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Liquid Chemicals in Snow and Ice Control

Liquid Chemicals in Snow and Ice Control. Chemicals: How do they work?. Depress the freezing point of water, turning ice or snow into liquid or slush Solid salts dissolve to form brine solution. Chemical Terms. Concentration % by weight of chemical in solution Eutectic Temperature

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Liquid Chemicals in Snow and Ice Control

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  1. Liquid Chemicals in Snow and Ice Control

  2. Chemicals: How do they work? • Depress the freezing point of water, turning ice or snow into liquid or slush • Solid salts dissolve to form brine solution

  3. Chemical Terms • Concentration • % by weight of chemical in solution • Eutectic Temperature • Lowest Temp solution will melt ice • Endothermic • Requires heat when going into solution • Exothermic • Gives off heat when going into solution • Hygroscopic • Draws water from the air

  4. Liquid Chemical Uses • Anti-icing • FHWA Manual • Pre-treatment Plan • Pre-wetting solids • Lower temperatures • Less bounce and scatter

  5. Anti-icing • Creating a chemical layer ahead of the event to: • Prevent freeze bond • Prevent frost or black ice formation • Increase needed response time • Anti-icing chemicals • Liquids • Pre-wetted solids

  6. Resource for All Snow & Ice Winter Maintenance Need • FHWA’s Manual of Practice for an Effective Anti-Icing Program http://www.fhwa.dot.gov/reports/mopeap/eapcov.htm

  7. Anti-icing Rules of Thumb • Less is Best • Applied in controlled amounts to leave surface merely damp • Does not result in the flow of liquid across the pavement • Monitor Pavement Temperatures • Quick re-freeze occurs at lower temperatures • Monitor Humidity • Higher humidity can cause slickness issues • Does not replace de-icing techniques

  8. Pre-wetting Solids • Improves effectiveness at lower temperatures • Reduces bounce and scatter • Application at auger (not spinner) is most effective • Rule of Thumb – It is always more efficient to pre-wet solids

  9. Typical Liquid Products • Natural Occurring Salts • Sodium Chloride – 23% solution • Calcium Chloride – 32% solution • Magnesium Chloride – 28% solution • Potassium Chloride • Other Chemicals • Urea • Calcium Magnesium Acetate • Agricultural Products – Both by-products and engineered products • Various Additives

  10. Phase Diagrams

  11. Evaluating Snow & Ice Control Chemicals • Product Performance • Use Criteria • Infrastructure Impacts • Environmental Impacts • Availability • Cost

  12. Evaluating Snow & Ice Control Chemicals • Performance (deicing mechanics) • Effective temperature range • Speed • Quantity needed • Duration of melting action

  13. Evaluating Snow & Ice Control Chemicals • Use Criteria • Equipment requirements • Storage & handling needs • Application versatility • Safety & hygiene considerations

  14. Evaluating Snow & Ice Control Chemicals • Infrastructure Impacts • Structures (bridges, buildings) • Roadway pavement & structure • Vehicles & equipment

  15. Evaluating Snow & Ice Control Chemicals • Environmental Impacts • Soil • Animals • Vegetation • Water • Air • Human Health

  16. $$ Evaluating Snow & Ice Control Chemicals • Availability • Cost • Availability • Alternatives • Performance • Use Criteria • Infrastructure Impact • Environmental Impact

  17. Other Natural Salts • Calcium Chloride • Natural State - Liquid • Magnesium Chloride • Natural State - Liquid • Potassium Chloride • Natural State - Solid Common Use: Prewetting Anti-icing

  18. Calcium Chloride Exothermic: gives off heat Hygroscopic: attracts moisture Eutectic Temp: -60oF 30-33% concentration in solution Magnesium Chloride Exothermic: gives off heat Hygroscopic: attracts moisture Eutectic Temp: -28oF 22-26% concentration in solution Other Natural Salts

  19. CMA(Calcium Magnesium Acetate) • FHWA originally identified CMA as a possible replacement for salt in 1980. • CMA manufactured by reacting dolomitic lime with acetic acid.

  20. CMA Use • Bridge Structures • Parking Garages • Environmentally Sensitive Areas

  21. Corrosion • More corrosive • Calcium Chloride • Sodium Chloride • Magnesium Chloride • CMA • Urea • Less Corrosive

  22. Chemicals • Specifications • Material Safety Data Sheet (MSDS) • Sample and test (certification) • Talk to other users: effectiveness, concerns, problems • Storage Issues – some chemicals require circulation

  23. Material Handling • Safe Chemical Handling • Labels • MSDS (Material Safety Data Sheet) • Personal Protective Equipment “Common Sense” & the “Right Attitude!”

  24. MSDSMaterial Safety Data Sheets • Manufacturer’s Data • Product ID • Major Components Hazardous Ingredients • Physical Data • Fire & Explosion Data • Reactivity Data • Health Hazard Info • Emergency & First Aid Procedures • Personal Protection Equipment • Spill, Leak & Disposal Procedures

  25. Chemical Handling • Toxicity vs. Hazard • Hazard = toxicity + exposure • Toxicity: LD50 & LC50 “Just how toxic are snow and ice control chemicals to human health?”

  26. Toxicity Classification

  27. Toxicity Comparison *LD50(rat, mg/KG body wt.)highest toxicity first

  28. Snow & Ice ChemicalsCommon Potential Problems • Eye Irritant • Skin Irritant • Breathing Irritant - Dust or Mist Inhalation “Good Personal Hygiene & Personal Protective Equipment”

  29. Chemical Handling • Gloves • Shoes & Boots • Eye Protection • Dust Mask • Attitude

  30. Choosing a New Chemical • A big opportunity (as you shift to liquids) • What do you need the chemical to do? • What constraints do you have on how the chemical will perform? • Approach is based on the “Guide for Selecting Anti-Icing Chemicals” • Copy included on reference disk

  31. Purpose of the guide • Differentiate between different chemicals • on the basis of performance • acknowledge that different agencies have different needs • allow factors to be weighted

  32. Freezing point depression Consistency Viscosity Specific gravity Environmental Impact Heavy metals BOD/COD Toxicity Stability Corrosion Handling Documentation Unspecified content Completeness Categories Used

  33. Most Important Ones • Depends on your needs • Is corrosion a big issue for you? • What about the environment? • Definitely freezing point depression • Consistency • Complete documentation

  34. Why Freezing Point Depression? • Tells whether it’s suitable for your climate • Tells when you should stop using it because it’s too cold • Tells how much you’ll need to fight a typical storm

  35. How Freezing Point Depression? • Based on the eutectic curve • BUT, not just the eutectic point • It’s more an indicator of melting action • Need to know two temperatures • At half the concentration of the EP • At quarter of that concentration

  36. How does NaCl do? • The half point is about 15 F • Typically represents lower end of the useful range of salt use • The quarter point is 26 F • Illustrates impact of dilution

  37. Chemical Comparison

  38. Chemical ComparisonEutectic vs Effective Temp

  39. What about Consistency? • The addition of organic chemicals and by-products makes some new liquid products much more variable than traditional chemicals • You MUST know that the product you use this week performs the same as what you used last week

  40. How do we Measure Consistency? • Have to use index tests • Viscosity and specific gravity are easy to do and will quickly tell you if something isn’t right • The only long term answer is good quality program with suppliers

  41. Why Documentation? • You can’t compare products if you don’t have enough information • Any worthwhile product will come with documentation, test results and so forth • Provide a critical input for your choice

  42. How Documentation? • Two factors • How much of the product is termed “other” in the chemical analysis? • Do the suppliers give you all the info you need?

  43. Another factor for Consistency and Documentation • Legal issues • You HAVE to know what you’ve put on the road • If you don’t, you are very vulnerable during the deposition/trial process

  44. So how do we rate different products? • Set levels within each category • Weight the categories according to which matter to you • Then grade the chemicals (multiply their category level by their weight to get a grade point score) • See the guide for more details

  45. Pacific Northwest Snowfighters • http://www.wsdot.wa.gov/partners/pns/ • Evaluate and establish specifications for materials used in winter maintenance • Approved product list

  46. Salt Institute • Salt Institute http://www.saltinstitute.org/ • Salt Institutes “Winter Maintenance Material: What are you Using?” • Salt Institute’s “Are You Using the Right Amount of Ice Control Chemical?” (based upon findings of NCHRP 6-13) • Copies included on reference disk

  47. SICOP Website • Snow and Ice Pooled Fund Cooperative Program, SICOP http://www.sicop.net • Snow and Ice List Serve http://www.sicop.net/snow_and_ice_list-serve.htm

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