There were 1,270 large or significant wildfires reported in 2012 in the USA. Significant wildfires represented about 1.9 percent of total wildfires reported nationally in 2012. Significant fires are defined in the National Mobilization Guide as fires that are a minimum of 100 acres in timber fuel types, 300 acres in grass and brush fuel types, or are managed by a Type 1 or 2 Incident Management Team, WFMT, or NIMO.

A total of 4,244 structures were destroyed by wildfires in 2012, including 2,216 residences, 1,961 outbuildings, and 67 commercial structures. This is well above the annual average of 1,416 residences, 1,253 outbuildings, and 46 commercial structures destroyed by wildfires (data from 1999 to present).
Source: www.predictiveservices.nifc.gov

On July 1, 2013, 19 wildland firefighters from the Granite Mountain Hotshots, an elite 20-member crew based out of Prescott, Arizona, died fighting the Yarnell Hill Fire, a 2,000-acre blaze southwest of Prescott. This is the biggest wildland fire fighting tragedy since 1994 when 14 firefighters were killed on Colorado’s South Canyon Fire, and it recalls the Mann Gulch blaze that burned over 12 smokejumpers in 1949.
Source: www.outsideonline.com

It is believed that three fires ( the Windy Pass Fire, the West Fork Fire, and the Papoose Fire) that struck Colorado USA on July 23, 2013, were a direct result of lightning. The fires killed one person and destroyed 109,615 acres of land. 

Health Threat From Wildfire Smoke: Did you know that smoke from wildfires is a mixture of gases and fine particles from burning trees and other plant materials? Smoke, including those from forest fires, can hurt your eyes, irritate your respiratory system, and worsen chronic heart and lung diseases.

Air quality: Did you know that smoke from wild forest fires contains particulate matter, carbon monoxide, atmospheric mercury, ozone-forming chemicals, and volatile organic compounds? They also cover large distances and have significant impacts on visibility, air quality, and health.