Smoke is the primary cause of fatalities during building fires, not the flames themselves. Scientific studies, historical data, and survivor testimonies all confirm this fact. Understanding the specific dangers of smoke is key to improving safety in fire emergencies.

Smoke presents several life-threatening dangers during building fires. Toxic gases, such as carbon monoxide, can cause poisoning, while intense heat can lead to burns and heat exhaustion. Smoke also reduces visibility, making evacuation difficult, and its rapid spread can quickly overwhelm escape routes, trapping occupants.

This article delves into the specific dangers of smoke, providing a deeper understanding of how it poses a threat during building fires.

Toxic Gases from Smoke in Building Fires

When a building is engulfed in smoke, three primary gas phenomena typically occur:

1. Release of Carbon Monoxide (CO): CO is a deadly gas that can cause poisoning, leading to unconsciousness or death in a short time.
2. Increase in Carbon Dioxide (CO2): Elevated CO2 levels trigger hyperventilation, causing people to inhale smoke more rapidly, which increases exposure to other toxic gases.
3. Decrease in Oxygen (O2): As O2 levels drop, suffocation and hyperventilation can occur, causing severe physical stress and potentially fatal outcomes.

Beyond these common gases, smoke may contain other harmful chemicals, depending on the materials that are burning. For instance, plastics and synthetic materials release highly toxic substances like cyanide. Even after a fire is extinguished, toxins remain embedded in walls, floors, and furniture, posing ongoing risks when touched or inhaled. This is why restoration workers and investigators wear personal protective equipment (PPE) on fire sites.

Carbon Monoxide Poisoning from Smoke in Building Fires

According to the ASHRAE Handbook of Smoke Control Engineering, carbon monoxide poisoning is the leading cause of death in building fires. CO can be lethal within just 5 minutes at high concentrations (Greiner, 2017).

Biologically, CO exposure increases carboxyhemoglobin (COHb) levels in the bloodstream, which severely reduces the blood’s ability to transport oxygen (O2) throughout the body, leading to oxygen deprivation in vital organs. Symptoms of CO poisoning can range from vomiting, unconsciousness, and brain damage to more severe outcomes such as heart irregularities, breathing difficulties, muscle weakness, and even miscarriages.

Extreme Heat from Smoke in Building Fires

Smoke doesn’t just pose respiratory dangers—it can also cause severe burns and heat-related illnesses. If the temperature of the smoke exceeds 250 °F (121 °C), it can burn human skin and airways within 10 minutes. Even at lower temperatures, prolonged exposure to smoke, ranging from 10 to 60 minutes, can cause heat stroke.

The clothing a person is wearing during a fire can either help or harm them. Clothes provide some insulation against direct burns, but they can also trap heat, hastening the onset of heat stroke by making the body feel hotter. Thus, while protective in some ways, clothing can also contribute to heat-related injuries in smoke-filled environments.

Reduced Visibility from Smoke in Building Fires

Smoke reduces visibility in fires, making it difficult for both occupants and rescuers to navigate safely. It does this in two ways:

1. Blocking Light: The particulates in smoke physically block light, preventing occupants from seeing their surroundings.
2. Eye Irritation: Smoke irritates the eyes, making it difficult for people to keep their eyes open, which further reduces their ability to see.

According to the ASHRAE Handbook of Smoke Control Engineering, reduced visibility is one of the most immediate threats during a fire because it slows down evacuation and rescue efforts. When visibility is compromised, occupants may struggle to find exits, leading to prolonged exposure to toxic smoke and heat. In extreme cases, low visibility can result in fatal falls from balconies, stairs, or ledges as people attempt to escape.

This is why exit signs are designed with illuminated LED lights—to help guide people through smoke-obscured spaces in emergencies.

Speedy Movement and Expansion of Smoke During Building Fires

One of the most dangerous features of smoke is how quickly it spreads. Smoke from a small fire can fill an entire room within seconds. It can also travel significant distances, moving into parts of the building far from the fire’s origin, posing a threat to occupants who may think they are in a safe location.

Smoke is composed of two main parts: the combustion products (solid and liquid particulates and gases) from the fire and the surrounding air that gets sucked into the hot smoke cloud. This air entrainment significantly increases the volume of the smoke, allowing it to rapidly fill spaces and spread throughout the building.

The technical definition of smoke is, “the airborne solid and liquid particulates and gases evolved when a material undergoes pyrolysis or combustion, together with the quantity of air that is entrained or otherwise mixed into the mass,” according to the ASHRAE Handbook of Smoke Control Engineering.

This rapid spread is why smoke control measures, such as pressurization and compartmentalization, are crucial to minimizing harm to occupants and slowing the movement of dangerous gases.

To learn more, check out my previous post below about the factors that influence smoke movement in buildings.

Key Factors Affecting Smoke Spread in Building Fires

Citations

1. Klote, J. H., Milke, J. A., Turnbull, P. G., Kashef, A., & Ferreira, M. J. (2012). Handbook of Smoke Control Engineering. ASHRAE.
2. Greiner, T. (2017, July 27). Carbon monoxide poisoning: Health effects (AEN-166). Department of Agricultural and Biosystems Engineering. Retrieved April 29, 2023, from https://www.abe.iastate.edu/extension-and-outreach/carbon-monoxide-poisoning-health-effects-aen-166/