Coping With Toxic Smoke and Soot From Wildlands Fires

Dec 20, 2018

Since the passage of the Clean Air Act in 1970, US energy consumption has increased by 47%, and the population has increased by 50%, but air pollution emissions of the six most common pollutants -- carbon monoxide, volatile organic compounds, particulate matter, sulfur dioxide and nitrogen oxides -- have decreased 72%, and lead emissions nation-wide have been reduced by 99%. 

The air in major US cities in much better and it’s definitely influencing public health. For example: the rate of chronic respiratory disease in Detroit is 1/3 of what it was in the l970’s, and in Los Angeles there has been a steep decline in air pollution since the mid-1990s. 

However, another source of air pollutants is increasing – wildlands fires. On average, more than 100,000 wildlands or forest fires clear 4 million to 5 million acres of land in the U.S. every year.  From January 1 to November 30, 2018, there were a total of 52,303 significant wildfires, compared to 56,186 in the same period in 2017. About 8.5 million acres were burned in the 2018 period, compared with 9.2 million in 2017. 

This past year there were at least 110 large wildlands fires on almost two million acres in California, Idaho, and Oregon alone. Add to that in August of 2018, 559 fires of all sizes were burning in British Columbia, contributing to air pollution caused by US wildlands fires. 

The smoke released by any type of fire is a mixture of particles and chemicals produced by incomplete burning of carbon-containing materials. Smoke from these fires reached the East Coast as well as southern California and all through the Rockies. The National Preparedness Level was at the highest level of 5. 

Wildlands fires have been around as long as there have been lightning and trees. Fire plays a vital role in the maintenance of the health of many ecosystems in part by stimulating the establishment and growth of particular trees and other plants. Many wildland species, such as the lodgepole pine in the West and jack pine in the Midwest, require fire to regenerate. However, wildfire can also be the cause of significant economic and ecological losses and can pose threats to people, property, and communities. 

Wildlands fires aren’t just sending up clouds of smoke that effects people living in the woods. 32% of U.S. housing units and 1/10th of all land with housing are situated in the wildland-urban interface. 

Damage from fires can be destructive to homes, buildings and autos, as well as livestock, pets and people. People die from wildlands fire based on exposure. People can be burned to death. They can also be asphyxiated, especially if they are caught indoors or in a car that couldn’t make it out of the fire zone.   The 2018 Camp fire in northern California killed 86 people. Sixty percent of the victims were in their 70s, 80s or 90s, and 60% were found inside homes. Another 20% were found just outside of homes. Eight were found in cars headed for safety. This is the most deaths ever from a wildfire in California.

Regardless of what you think about global warming, wildlands fires are here to stay, especially as the number of people living in wildlands or near them is growing. According to the US Forest Service, approximately 60% of all houses built in the United States during 1990s were constructed within the wildland-urban interface.   Just how should you deal with it if you encounter the smoke from a wildlands fire?

To get the facts, I contacted with Dr. Richard Wade. Dick grew up in Maine and he has been Director of Environmental Health for the City of Seattle and King County and the State of Minnesota; Deputy Chief of the California Occupational Safety and Health (Cal/OSHA); taught at several major universities in the US and England, and from 1982-1990 he was the chief toxicologist for the San Francisco Fire Department. Dr. Wade holds top secret national security clearance and presently is a principal scientist at MicroDecon LLC.  

The following is a synopsis of what Dick told me about wildland fires.

It’s estimated that each ton of biomass burned produces 4% mass of particulate matter. Each year wildland fires produce an estimated average of 25 metric tons of particulate matter. When you look at air pollution nation-wide for the US, this is a large fraction of the particulate matter produced in the U.S each year from all sources. 

Ash generated by wildfires can travel for hundreds of miles. It reaches thousands of feet into the atmosphere and travels with ambient wind patterns to spread over many thousands of square miles. The nature of the wildfire ash (smoke) and its distribution depend on the temperature reached in the wildfire, the types of fuels being combusted, ambient winds and vertical thermal vectors that push the wildfire ash upwards.

The larger particles fall out in closer proximity to the fire zone and the small particles are carried further away from the fire zone. All sizes of particles can be found for hundreds of miles from the immediate fire zoneThese particles include all the solid thermally decomposed chemical components of the combusted vegetation, including minerals and carbon molecules. In some cases, the particles also include combusted end products from structures burned by the fire.  

Wood and other biomaterial materials combusted during wildfires produce smoke that’s mostly composed of ash and char, traces of soot, as well as both volatile and semi volatile organic gases. The wildfire “smoke” is composed mostly of small particulate matter. Some of these particles definitely can irritate the eyes, nose and throat. 

Any of the gaseous emissions such as carbon monoxide, carbon dioxide and more complex organic and semi volatile organics are either consumed by the fire or diluted in the atmosphere such that they never reach impacted properties outside the fire zone. Gases created in a fire zone tend to be burned very quickly by the intense heat of the fire. Noxious gases tend to quickly dissipate or settle to the ground very quickly. Studies of firefighters on the front line in firefights show that they do not experience any significant elevated levels of C02 exposure nor exposure to any toxic gases wildfire particulates generated by the wildfire that exceed any federal health standard. This is because the firefighters cannot work in the direct flame and combustions zone but must work in close proximity.

About 60% of the soot is carbon and trace amounts of minerals.  Based on a review of hundreds of industrial hygiene studies, very small amounts of soot are in wildfire ash residues found in wildfires. Health impacts from inhalation can be especially harmful to adults with preexisting health conditions such as emphysema, asthma, chronic respiratory conditions, heart disease, and to children in general. For this reason, persons are advised to avoid prolonged exposure to these airborne particles.  

In general, the closer to the proximity of the wildfire zone, the heavier the particles. Wildfire smoke (ash and char) is very different in its chemical composition than smoke from structural fires. After the suspended particles of wildfire ash have settled onto surfaces and are no longer airborne, they are of very low health risk since they can no longer get into the lungs or cause eye and throat irritation. Wildfire ash is a danger to human health only when it’s airborne. When particles fall into waterways, however, they can have toxic results for fish and wildlife.

Ash from wildfires and residential structures burned in wildfires should be handled as regular nonhazardous waste and disposed of in solid waste landfills.

Wildfire ash deposition drops off rapidly as one moves out of the immediate fire zone (from 20% in the fire zone to 2% at one quarter mile from the fire zone). Wildfire ash is water soluble and can be readily vacuumed with a HEPA vacuum or normal washing.

The pH of wildfire ash once deposited outside the fire zone is more neutral, and thus has a reduced risk of producing damage to building materials or contents. There is no supporting evidence that deposited wildfire ash concentrations up to 50% causes any changes in color or damage to building material/content surfaces. 

Post fire odor in properties is transient and caused by the residual of airborne particles. 

Common household fabrics that have been exposed to concentrations of up to 100% forest fire ash, when cleaned using common laundering, vacuuming and carpet steam cleaning techniques do not experience short-term fabric damage. 

Remedial actions on most wildfire property can be done by normal cleaning such as vacuuming and washing. Such sites do not require the services of fire restoration contractors or other specialized remediation contractors.

What Can You Do About The Fires?

There will always be wildlands fires caused by lightning. However a s many as 90% of wildland fires in the United States are caused by people.   Some are accidental. Others are purposeful. A study published in 2017 in the journal PNAS found that, at the national level, debris burning is responsible for 29% of wildfires and arson causes 21% of fires. Campfires accounted for just 5%. The CAMP fire apparently was started by a faulty electric power line. 

Dry years make things worse, but a significant part of the problem is too much vegetation due to lack of normal natural fires. There are more trees now than there were 100 years ago, and more are being planted each year than are harvested. In many northern California forests, the forests are so overgrown there are 10 times as many trees as there would be in a healthy, natural forest. All of that overgrowth and undergrowth, dried out from hotter and longer summers and a history of suppressing wildfires, is a big reason why we're now seeing deadly wildfires. Also, excessive plant growth can cause a decline in deer, such as when oak trees are crowded out by faster growing plants.

The Forest Service needs more support to clean out excess vegetation. They welcome organized groups to help remove excess vegetation. Help USFS and Smokey the Bear will definitely thank you. 

 — James A. Swan, Ph.D.