Field Notes
U.S. Fish & Wildlife Service
Field Notes Entry   
Service Agrees that Aerial Applications of Fire Retardant on National Forest System Lands are Not Likely to Adversely Affect Indiana Bats
Midwest Region, September 30, 2011
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U.S. Fish and Wildlife Service field offices in 16 states reviewed the U.S. Forest Service’s June 2011 Biological Assessment which describes the Forest Service’s proposed continued use of aerial applications of fire retardant on National Forest System Lands as part of interagency consultation under section 7 of the Endangered Species Act. The Service collectively evaluated the BA and ultimately concurred with the Forest Service’s determination that the proposed activity may affect, but is not likely to adversely affect, federally endangered Indiana bats (Myotis sodalis). On September 9, 2011, the Bloomington, Indiana, Field Office, the Service’s “recovery lead” for the Indiana bat, issued the Forest Service a concurrence letter covering aerial applications of fire retardant on all National Forest System Lands within the range of the Indiana bat.


The Forest Service primarily uses aerial applications of fire retardant to provide additional safety to firefighters during wildfire suppression actions. Firefighters are taught to request retardant drops if they are in a hazardous situation such as a last resort survival. Retardant has been used to provide firefighters time and support during wildfire entrapments. The vast majority of retardant is aerially applied in the western United States; it is rarely used in the Northeast and Midwest and is periodically used on some forests in the Southeast, depending on the severity of a particular fire season.

Retardant is typically applied to fuels in front of an advancing fire, not directly to the fire. It is comprised of ammonium sulphate or ammonium phosphate salts, thickeners, dyes and corrosion inhibitors  and slows the rate of fire spread by cooling and coating fuels, robbing the fire of oxygen, and slowing the rate of fuel combustion. The retardant slurry acts as a barrier in front of a fire and, as the fire burns into the areas coated with retardant, the salts are converted to sulphuric and phosphoric acids with the release of sulphur dioxide, ammonia and nitrogen oxides. This reaction suppresses the flaming combustion of fuels. Resulting impacts within the retardant application area render some vegetation completely burned and some vegetation and ground unburned but covered with retardant. Retardant formulations in use today are primarily inorganic fertilizers, the active compound being ammonia polyphosphates. Whenever practical, as determined by the fire incident command, the Forest Service will use water or less toxic fire retardants in areas occupied by or designated critical habitat for threatened, endangered and proposed species. In addition, the Forest Service will avoid using retardant within a 300-foot buffer of perennial and intermittent streams, lakes, ponds, identified springs and reservoirs.

Based on information within the BA, exposure analyses, and informal consultations among Service biologists and individual National Forests, Service biologists anticipate that relatively few wildland fires are likely to occur on Forest Service lands in the Eastern U.S. within the range of the Indiana bat during the species’ active season (i.e., summer months) that would necessitate the use of fire retardant.  Thus the bats would have an extremely low probability of being directly or indirectly exposed to aerial applications of fire retardant. Therefore, incidental take of Indiana bats from this activity is not reasonably certain to occur.

Contact Info: Andy King, 812-334-4261 x1216, Andrew_King@fws.gov
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