Evidence based guidance for public health decision makers during wildfire smoke events

Introduction

Wildfires are a widespread global occurrence. Wildfire activity is predicted to increase with global climate change due to longer fire season and larger geographic area burned. This trend is predicted to start in northern regions and cover the globe by the end of this century. Recent extreme fire seasons in Australia (2009), Russia (2010) and Texas (2011) and temperature-associated increases in area burned in North America provide some evidence that this is already occurring. Such severe fires are likely to exceed potential capacity of fire suppression and become uncontrolled. This means that we can expect more fires burning longer and generating more smoke.

Studies from several continents have demonstrated that particulate matter from wildfires is associated with increased respiratory medication use, physician visits, and admissions to hospitals. The evidence for cardiovascular events is surprisingly weak, although toxicologic evidence suggests that such an effect should occur. Differential susceptibilities of population subgroups such as children, elderly and those with chronic diseases, is still emerging. The study of health impacts from wildfires remains an active area of research.

General guidance for public health response to wildfire smoke events has been published by the World Health Organisation and Lipsett et al. Several Canadian and US health agencies have produced their own guidelines based on these two documents. However, recent studies provide more specific understanding of who is susceptible, how to best assess smoke exposure and health effects in real time, and which interventions are effective. Meanwhile, an international cadre of experts in wildfire smoke behaviour, exposures, and health effects is developing.

Objective:

This guidance aims to improve implementation of health protection measures during wildfire smoke events by providing evidence based recommendations for public health and emergency management professionals. It provides specific information about: who is susceptible, when to act, and which interventions best protect populations from wildfire smoke.

Method:

Guidelines were developed using an approach modified from the National Institute for Health and Care Excellence methods to formulate public health guidance and guided by the Appraisal of Guidelines for Research and Evaluation II instrument. A scientific advisory committee was formed in December 2012, comprised of researchers and public health officers with expertise on public health response, wildfire epidemiology, and wildfire behaviour. Topic areas for evidence reviews were formulated based on a structured review of current wildfire smoke guidelines and expert opinion of the SAC.

Nine systematic evidence reviews were completed in April 2014 on the following topics: wildfire smoke, health effects of wildfire smoke, smoke surveillance, health surveillance, reducing time outdoors, using masks, clean air shelters, air filtration in institutions, and evacuation. A cross-disciplinary meeting was held in April 2014 where agreement was reached on key approaches. Wildfire smoke response guidance has been drafted and is currently undergoing internal scientific review using a modified Delphi process to resolve any disagreements.

Results:

Preliminary guidance based on the evidence reviews and expert consensus is provided here. This guidance is currently under review by our scientific advisory board.

We found conclusive evidence that wildfire smoke is causally related to exacerbations of asthma and chronic obstructive pulmonary disease (COPD) and growing evidence of its effect on incident respiratory infections and pneumonia. Other morbidities with weak but plausible associations include: cardiovascular events, anxiety, eye irritation and respiratory symptoms. There is strong evidence of susceptibility for people with asthma and COPD and there is limited evidence for fetuses, children, the elderly, those with lower socioeconomic status and the elderly.

Surveillance of wildfire smoke events includes both smoke and health outcome surveillance with state-of-the-art systems incorporating both. Predictive models are used to forecast smoke, but such models have not been developed for health outcomes. More work is needed to evaluate surveillance during wildfire smoke events and to develop guidance for how surveillance can best inform public health response.

Public service announcements influence some parts of the population to take health protective measures but certain populations have better uptake: those with chronic respiratory disease, of higher SES, young and middle aged adults (versus elderly) and people who receive advice in their native language.

The most effective masks for reducing wildfire smoke exposures are N95 respirators which can provide a 10-fold reduction in fine particulate matter. However, effectiveness requires good fit and proper use. Therefore use is best limited to adults who must be exposed to wildfire smoke due to occupational or other requirements and where proper fit and use can be achieved.

The evidence supports the use of clean air shelters (CAS) to protect people from wildfire smoke. CAS can be set up in homes or community settings. Filtration with either portable high efficiency particulate air or electrostatic precipitators has been shown to effectively reduce indoor smoke concentrations in household settings. Few research studies have investigated health benefits, but those conducted suggest improved markers of cardiac impairment in adults and reduced asthma symptoms in children in home CAS. In-duct filtration with standard heating ventilation and air conditioning (HVAC) systems provides limited reduction in smoke particulate PM_3-10 (e.g., typical induct filter provides 20-70% reduction in PM_3-10). Filtration of particles in the finer range, which dominates wildfire smoke, is achieved with more efficient filters (e.g., augmented filtration found in some hospitals provide 75 to >95% reduction in PM_0.3-1). An HVAC engineer must be consulted to ensure that HVAC functions are retained with increased filtration. We found no peer-reviewed evaluation of augmented filtration during wildfire smoke events.

We found no well-designed peer-reviewed studies that evaluate the effectiveness of evacuation during wildfire smoke events. Expert consensus was that evacuation should be recommended when: severe smoke hazard lasts longer than a week, toxic wildfire smoke occurs due to contamination of fuels source with hazardous substances, when in-situ CAS are not capable of providing adequate exposure reduction, the exposed population is particularly susceptible to smoke or severe health effects occur among the exposed.

Conclusions:

This is the first guidance for population health protection during acute wildfire smoke events that has been produced using standard methods for developing evidence based public health guidance.