Science of Secondhand Smoke

The Science of Secondhand Smoke (SHS)

Bogus vs Real Science

And why HVAC engineers, industrial hygienists and environmental consultants are ill-informed about it.


* The visible plumes of smoke coming off the burning tip of a cigarette are just a tiny fraction of what is present in secondhand smoke. The rest is made up of invisible particles in the 0.2 to 0.4 micron range and gasses. (For size comparison, 25 microns = 1 mil or 0.001 inch.)

* Particles this small move primarily according to the laws of diffusion along the concentration gradient: from areas of high concentration to areas of low concentration.

* Typical flow rates provided by HVAC systems are insufficient to counter this basic diffusion movement of SHS.

* HVAC engineers are in the business of providing a comfortable indoor environment, not removing possible hazardous indoor air pollutants. Industrial hygienists and environmental consultants are usually untrained in the basic physics of secondhand smoke. They often fall prey to the “seeing is believing” syndrome.

* Federal agency guidelines are typically of no use since federal regulatory agencies, such as the U.S. EPA, are barred from issuing SHS regulations due to tobacco industry congressional lobbying.


When Heating, Ventilation & Air Conditioning (HVAC) engineers are consulted on providing ventilation solutions for secondhand smoke (SHS) their recommendations are invariably flawed and ineffective. The reasons are:

1) Comfort not health – Their aim is to provide a comfortable indoor environment, as defined by temperature and humidity, not a safe environment free of hazardous airborne pollutants.

2) Lack of scientific knowledge – They have no knowledge of the basic science underpinning the behavior of the bulk of what constitutes SHS. They believe instead, as do the general public, that SHS is solely the small fraction that is visible, wafted about by the slightest breeze.

For a true understanding, one must go to the landmark U.S. Surgeon General’s Report, The Health Consequences of Involuntary Smoking, published in 1986. On pages 137-139, the report discusses the research on the number and size distribution of particles in environmental tobacco smoke (ETS), an older name for SHS, and the laws governing its movement. On page 137, it states:
‘The mass median diameter of ETS is between appproximately 0.2 microns and 0.4 microns.’

Smoke Human Hair Comparison

Scanning electron micrograph of miniature glass beads produced by the University of Missouri-Rolla with human hair for size comparison Magnification 500x

To put this into perspective, look at the figure above, in which a human hair is shown magnified 500x alongside some miniature glass beads. The hair is about 0.004″ (4 thousandths inch or 4 mil) in diameter, or 100 microns, and the bottom glass bead is just over 40 microns (0.0016″ or 1.6 mil) in diameter. The small black spot on the top left bead is about 1 micron, or 2-1/2 times the diameter of the upper range of SHS particles.

It is frequently claimed that just providing a smoking room with an exhaust fan to maintain it at a negative pressure, and ducting the smoke-polluted air to the outside of the building, will prevent any tobacco smoke generated inside the room from migrating to adjoining areas. This simply isn’t true, due to the laws governing these invisible smoke constituents.

Turning again to the Surgeon General’s report, page 137:

‘ETS particles are in the diffusion-controlled regime for particle removal and therefore will tend to follow stream lines, remain airborne for long periods of time, and rapidly disperse through open volumes.’

Being in the diffusion-controlled regime for particle removal means the movement of SHS is determined mainly by the concentration gradient, SHS particles diffusing or moving from areas of high concentration to areas of low concentration. Providing a countervailing air flow (due to “negative pressure”) will have some effect but the primary mechanism remains diffusion.

This is illustrated in the figure below, showing in plan smoking room 4C in Lambert-St. Louis International Airport, St. Louis, Missouri, USA, which has been the subject of several tests by Missouri GASP. As shown, makeup air enters through the open doorway connecting the room to the adjoining “No Smoking” designated areas of the airport but this doesn’t prevent SHS diffusing out through the open doorway.
Lambert Smoking Room
This is one of seven smoking rooms constructed and opened by Lambert airport in 1997 rather than going smoke-free, as sought by Missouri GASP which had filed an Americans with Disabilities Act (ADA) complaint with the U.S. Department of Justice in 1994.

William Fronick, Lambert’s Director of Planning and Engineering, described the planned smoking rooms prior to their construction at an airport meeting with Missouri GASP president, Martin Pion, in April 1996. Pion argued that, based on his semiconductor physics expertise and knowledge overseeing semiconductor clean rooms at McDonnell Douglas Astronautics Co., the smoking room design would permit SHS to diffuse out through the open doorway. Fronick rejected this argument, saying he had designed hospital operating rooms which had to provide a germ-free environment, and he was confident the smoking rooms would work.

The dispute between Lambert and Missouri GASP over the smoking rooms was the subject of a St. Louis Post-Dispatch article by reporter Robert Manor, published February 3, 1997. The article, Where There’s Smoke: There’ll Soon Be A Lounge, At Lambert, reported the seven smoking rooms cost a total of $450,000. It included the following attribution to Fronick:

‘Fronic (sic) said some lounges were recently opened to the public and seem to be working well.

“You could see the blue haze inside, but nothing came out the door,” he said. “We assume if you can’t see it, it’s not there.”

The same article reported an interview with Pion, in which he said the airport was headed in the right direction in 1994 [when it was considering going smokefree] and is wasting money on smoking lounges that won’t protect people with respiratory problems.

‘Pion oversaw a suite of clean rooms at McDonnell Douglas Corp. and is familiar with techniques for eliminating pollution from the atmosphere. Clean Rooms keep environmental contaminants out of the atmosphere, and Pion says the same principle applies to smoking lounges.

“A smoking room is a clean room in reverse,” he said. “You are trying to keep the pollutants and carcinogens in. You have to have an air lock,” he said. “You have to monitor the air pressure [differentials] carefully.”

Pion said that for the smoking lounges to work, they would need to be isolated from the airport by a double-doored air lock and a separate ventilation system to draw air from the outside, circulate it through the room and then exhaust it back outside.’

The environmental consulting firm McCoy and McCoy Inc. (MMI), St. Louis, performed air sampling tests for Lambert airport on the smoking rooms shortly after they opened in early 1997. The measurements were primarily to determine airflow rates through the open doorway into each room, and the velocity of exhaust air to ensure compliance with the American National Standards Institute/American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (ANSI/ASHRAE) Standard 62-1989, 62a-1990, Ventilation for Acceptable Indoor Air Quality.

(Note: The tobacco industry is known to have coerced and manipulated ASHRAE to ensure these standards permit a moderate amount of smoking in setting ventilation rates in public buildings and workplaces (which includes airports). The latest ASHRAE Standard 62-1999, which supersedes the above, is based on the assumption that such venues be smoke-free, citing the scientific consensus that SHS is harmful to human health.)

In a cover letter dated February 27, 1997, accompanying the MMI report to the airport Carol H. Byington, PhD, wrote:

‘A negative pressure in each of the rooms would assure that the smoke generated inside the lounges would not migrate or vent into the outer concourse areas.’

In October 1997, Missouri GASP wrote to then airport director, Col. Leonard Griggs, asking for airport approval to scientifically test Fronick’s assertion that the smoking rooms were 100% effective. The method proposed was to use a static nicotine monitor either worn by an airport employee or hidden from view near a smoking lounge. In a reply dated October 28, 1997, Griggs replied:

‘Thank you for your concern and generous offer to test the presence of nicotine vapor in the air. However, I cannot accept your offer. Thank you again for your interest.’

Faced with the airport’s non-cooperation Missouri GASP sought help from TWA non-smoking gate employees and found one working in a gate area in Lambert concourse C near a smoking room. She wore a nicotine monitor while working in the gate area for 137 hours. A non-smoking bar employee working in Seattle-Tacoma International Airport, which was totally smoke-free indoors but allowed smoking around entrances, conducted a similar nicotine test for Missouri GASP for comparison. Both nicotine monitors were analyzed by a laboratory at the University of California, Berkeley, and indicated that not only was there a significant amount of nicotine vapor in the gate area in Lambert near the smoking room but that approximately 70-80% was due to secondhand smoke escaping from the nearby smoking room, the rest originating from smoking around entrances and possible illicit smoking.

Based on the risk assessments of Repace & Lowry, who calculated lung cancer risks from secondhand smoke exposure

An employee working in a gate area adjoining the smoking room and wearing a static nicotine monitor for 137 hours while at the gate was exposed to an average 0.44 µg/cu. m. of nicotine vapor. This corresponds to an elevated cancer risk estimated as nearly 60 times the limit allowed for other federally regulated human carcinogens.

According to James Repace, 0.75 µg/cu m of respirable suspended particulates, which give rise to a lifetime lung cancer risk of 10 per million exposed population, corresponds approximately to a nicotine concentration of 0.075 µg/cu m.

Hence, the lifetime lung cancer risk for each airport is:

Seattle-TAC (1998): 10 x 0.15/0.075 = 20 per million

Lambert (1998): 10 x 0.44/0.075 = 60 per million.

Lambert (2002): 10 x 0.7/0.075 = 90 per million.

Repace, in reviewing the earlier results, pointed out that the California EPA had concluded that ETS caused 3,000 annual lung cancer deaths among nonsmokers and between 35,000-62,000 deaths due to heart disease. This means ETS is 10-20 times more deadly for heart disease mortality, so the mortality for this disease, based on the above results, would be:

SETAC : 200-400 deaths per million;

Lambert: 600-1200 (1998) or 900-1800 (2002) deaths per million.

These results

When questioned about the smoking rooms during an interview by a TV reporter in July 1998, William Fronick, Lambert’s Director of Planning and Engineering, said the air ducts in the ceiling suck up 100% of the smoke and send it outdoors.

Fronick: “The air is always trying to get in from the outside, not trying to get out from the inside.”

Not just HVAC engineers but also environmental consultants claim that purely maintaining a smoking room at negative pressure with respect to adjoining areas will ensure 100% effectiveness at trapping the smoke inside.

p 181 on “retention” Particles in this size range are like weaponized anthrax: when a person inhales them they go deep into the lungs where they remain for long periods doing serious damage.