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3 CHAPTER ONE INTRODUCTION This report provides the synthesis of results from ACRP Proj- sive, but also more effective than urea at lower temperatures ect S10-03. This introductory chapter, describing the purpose (-20F, 10F, and 5F, respectively) (Pro-Act Fact Sheet . . . and background of the report, provides the context for the 1998). In Canada, the general consensus was that the increased remaining chapters. effectiveness and simultaneous reduction in environmental problems justifies the increased cost of using new PDPs (Com- fort 2000). PURPOSE OF SYNTHESIS Airports and airlines deal with multiple objectives and are This synthesis reports on how airports chemically treat their challenged with multiple constraints when it comes to airfield airfield pavements to mitigate snow and ice, and the chemi- pavement deicing and anti-icing. First, aircraft safety (and cals used; reviews damage to aircraft components and air- mobility) is of the highest priority, which at times demands field infrastructure in association with the use of traditional large quantities of PDPs to be used for snow and ice control or modern pavement deicing products (PDPs) (for simplic- on airfield pavements. Because passenger and flight crew ity, this document uses the terms "deicer" and "pavement safety is of paramount importance, the aviation regulators deicing products" for all chemical products used for deicing and airframe and aircraft component manufacturers strive to and anti-icing operations); and identifies critical knowledge ensure the highest standards possible. For instance, critical gaps on these subjects. Field reports of the aviation industry control systems for aircraft are designed with an "extremely increasingly suggest that the use of PDPs, including alkali remote" probability of failing, which is one-in-one-billion acetate and alkali formate products (such as sodium- and (10-9) flights (National Academy of Engineering 1980). Air- potassium-acetate-, and formate-based products), on aprons, craft safety is also ensured by mandating regular regimes of runways, and taxiways may result in damage to various air- inspection, maintenance, and replacement of aircraft brakes craft and airfield infrastructure under certain conditions. and components to manage the highly improbable but poten- tially catastrophic risks. BACKGROUND Second, environmental regulatory compliance is an impor- Airfield pavement deicing and anti-icing are essential activi- tant objective as a result of requirements of the Clear Water ties in maintaining the aviation industry's safe winter opera- Act and National Pollution Discharge Elimination System tions. The general preference for aviation's winter maintenance permits for stormwater discharges. Officials at more than practices is anti-icing with approved chemicals to prevent the half of the airports that responded to a 2000 U.S. General bonding of ice and pavement--a more proactive approach Accounting Office survey indicated that it was getting much than deicing or sanding. For anti-icing, liquid chemicals are more difficult to balance environmental concerns with their preferred for their better dispersion and adherence, because airport's operations (General Accounting Office 2000). The solid chemicals can be easily scattered by wind, aircraft, and EPA is in the process of developing effluent limitation guide- ground support vehicles. For deicing, chemicals are applied to lines for airport deicing and anti-icing operations that may melt ice and disrupt any bond to the pavement, whereas sand pose additional challenges for airports and airlines in achiev- can increase the frictional characteristics of the surface ("Air- ing environmental compliance. The use of liquid glycol-based port Winter Safety and Operations" n.d.). Mechanical methods and solid urea deicers has received particular scrutiny owing can reduce the amount of deicing chemicals applied; however, to the high biochemical oxygen demand [BOD, often mea- care must be taken to avoid polishing ice and creating a haz- sured as 5-day BOD (BOD5 in mg/L)] exerted on receiving ard that is more difficult to treat (Pro-Act Fact Sheet . . . 1998). bodies of water. Depleted oxygen levels can threaten aquatic life, whereas the ammonia by-product of urea is toxic to The traditional airfield PDPs consisting of urea or glycols aquatic organisms (Pro-Act Fact Sheet . . . 1998). Although have become less popular owing to their adverse environmen- glycol-based deicers are increasingly less commonly used for tal impacts. New PDPs have emerged as alternatives that often pavement deicing, urea was still used by more than one-third contain potassium acetate (KAc), sodium acetate (NaAc), of the 50 busiest airports in 2000 (General Accounting sodium formate (NaF), or potassium formate (KF) as the freez- Office 2000) and more than one-third of the airports that ing point depressant. KAc, NaAc, and NaF are more expen- reported using chemical deicers by a more comprehensive