Comparison of Ethylene Glycol- and Propylene Glycol-Based Aircraft Deicing Fluids Agenda
• Executive Summary • Chemistry • Operational Properties (for the aircraft) o Freezing Point (efficiency) o Lowest Operational Use Temperature o Holdover Time and Allowance Times • Mammalian Toxicity o Operator Precautions • Environmental Toxicity o Aquatic Toxicity o Air Emissions / Vapor Pressure o Biodegradation Executive Summary
• Both ethylene glycol- (EG) and propylene glycol- (PG) based aircraft deicing fluids (ADFs) consist of the base glycol plus water and additives • Operationally, EG-based fluids perform better: • Less EG is required to produce the same freezing point than PG. • Lower viscosity means EG-based fluids provide better aerodynamic performance at colder temperatures. • As a result, EG-based fluids have superior Holdover Times (HOTs) compared to PG-based fluids, as presented by the SAE G-12 HOT Committee in May 2017. • Mammalian Toxicity • EG and PG both have low to moderate acute toxicity. • If ingested in a large, single oral dose, EG is more toxic to mammals than PG. • Oral dosing is an unlikely route of exposure during deicing. • History in Canada, where EG fluids have been used safely for many years, confirms operator procedures can appropriately manage this risk. Executive Summary
• Environmental Properties • EG-based fluids in concentrated form generally demonstrate better aquatic toxicity than PG-based fluids; however, both are non-toxic. • Mixtures of EG-based ADFs exhibit less air emissions than PG based fluids.1 • Both EG and PG are biodegradable in the environment and neither bio accumulates. • PG has higher Theoretical Oxygen Demand and requires a higher usage concentration than PG fluids. • The net effect is 30-45% higher Biochemical Oxygen Demand for airport operations using PG rather than EG on an equivalent freezing point basis. • Economic Comparison • EG fluids have historically had less volatile feedstocks than PG fluids, and that is expected to continue. • Supply of EG Fluids • The EG market in North America is large and diverse. There are 10 major producers of EG compared to 5 producers of PG. Total EG capacity is 4.1 million MT, compared to 0.8 million MT for PG • This EG supply can offer greater fluid reliability during peak weather events.
1 McCready, David, “Estimation of Glycol Air Emissions from Aircraft Deicing”. 91st Annual Meeting of Air & Waste Management Association, San Diego, California, 1998 EG and PG Fluid Chemistry EG/PG
Ethylene Glycol (EG) HO-CH2CH2-OH
Propylene Glycol (PG) HO-CH2CH -OH l CH3
EG and PG are the base chemicals to which ingredients are added to make deicing or anti-icing fluids.
Formulated Fluid EG or PG plus water plus additives
5 Operational Properties Freezing Point Performance
Freezing Point vs. Percent Glycol
7 Freezing Point Performance
The lower the molecular weight, the more effective it is:
Freezing Point vs. Percent Glycol EG (MW 62) is more efficient than PG (MW 76)
Less EG is required to produce the same freezing point than PG When using Dow fluids, one needs 5-11% less volume, with 10% as the average over all temperature ranges. 8 Viscosity Performance
• Solutions of ethylene glycol have lower viscosity than propylene glycol for the same freezing point.
50% EG at -20oC → ~22 mPa sec 52% PG at -20oC → ~85 mPa sec
• Consequently, Type I EG-based fluids provide better aerodynamic performance at colder temperatures.
9 Aerodynamic Acceptance Limits of UCAR™ EG- and PG-based Type I Fluids
Aircraft Type EG PG High Speed -45C -34C Low Speed -40C -25C
™Trademark of The Dow Chemical Company ("Dow") or an affiliated company of Dow Type II/IV Generic HOTs – Cold Temperature
*Transport Canada will include single HOT value in very light snow cells
Data from “Changes to HOT Guidelines for Winter 2017-18” as presented by SAE G-12 HOT Committee, Athens Greece – May 23, 2017 11 New Type II/IV Fluid-Specific HOTs – Cold Temperature
LOUT = -22.5 oC
LOUT = -22.5 oC
*Transport Canada will include single HOT value in very light snow cells Data from “Changes to HOT Guidelines for Winter 2017-18” as presented by SAE G-12 12 HOT Committee, Athens Greece – May 23, 2017 New Type II/IV Fluid-Specific HOTs – Cold Temperature
67% - 74% 50% - 67% 32% - 50% 78% - 83% 40% - 71% 30% - 40% 71% - 82% 50% - 71% 35% - 50%
33% - 35% 25% - 33% 15% - 25% 33% - 39% 23% - 33% 10% - 23% 33% - 39% 23% - 33% 15% - 23%
25% - 29% 18% -25% 10% - 18% 25% - 29% 15% - 25% 5% - 15% 25% - 29% 15% - 25% 10% - 15%
90% - 100% 70% - 90% 90% 100% 100% 100% 133% - 171% 130% - 170% 80% - 130%
44% - 48% 38% - 44% 90% 100% 100% 100% LOUT = -22.5 oC
31% - 33% 20% - 31% 90% 100% 100% 100% LOUT = -22.5 oC
Comparison to EG106 derived from “Changes to HOT Guidelines for Winter 2017-18” 13 as presented by SAE G-12 HOT Committee, Athens Greece – May 23, 2017 Ice Pellet and Small Hail Allowance Time
There are several performance advantages for EG- vs PG-based fluids when considering ice pellet and small hail allowance time:
Temperature EG PG
-5 ºC and Above 25 minutes 15 minutes
No allowance times 5 - 30 minutes for aircraft with exists when used on rotation speeds of 100 knots Below -10 ºC aircraft with rotation or greater (varies depending speeds less than 115 on conditions) knots
Data from page 45 in FAA Holdover Time Guidelines Winter 2016-2017 original issue Aug 5, 2016 14 Mammalian Toxicity Mammalian Toxicity
• EG and PG are chemicals of low to moderate acute toxicity. • EG is more toxic to mammals than PG when ingested. • Hazard is a large, single oral dose resulting in metabolic saturation. • Oral dosing is an unlikely route of exposure during deicing.
16 Mammalian Toxicity Summary
17 ADF Operator Recommendations
• Studies have shown that exposures during deicer application are well below occupational exposure limits; however, this may not apply to every set-up and situation. • For most conditions, respiratory protection should not be necessary. • If employees want added protection in circumstances that do not exceed applicable exposure limits and discomfort is not experienced, then an air purifying respirator such as a P-series (P95) filtering face piece/dust mask is recommended. • If employees are experiencing discomfort or applicable exposure limits are exceeded, then the recommended respiratory protection for applications is an air purifying respirator with organic vapor/P95 pre-filter cartridges.
Note: The P-series filters are recommended by the respirator manufacturers for use with ethylene glycol (aerosol). According to 3M, P-series filters have been recommended for ethylene glycol aerosol pending more research as to how EG affects the filter fibers.
18 Environmental Properties U.S. Transportation Information
UCAR™ PG ADF Concentrate UCAR™ ADF Concentrate (EG)
™Trademark of The Dow Chemical Company ("Dow") or an affiliated company of Dow Aquatic Toxicity: Pure Glycols
Higher numbers are better 60,000 EG 50,000 PG 40,000
Fathead Minnow mg/L 30,000 96 hr LC 50 20,000 Rainbow Trout
72 hr LC 50 10,000 Daphnia Magna 0 48 hr LC 50 Fathead Rainbow Daphnia Minnow Trout Magna U.S. Fish and Wildlife Service Classification System for Acute Exposures defines "relatively non-toxic" as anything above 1000 mg/L. 21 Aquatic Toxicity: UCAR™ Deicing Fluids in Concentrated Form (92% EG, 88% PG)
Higher numbers are better
40,000 EG 35,000 PG 30,000 25,000
Fathead Minnow mg/L 20,000 96 hr LC 50
15,000 Rainbow Trout 10,000 96 hr LC 50
5,000 Daphnia Magna 0 48 hr LC 50 Fathead Rainbow Daphnia Minnow Trout Magna U.S. Fish and Wildlife Service Classification System for Acute Exposures defines "relatively non-toxic" as anything above 1000 mg/L. 22 Canadian Environmental Protection Act (CEPA) Guidelines
• 100 mg/L EG • 100 mg/L PG
23 Air Emissions – PG vs. EG
Air Emissions Mixtures of EG based ADFs (lbs glycol per 10,000 gal applied) exhibit less air emissions than 9 PG based fluids. 8 7 6 5 lbs 4 3 2 1 0 EG 50/50 PG 55/45 Deicing Fluid Deicing Fluid
McCready, David, “Estimation of Glycol Air Emissions from Aircraft Deicing”. 91st Annual Meeting of Air & Waste Management Association, San Diego, California, 1998 Vapor Pressure Comparison
250 WATER - 100 VOL%
200 PG - 50 VOL% EG - 50 VOL%
150
100 Pressure (mmHg) Pressure
50
0 0 10 20 30 40 50 60 70 80 Temperature (oC) Biodegradation: Pure Glycols
% Degraded at 20 days, 20º C: • EG 97% • PG 87%
• Both glycols are biodegradable in the environment. • Both glycols do not bio accumulate.
26 Theoretical Oxygen Demand (ThOD)
Mg of Oxygen Required to Degrade 1 mg of glycol • Less is Better… • The lower the number, the less oxygen depleted from receiving 1.8 waters. 1.6 1.4 • 1.68 (PG) /1.29 (EG) = 1.30 1.2 (30% less ThOD for EG) 1 0.8 0.6 0.4 0.2 0 Ethlyene Glycol Propylene Glycol 27 Net Effect of EG versus PG on BOD Loading
• PG has higher Theoretical Oxygen Demand (ThOD 30%, slide 23) and requires a higher usage concentration (5-15% due to PG’s higher MW, slide 6).
• Net effect is 30-45% higher Biochemical Oxygen Demand (BOD) for airport operations using PG rather than EG on an equivalent freezing point basis.
28 Review • Chemistry • Operational Properties (for the aircraft) • Mammalian Toxicity • Environmental Toxicity Contact Us United States and Canada Call toll-free 1-800-447-4369 Call 1-989-832-1560
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Updated: August 2017 110-01305-01-1219
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