How Smoke Is Made

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19th Mar 2019

How is Smoke Made?

If you light a fire or a cigarette, you'll probably see smoke rise. Smoke results from the burning or decomposition in high temperatures of matter. It forms from the combination of airborne solid and liquid particulates and gases in the surrounding air. You might define smoke as an aerosol that consists of airborne solids and liquid particles.

Smoke is an unintentional byproduct of starting fires, recreational smoking, and cooking, but it is also employed deliberately for pest control, as in fumigation; for military offense and defense, as with smoke screens; in rituals that involve burning incense and spices; and for flavor and preservation in food preparation.

Smoke From Fires

What Is Smoke?

Smoke is made from incomplete combustion, which is combustion that occurs when there's not enough oxygen available to completely burn up all of the fuel. The unburned material combines with carbon dioxide and water vapor produced in the burning process to create smoke. Most of what is visible in smoke consists of carbon, or soot, but smoke also often contains carbon monoxide and a variety of potentially carcinogenic chemical compounds. The exact chemicals produced depend on the fuel and conditions.

Different Types of Smoke

Smoke comes in three primary types: wet, dry, and protein. Fine powder typically characterizes dry smoke, which results from high-heat, fast burning of wood or paper. Wet smoke, a byproduct of low-heat, slow burning of plastics and rubber, has a thick composition that leaves a sticky, odorous residue. Protein smoke leaves a nearly invisible, strong-smelling residue after the slow burning of organic materials such as food.

Firefighters assess different attributes of smoke to help them understand the characteristics of a fire and where it might spread. These include its volume, velocity, density, and color. For instance, the color of smoke often changes depending on how long the fire has been burning and what its fuel is.

Soot and Protein Smoke

Dangers of Smoke

Even before considering the harmful chemicals that incomplete combustion lends to smoke, the suspension itself presents dangers. The leading cause of deaths from in-home fires is not the fire itself but inhalation of smoke from the fire, as the exposure to hot gasses damages the respiratory system. Statistics attribute 50 to 80 percent of fire deaths to smoke inhalation.

Particulate matter in smoke not only reduces visibility, but it also presents a health hazard because these particles are small enough to easily inhale into the body, where they can settle deep in the lungs. These irritants cause breathing problems, lung dysfunction, inflammation, and cardiovascular difficulties.

Carbon monoxide is a chemical asphyxiant that can prevent the transportation of oxygen in the body. It lacks color and odor, so carbon monoxide poisoning can quickly overcome someone without warning. While carbon monoxide is usually not present in smoke in high enough quantities to endanger the general population, those who endure long exposure or are very close to the smoke and those with already compromised health, such as those with cardiovascular and respiratory issues, are at a greater risk for complications.

Other compounds in smoke, like sulfur oxides, can form acids that can corrode the lungs, metal, and other materials.

The dangers of smoke are magnified for smokers and tobacco users. The U.S. Department of Health and Human Services estimates that of the more than 7,000 chemicals in cigarette smoke, around 70 are carcinogens. Among the identified chemicals are ammonia, cyanide, and formaldehyde. Cigarette smoke also damages blood vessels and inflames the lungs, which affects circulation of blood and oxygen through the body. Over time, the particles from this smoke accumulate in the esophagus and the lungs, and the chemicals from cigarette smoke get into the bloodstream to harm every part of the body. These effects extend even to nonsmokers through secondhand smoke.

For smokers who want to stop smoking, a popular alternative is vaping, which uses a device called a vape mod or vape pen to produce an inhalable vapor instead of smoke. This avoids some of the particulates present in cigarette smoke.

Smoke Corrosion

Once a fire has ended and the area cools down, the residue of smoke settles on surfaces, and the chemicals in this residue can corrode the material. When combined with humidity or moisture, the corrosion occurs more rapidly. It does not discriminate among materials, affecting metal, glass, and plastic, but the concern is highest for metals, especially electronics. A quick and thorough cleanup after exposure to smoke, whether from a cigarette or a wildfire, is crucial to reduce the potential damage to equipment and goods.

Measuring Smoke

Researchers have developed a number of methods to measure the density and volume of smoke. Among them is in-line capture, wherein a sample is sucked into a filter and its weight is taken before and after the test; and the filter/dilution tunnel, wherein a sample of smoke diluted with air is weighed.

To measure the opacity of smoke, measures like optical scattering and optical obscuration are used. In both methods, a beam of light is shot through a screen of smoke and a light detector determines the concentration of the smoke based on the amount of light that is reflected or passes through.

Another measure of smoke density, which is simpler though arguably less reliable, is the Ringelmann Smoke Chart, which consists of a series of six cards, one blank and the other five covered in grids of black lines with increasing thicknesses. A trained user can hold the cards at eye level so that the lines appear gray, look from the cards to the smoke, and match the color of the smoke to the appropriate card number to determine the smoke's density.

Medicinal Smoke

While numerous studies have documented its harms, a look back at history and assessment of current research suggest that some smoke has medicinal merit. For example, the ancient practice of burning herbs, called smudging, serves as a strong antiseptic. In one study, burning wood and a mixture of herbs in a closed room for one hour reduced the aerial bacteria in the room by about 95 percent.

Smoke can also be an effective and inexpensive way to get medicinal substances into the body. For instance, the medical use of marijuana has been used to treat many conditions, including Alzheimer's, mental conditions, and muscle spasms; to reduce anxiety, inflammation, and muscle tightness; and to stimulate appetite.

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