such as lead or asbestos are encountered during tear-out of unsalvageable fire-damaged materials, abatement procedures performed by qualified persons usually include the use of AFDs as required by OSHA.
The bottom line is, when workers are exposed to high concentrations of soot particles for prolonged periods at the outset of fire 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:
Certainly, HEPA-filtered AFDs, along with containment, are appropriate - usually mandatory - on mold and, especially, sewage losses, as an OSHA-preferred engineering control to effectively manage airflow and to prevent cross contamination (ref. pg. 31, "Microbial Contamination," IICRC S500 Standard and Reference Guide for Professional Water Damage Restoration). Again, personal protective equipment (PPE) is, according to OSHA, a secondary method for ensuring safety and health in contaminated situations. This point is elaborated upon in the IICRC S520 Standard and Reference Guide for Professional Mold Remediation in a number of places.
As far as the IICRC S500 goes, however, interested parties can refer to standard section 12.3.5 Containment, which states:
Precautions must be taken to minimize cross contamination from affected to unaffected areas by traffic or material handling. Shut down any air handling equipment and seal off supply and return registers. It is highly recommended that contaminated areas be contained with heavy-gauge polyethylene sheeting, often in combination with negative air pressure, to prevent cross contamination.
Cross contamination is the issue. There are several ways to create negative air pressure, including the use of vacuum equipment and exhaust fans. However, the most efficient and reliable way, especially for extended periods, is with the use of an AFD. Preferably it should be HEPA-filtered to prevent contaminating unaffected areas, even if outside the structure, that may be occupied by people, even if only passers-by.
Even on Category 1 water losses, AFDs may be appropriate during drying to capture soils that wick from carpet backings to the tips of yarns, only to be rendered airborne by the considerable air movement specified by the IICRC Applied Structural Drying (ASD) Technical Advisory Committee (TAC). The ASD TAC specification for initial air mover placement is one per 10 to 14 linear feet of wall area. This means that, in a 12-by-12-foot room, there may be as few as three or as many as five air movers, depending on the absorbency of materials present. At a minimum, three laminar airflow blowers will be generating a combined total of 3,400 cfm, while three axial blowers may generate some 5,400 to 9,000 cfm, depending on make and model.
Of course, the deciding factor is the health status of occupants. While not providing medical advice, technicians still can respond with sound professional judgment to customer-specified health conditions, such as pregnancy; occupancy by infants or elderly persons with under-developed or deteriorated immune systems; occupancy by those recovering from recent surgery or illness; occupancy by those on regimens of prescription drugs or chemotherapy, or by those who are respiratory impaired (e.g., emphysema, asthma). While water-restoration technicians and insurance professionals are encouraged to use common sense, occupants can verify the need for appropriate protective measures by consulting with personal or corporate physicians or qualified public health officials.
The objective is to avoid any instance, or even giving any impression, of occupants or workers being harmed in any way by the restoration process. If harm, or even the impression of harm, occurs, unnecessary delays or substantial increases in the scope or cost of the loss may follow; at worst, someone may decide to sue for personal injury. This falls under the proverbial, "an ounce of prevention is worth a pound of cure."
OK. While AFDs may not be needed on minor fire or many Category 1 water losses, their use may be prudent based on circumstances, occupants, and other factors that enter into professional judgment on other types of losses. There is no blanket rule to follow, but then, that's why we call ourselves professionals. Certainly, AFD cost considerations should never take precedence over human health.
The opinions and interpretations stated herein are my own and do not necessarily reflect the official position of the IICRC or any industry associations, their staffs or boards. I hope this helps.