In recent years, extensive wildfires and smoke exposure have impacted horse operations around North America. Evacuation and preventive protocols are often challenging and put a great deal of strain on livestock and their human caretakers.

Equally as concerning is the risk of on-site fires. With long periods of drought recurring across North America year after year, building fires are an increasing threat to the health and safety of many equine facilities.

Fires pose considerable danger to horses, even from a significant distance. In particular, horses can suffer from varying degrees of poisoning and injury associated with smoke inhalation.

Symptoms of smoke inhalation injury in horses vary depending on the severity of exposure, the specific chemical composition of the smoke, and the presence of pre-existing respiratory conditions. The prognosis varies from good to extremely poor depending on the duration of exposure, underlying conditions, and severity of symptoms.

Prepare yourself for emergencies by learning why smoke is a toxic hazard for your equines and what steps you can take to protect your herd.

Equine Air Quality Index Tool

Fire Hazards for Horses

Every year, horses around the world perish or are injured due to barn fires. Uncontrolled fires also spread through vegetation, often exacerbated by dry conditions, high temperatures, and strong winds.

When material combusts, it undergoes a rapid oxidative reaction with oxygen from the air that releases light, heat, and the by-product smoke. [1]

Smoke is a complex and evolving mixture of hot air, carbon gases, solid particulates, fumes, and vapors emitted as substances combust.

The chemical composition of smoke is highly variable depending on the properties of the burning material and the fire environment. Fires with ample oxygen availability burn hotter and produce less smoke than those in oxygen-poor spaces. [1]

Components of Smoke

Most of the properties of smoke are hazardous to horses in some way. Common components of smoke include: [1][5][6][7]

  • Carbon dioxide (CO2): a common by-product of wildfires and is not highly toxic. However, if CO2 displaces most or all of the oxygen in an enclosed space, it can lead to suffocation.
  • Carbon monoxide (CO): a toxic gas that can result in severe poisoning if inhaled. Lower-temperature fires produce higher concentrations of CO.
  • Hydrogen cyanide (NCH): a highly poisonous chemical compound formed when materials high in nitrogen burn.
  • Particulate matter (PM): a mixture of solid and liquid air droplets, which vary in diameter from 10 to less than 2.5 micrometers; Particulate material in fire smoke is the result of incomplete combustion; when inhaled, PM can settle in the lungs, interfering with their overall health and function.

In addition, the following compounds commonly found in smoke are all severely irritating to the respiratory tract: [3][4]

  • Ammonia
  • Hydrocarbons
  • Nitrogen oxides
  • Hydrogen sulfide

Types of Fires

Fires can be divided into two main categories: structural fires and wildfires, depending on the fuel source. Both categories of fires can be ignited naturally or by humans, and both pose a threat to horses. Further, wildfires can spark structural fires and vice-versa.

Structural Fires

Structural fires are fires that involve the combustion of building components. Smoke from these fires is rich in carbon monoxide, a colorless, odorless gas that displaces oxygen from the horse’s red blood cells, leading to suffocation. [4][8]

Burning plastics and other nitrogen-containing materials (e.g., wool, nylon, and silk) commonly found in horse apparel, tack, and other equipment release hydrogen cyanide, which is highly toxic. [4][8]

Thermal breakdown of synthetic materials like those often stored in barns where horses are kept can produce irritating fumes like ammonia and sulfur dioxide, causing severe respiratory tract damage. [4][8]

Barn Fires

While all structural fires can cause death and severe injury to horses and humans alike, barn fires are of particular concern in the equine community. These fires constitute a severe threat to farm animals, with hundreds of thousands of deaths reported each year. Between 2013 and 2023, over six million deaths due to barn fires were reported. [2][9]

In the upper Midwest and northeastern states, most barn fires occur in winter, representing 37% of annual fires. The leading cause of barn fires in the United States is malfunctioning electrical heating devices such as heat lamps and space heaters. [9]

Other common causes include: [9]

  • Electrical malfunctions (other than heating equipment): 25%
  • Machinery: 17%
  • Other causes (weather-related fires, wildfires, vehicle crashes, spilled gas, fireworks): 14%
  • Arson: 4%

Wildfires

Wildfires are unplanned fires that burn vegetation, including trees, grasses, and brush. While destructive, wildfires are a natural occurrence in many ecosystems. They play a vital role by consuming dead vegetation, clearing debris, and stimulating new plant growth. [10][11]

Wildfire smoke is a complex mixture of chemical compounds, including carbon dioxide, water vapor, nitrogen oxides, and particulate matter. Wildfire smoke is particularly high in fine particulate matter, which is the primary health risk to horses and humans. [4][10]

Smaller than 2.5 micrometers in diameter, these tiny particles can bypass the upper respiratory tract and reach the lower airways (alveoli) in both animals and humans. [4][10] A sufficiently high exposure to fine particulate matter, whether by a large single dose or chronic low dose, can impair overall health and function in the lungs.

Smoke Inhalation Injury

Horses exposed to smoke can suffer from a wide range of injuries affecting multiple organ systems, from thermal burns to secondary pulmonary infections. A general term for adverse health effects related to smoke exposure is smoke inhalation injury.  [12][13]

Symptoms of smoke inhalation injury in horses vary and are correlated to several factors, including:

  • Chemical composition of smoke