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The Health Hazard of Huge Summer Fires and Smoke

Los-Angeles-wildfire-smoke-air-pollutionMassive smoke plumes invaded the Pacific Northwest in early August 2017, and more smoke from wildfires may be a problem into early autumn across parts of the U.S. and Canadian West. In this guest post, wildfire expert and author Stephen Pyne (Arizona State University) looks at the history of our relationship with wildfire smoke.

Landscape fire occurs where land, air, and plants meet. Most of the focus is on flames, and where air and flame interact, on how winds push a flaming front like a tattered sail. But look at any image of a serious fire, and the largest feature is its plume. Fires are three-dimensional phenomena, more like a thunderstorm than a flood. The zone of the fire can extend deeply into the atmosphere. The effects of the fire can project, through its smoke, far from its perimeter. And recently that far-ranging smoke has become of global interest for its effects on public health and climate change.

Big smokes aren’t new. America’s frontier of settlement left the sky murky with seasonal smokes, some vast and dense. Several times in the late 18th century New England’s sky went dark at noon as immense smoke palls passed overhead. Those Dark Days foreshadowed others that occasionally smothered innumerable basins that pooled smoke along with cold air, including the Great Lakes. Entire fire seasons passed under haze, occasionally thickened into a dry fog of particulates.

smoke-air-pollutionDuring the 1864 fires in the Northwest, the Oregonian ran an article that speculated that “much of the sickness which prevails among us at present is attributed to the heated state of the atmosphere and the immense volumes of smoke created by the vast fires.” A few years later it proclaimed: “We read about Egyptian darkness, but it is smoke, Josephine smoke – smoke in the morning, at noon and at night. Meet a neighbor, it is smoke; parting from one, it is smoke. Hogs running around are smoked through and through – live, running bacon… so you see we live in the days of smoke. It is smoke, smoke, smoke!”

Then it disappeared, or at least the worst of it did. Settlement no longer churned up forests and incinerated slash, agriculture shrank its burning of field and fallow. Where it continued, as in the Northwest, public health and environmental activism found common cause to shut down slash fires and burning to stimulate grass seed production in the valleys. Society converted from the open burning of wood and grass to the internal combustion of fossil fuels. Emissions belched out, sometimes to the detriment of local towns, but most of it was invisible compared to woodsmoke, whose range of particulates coincides with the wavelength of visible light. (There were exceptions such as the Los Angeles basin, where trapped emissions could lead to smog.) In general, the skies cleared, and generations grew up with the expectation that blue sky year round was the norm.

Summer-wildfire-smoke-dangerIn recent years concern over smoke has marched in lockstep with alarm over the return of large landscape fires. The most notorious outbreaks involve the euphemistically termed “haze” that descends over Southeast Asia from massive burning in Borneo and Sumatra, mostly from tropical peat (in recent years such fires are among the largest sources of carbon dioxide released globally). The pall has shut down airports (like Singapore’s) and forced millions to breathe foul air and don surgical face masks. That concern has merged with studies of indoor air pollution from cooking fires fueled by wood and dung; with regional smoke from agricultural burning, such as in the Punjab region of India; and with medical investigations into the health hazards to firefighters from prolonged smoke inhalation.

Smoke, everyone concludes, is bad for you–even second-hand smoke downwind from the source of fires. Thanks to satellite imagery, news media routinely track smoke plumes. Especially where smoke is likely to be trapped in valleys from long-lingering fires, authorities broadcast public health warnings. All that burning, moreover, contributes to greenhouse gases, which fold back into conditions to support more fire.

Atmosphere-wild-fire-smokeA strong case has emerged to issue public alerts about bad air from smoke and to bring it under regulation. Lungs don’t distinguish among small particulates from cooking fires, trash fires, pastoral burning, coal-fired power plants, and lightning-kindled wildfires; neither does the atmosphere. Smoke is a hazard to near-term public health through occasional smoke-ins and to the long-term health of civilization through global warming.

But there is a paradox: many places need more fire, not less. Fire has been on Earth since the first plants colonized continents (fossil charcoal exists back 420 million years). We cannot abolish fire and smoke except in intensely managed built environments like cities where we can choose non-combustible materials (or face consequences like the Grenfell Tower fire in London). Removing fire can be ecologically disruptive, and devising alternatives can be hazardous (think of how many non-flammable materials turn out to be carcinogenic). The same is true for smoke. More and more research is pointing to the ecological role of smoke–the right kind of smoke at the right time. Smoke stimulates flowering in a variety of plants (including pineapple); it fumigates forests, helping control some moths and insects; it blocks solar heating in valleys that keep stream waters cool for migrating fish. As with fire, the more we look for benign smoke effects, the more we find.

In truth, America’s wildland agencies have sought to restore “good fire” for the past 50 years, and many wildland fire managers are haunted by the specter of regulations that would prevent attempts to introduce prescribed fire and to manage wildfires. Regulatory agencies like EPA need to define wildland fire differently from industrial combustion; they need to grant it some room, not just geographic space, but decision space. Smoke there will be, but we have some control over how much and when. Wildfires can produce huge volumes of smoke that can overload an airshed; prescribed fires can burn the same amount of land in smaller patches with better-vented and more easily diluted plumes.

That fire officers must manage smoke has been clear for decades, and they have done so. Smoke forecasts are as much a staple of planning as are winds. Smoke is an object of research, a theme of policy, and an obsession of practitioners. But it is harder to confine smoke than flames; it propagates much higher and farther. As a new era of settlement reclaims rural lands for exurbs, the prospects for smoke from good (as well as bad) fires to interact in dangerous ways with society increase. (Smoke drifting across roads has become a major issue.)

Even natural fires left to burn in remote places are likely to creep and sweep across the countryside for months, leaving a quasi-toxic legacy of smoke. There is nothing like being smoked in for weeks to arouse the public and perhaps lead to a public health crisis. Today, just as it did long ago, smoke can have a reach well beyond fire’s grasp.


Stephen Pyne

Steve Pyne is a Regents Professor in the School of Life Sciences at Arizona State University. He is the author of more than 30 books, including “Fire in America: a Cultural History of Wildland and Rural Fire” and an update, “Between Two Fires: A Fire History of Contemporary America.” Pyne spent 15 years as a firefighter with the North Rim Longshots at Grand Canyon National Park.


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