White smoke occurs when something is burning and producing an incomplete combustion reaction. This means the fuel is not able to combust completely with oxygen, leaving behind unburnt fuel particles that give the smoke a white or grayish appearance. There are several common causes of white smoke from burning materials:
Wood
Fresh wood that is still somewhat green or wet tends to produce more white smoke when burned because the moisture prevents complete combustion. As the wood dries out and more water evaporates, it will begin to burn cleaner with less smoke. Softwoods like pine, cedar and spruce are more prone to creating white smoke than hardwoods like oak. The resin content also contributes to more smoke.
Wax and Paraffin
Candles contain wax or paraffin that melts and vaporizes when burned, producing clouds of white smoke before becoming fully combusted. This is why candle smoke appears whiter nearer the wick where temperatures are lower. Soy, beeswax and tallow candles tend to burn cleaner than paraffin. Votive and tea lights also generate more smoke than taller pillars or tapers.
Oil
Oily fuels like cooking oil, lamp oil and kerosene do not combust efficiently and leave behind unburnt carbon particles that show up as dense white smoke. This material can condense on surfaces as oily soot. Old or contaminated fuel creates even more smoke. The wick size also influences smoke levels, with larger wicks producing a smokier flame.
Rubber
The hydrocarbon polymers in rubber do not fully decompose when burned, releasing vaporized particles that emerge as thick white smoke. This applies to natural as well as synthetic rubber. Items containing rubber like tires, hoses and seals will emit pungent white smoke when burned due to the rubber additive chemicals as well.
Plastics
Like rubber, the complex hydrocarbons in plastics do not combust cleanly and completely. The burning plastic liquefies and creates smoke filled with tiny droplets of unburnt fuel. PVC plastic in particular produces heavy white smoke due to all the chlorine present. The smoke can also contain toxic chemicals depending on the plastic composition.
Grease Fires
Oil and fat based substances like lard, grease and butter are composed of long hydrocarbons that do not fully decompose during burning. This leads to thick clouds of white and gray smoke as the material releases vaporized grease into the air. Grease accumulation on grills, stoves and ovens can cause extreme levels of smoke when ignited.
Food Items
High fat foods with oils and greases like bacon, sausages, ribs and fried items will release large amounts of white smoke when cooked over an open flame or hot surface. Foods with sugars like cereals and breads will also burn with white smoke due to the charring of carbohydrates. Overcooked meats and burnt toast are examples of foods that commonly exhibit incomplete combustion.
Poor Combustion Conditions
Any fuel will burn with smokier, whiter emissions under conditions that prevent full combustion. Restricting airflow by burning material in an enclosed space hampers complete burning. Low heat and low oxygen environments also increase white smoke by not allowing the reactions to fully complete. This is why starting wood fires and grills produce more initial white smoke that lessens as the fire strengthens.
Ash and Mineral Deposits
As organic material burns, ash and mineral residues are left behind that can become airborne in the smoke. These powdery white particulates are a major component of smoke from burning vegetative matter like wood and dry leaves. Home heating systems and forest fires showcase these billowing white emissions laced with ash.
Paper
The primary component of paper is cellulose from wood pulp. When paper burns, the cellulose does not fully decompose, generating clouds of white smoke along with ash particles from additives used to manufacture the paper. Thick stacks of paper and cardboard boxes will exhibit incomplete combustion when burned.
Fabrics/Cotton
Plant-based fabrics like cotton and linen are made of cellulose that undergoes incomplete combustion, just like burning wood. Synthetic fabrics like polyester also release white smoke from the plastics within the material. The dyes, coatings and treatments used on fabrics further contribute to increased visible smoke.
Coal
While coal can burn quite cleanly, low grade and low heat coal combustion results in more unburnt fuel sent up the stack. This material condenses into white smoke laced with particulates. Coal fired power plants must maintain high temperatures and ample oxygen to prevent excess white smoke in the exhaust.
Tobacco Smoke
The incomplete combustion of tobacco in cigarettes, cigars and pipes produces the characteristic white/gray smoke as hot gases carrying particulates are exhaled or released into the air. Tobacco smoke is filled with tiny droplets of tars, resins and other byproducts that generate visible white emissions.
Engine Exhaust
The combustion inside engines is never 100% complete, so some amount of unburnt fuel, oil and particulates make their way into the exhaust as white smoke. Diesel engines are notorious for billowing white smoke when the engine is cold or malfunctioning. Steam vapor from the engine can also condense into white exhaust.
Fire Extinguishers
Dry chemical fire extinguishers release a white powder that can obscure vision similar to smoke. CO2 extinguishers also create a large white cloud due to the cold temperature of the carbon dioxide turning moisture in the air into fog. This simulated smoke can make it hard to see an active fire.
Mixture of Colors
Different sources of smoke mixing together can create the illusion of white smoke. Grayish blue smoke from materials like wood combined with small amounts of black smoke from plastics or oil can blend to appear white or very light gray. Multiple heat sources and fuels burning together muddle the smoke color.
Steam and Condensation
Water vapor from boiling or steaming materials can resemble white smoke. As this moisture contacts cooler air it rapidly condenses into fog-like droplets that take on a smoke-like appearance. Steam from cooling towers and stove vents are common examples of white emissions that are simply water condensation, not combustion.
Conclusion
White smoke requires an environment with incomplete combustion where unburnt fuel particles are released as vapors that condense into thick white emissions. This commonly occurs with materials like wood, wax, plastic, oil and grease that do not fully decompose when burned. Restricted oxygen, low heat, high moisture and dirty fuel sources also increase white smoke by preventing efficient burning conditions. Being aware of the causes of white smoke can help identify fire hazards, combustion issues and potential pollution sources.
