Appendix H New Revision. Insert the title of your. Appendix H of WMH. Appendix H New Revision. Appendix H New Revision

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1 Appendix H New Revision Appendix H is being updated based on the NWSRG Practical Guide Appendix H contains the most essential information distilled from the NWSRG Practical Guide Insert the title of your Introduction presentation to here the new Appendix H of WMH Presented by Name Here Job Title - Date The NWSRG Practical Guide is based around the most recent research and review of published information: - undertaken on behalf of the NWSRG with member funds - Independent work undertaken by member organisations including - Highways Agency, Transport Scotland & individual local authorities - Publically available International research and practice - Expert information and peer review by NWSRG members and industry associates. Page 2 Appendix H New Revision Sections of Appendix H cover: General winter service plans and service resilience De-icing materials and technologies Salt storage and management Spreader calibration and monitoring Decision Making Spread rates for precautionary treatments Treatments for snow, ice and freezing rain Treatments for extreme cold Appendix H New Revision Delivering a better service Many service providers can achieve significant savings, increased resilience and improved service levels by following the recommendations and detail in Chapter 13 and Appendix H Changes to plans, equipment, technology, etc. should be based on a business case relating to the particular service and treated network However, some recommendations and practices may take a number of years to implement (where adopted) Page 3 Page 4 1

2 Information and guidance on De-icing Materials: Types of de-icing materials Types of salting technology Salt storage options Salt stockpile maintenance Effectiveness of salt De-icers are not effective until they have dissolved to form a brine solution The rate of dissolution and ice melting slows at lower temperatures The practical effective temperature for salt as a road de-icer, when spreading - At or above -7 C in normal UK winter humidity conditions - At or above -5 C in low humidity conditions - below 80% relative humidity Page 5 Page 6 Effectiveness of salt Ice may be melted below the effective temperature, but at a very low rate - Unlikely to be practical for precautionary or post treatments. Below the effective temperature the amount of salt needed increases - Both economically and environmentally undesirable In theory, a saturated solution can prevent freezing down to -21 C In practice a saturated solution will not be formed - The minimum practical freezing point is no lower than -15 C - And even this is only achievable when sufficient time is available for a solution to form Salt Use Salt distribution by the spreader depends on: - Size - Grading - Moisture content Spreaders should always be calibrated for the salt grade being used and the moisture content Grading and moisture content should be checked regularly - particularly when salt is obtained from a new source or supplier. All salt must comply with agreed quality standards. Page 7 Page 8 2

3 Moisture content for salt Optimum salt moisture content Salt should be stored to maintain its moisture content within the optimum range for the spreading technology used Salt moisture content should be: - Kept at a consistent level - Should not differ from that used for spreader calibration by more than 1.5% Where salt moisture content is outside the optimum range take remedial action Page 9 Page 10 Salt storage options Different storage options - Salt barn/dome - Fabric covered structure - Outside under cover - Outside unprotected Consider - Relative cost of construction - Maintenance requirements - Control of salt condition - Effect on spread rates - Environmental requirements Salt stockpile maintenance Consider: - Stock rotation - Method of working of the stockpile - Turning /agitation of stockpiles - To be avoided if possible - Monitoring of salt condition Maintain salt after delivery to ensure: - Condition is maintained throughout the season - The stockpile is in a safe condition Page 11 Page 12 3

4 Stock rotation Storage priorities Salt should be used in order of delivery Should not be externally stored unprotected for more than one winter season Should not be externally stored under cover for more than 3 years unless tests confirm good condition Old stocks in barns should remain in good condition for a number of seasons Reserve stockpiles should be part of a rotation plan Priority for storing under cover: Highest priority: High purity/low insoluble content salt e.g. Marine Salt Lowest priority: UK rock salt Page 13 Page 14 Monitoring salt condition Monitoring salt condition Regularly check salt condition from new deliveries and existing stockpiles Develop test regime in consultation with the salt supplier Samples can be sent to UKAS accredited laboratories Additional simple checks on moisture content Suggested frequencies of testing Actions to take when moisture content is outside of the optimum range Page 15 Page 16 4

5 Loading spreaders Do not load thatch or large aggregations ( lumps ) Avoid contamination of the salt with detritus Salt spreaders should be sheeted during spreading - Protect the salt from snow and rain - Prevent losses from the hopper during spreading Spreader Calibration Information and guidance on: Spreader calibration procedures How to assess and monitor spreader performance Page 17 Page 18 Why is calibration so important? Ranking Prewet Dry Treated A B C D E F G H I J K L Calibration procedure Pre-calibration checks - of the salt condition and the spreader condition Discharge tests - measuring the amount of salt discharged with the spreader stationary and/or at speed, and making any necessary adjustments Visual check of the salt distribution - with the spreader stationary and/or at speed and making any necessary adjustments Issuing a calibration certificate - following successful completion of the discharge tests and distribution check Page 19 Page 20 5

6 Calibration procedure Calibration procedure Salt spreaders require calibration and set-up for: - The specific salt type - Grading - Moisture content. Calibration should always involve: Direct measurement of the salt being discharged Where it is being spread to Page 21 Page 22 Discharge tests Distribution check At what rate is the spreader actually discharging? A trial spreading run. Static discharge test with the spreader stationary Visual check of the salt distribution - To check the salt is being accurately spread to the target area Static or trial spreading run Assessment of the uniformity of the salt distribution as Good/Fair/Poor Guidance is provided on how to assess the distribution Page 23 Page 24 6

7 Distribution check Page 25 Table H7 Assessment of Uniformity of Salt distribution from observed run Salt type Uniformity Observation of distribution to two lanes Treated and pre-wetted Dry Good Fair Poor Good Fair Poor Distribution appears uniform between the lanes Wastage assessed to be less than 5% Up to 50% more salt assessed to be in one lane than the other Wastage assessed to be less than 10% Up to 75% more salt assessed to be in one lane than the other Wastage assessed to be less than 15% Up to 20% more salt assessed to be in one lane than the other Wastage assessed to be less than 10% Up to 75% more salt assessed to be in one lane than the other Wastage assessed to be less than 15% Up to 90% more salt assessed to be in one lane than the other Wastage assessed to be less than 20% Calibration timing Spreaders should be calibrated: Just before the start of the season Mid-season Whenever significant changes are made to the spreader (maintenance, repair, etc.) When salt type or condition changes Performance monitoring indicates a problem A concern is raised by driver Vehicle collisions along a route attributed to icy conditions. Page 26 Monitoring spreader discharge performance Once calibrated, spreader performance may change as a result of many factors Spreaders should be routinely monitored throughout the season Carry out re-calibration of spreaders where performance changes Incorporated as routine procedure, provides a quick and easy method of checking the spreader performance in terms of discharge rate Considerations for precautionary treatments Spreading capability and performance Forecast weather conditions Road surface wetness Traffic levels during and after spreading Page 27 Page 28 7

8 Weather & road surface conditions Spread rates are dependent on: The amount of water present at the road surface Road surface temperature Wind speed Traffic Levels Road surface wetness Definition Description Water film thickness (mm) Dry road Damp road Wet road A road that shows no signs of water or dampness at the surface but may be just detectably darker (however it may have moisture contained in pores below the surface that is not 'pumped' to the surface by traffic) A road which is clearly dark but traffic does not generate any spray. This would be typical of a welldrained road when there has been no rainfall after 6 hours before the treatment time. A road on which traffic produces spray but not small water droplets. This would be typical of a welldrained road when there has been rainfall up to 3 hours before the treatment time. 0 to 0.03mm 0.03 to 0.05mm 0.05 to 0.1mm Page 29 Page 30 Traffic levels Target Spread Rates: The guidance considers two levels of traffic: - Heavy vehicles per hour per lane or more - Low/Medium up to 250 vehicles per hour per lane Target spread rates for precautionary treatments Treatments for snow, ice and freezing rain Treatments for extreme cold Page 31 Page 32 8

9 Target spread rates for precautionary treatments The majority of winter service treatments in the UK are precautionary Sufficient salt should be spread to: - Prevent frost and ice formation - Prevent ice or snow bonding to the carriageway Spread rates should be kept as low as practicable for the forecast conditions and road surfaces considered - Cost savings - Increased resilience - Environment Target spread rates for precautionary treatments Latest revision of Appendix H contains new spread rate matrices for dry, pre-wetted and treated salt Based on: - Shared knowledge from expert practitioners - 12 years of knowledge from track and field trials of salt spreading - Research in the UK and overseas Tried and tested Provide the opportunity for authorities to make salt savings Page 33 Page 34 Target spread rates for precautionary treatments Spread rate decision based on assessment of 3 factors: Salt distribution Good/Fair/Poor Traffic level Low/Medium or High Salt loss immediately after spreading Normal or High Salt loss immediately after spreading The salt loss anticipated after spreading should be assessed as normal or high: Normal loss - Traffic is not heavy during spreading - Road surface is wet High loss - Traffic heavy during spreading and road surface dry or damp, or If the moisture content of dry salt is less than 2% when dry salting A flowchart is provided to guide the decision making process Page 35 Page 36 9

10 Weather and road surface conditions Road surface temperature (RST) ranges: At or above -2 C Below -2 C and above -5 C At or below -5 C and above -10 C For each temperature range: Dry or damp Wet New spread rate matrices New spread rate matrices provide - Minimum recommended rates - A reference point for review of current rates Based on assessment of spreading capability and network conditions: - Can provide an opportunity for salt savings from reduced rates - Can provide a warning for conditions where recommended rates are higher than current rates Spread rates greater than 20g/m² in some conditions Page 37 Page 38 New spread rate matrices TREATMENT MATRIX A DRY SALTING (De-icer spread rates in g/m 2 ) Frost or forecast frost Road Surface Temperature (RST) and Road Surface Wetness Column Cvrg Traffic Loss RST at or above -2 C and dry or damp road conditions RST at or above -2 C and wet road conditions RST below -2 C and above - 5 C and dry or damp road conditions RST below -2 C and above - 5 C and wet road conditions RST at or below -5 C and above -10 C *1 and dry or damp road conditions RST at or below -5 C and above -10 C *1 and wet road conditions A PC HT NL B PC HT HL C PC MT NL D PC MT HL E FC HT NL F FC HT HL G FC MT NL H FC MT HL I GC HT NL J GC HT HL K GC MT NL L GC MT HL Please see Table H13 for variations to the rates given above Treatments for snow, ice and freezing rain Impractical to spread sufficient salt to melt more than very thin layers of snow and ice It requires 40g/m 2 on the carriageway to melt 1mm of ice or 10mm of un-compacted snow at -2 C - Requires spreading at least 50 to 60g/m² Ploughing is the only economical, effective and environmentally acceptable way to deal with all but very light snow Page 39 Page 40 10

11 Ploughing Appendix H provides guidance on the types of plough and good ploughing practices Ploughing is most effective when down to the road surface (importance of suitable ploughs and blades) Treatment guidance Snow and Ice Guidance is provided in Appendix H for the following treatment scenarios: - Precautionary treatments before snow or freezing rain - Treatments during snowfall - Treatment of slush on the carriageway - Treatment of thin layers of ice (up to approximately 1mm) - Treatments of medium or thick ice and compacted snow Page 41 Page 42 Treatment types Table H14 Timing of treatments for snow and freezing rain Timing of treatment Treatment type Before snowfall and freezing rain Salt spreading During freezing rain, or where there are minor accumulations of ice During snowfall After snowfall When there is slush on the road After snowfall When there is compacted snow or ice on the road Salt spreading Ploughing Salt spreading Ploughing Salt spreading Ploughing Salt spreading Salt and abrasive mixtures Abrasives only Treatments for Extreme Cold Treatments used when: - The combination of temperature and humidity result in salt dissolving too slowly to be effective - The temperatures are so low that salt is no longer effective in melting or preventing ice forming Spreading salt when temperature less than: -7 C in normal humidity -5 C in lower humidity (<80%) When temperatures -15 o C or lower are forecast Page 43 Page 44 11

12 Frezzing point temperature ( C) Use of alternative de-icers for Extreme Cold Types of de-icer considered: - Magnesium chloride - Calcium chloride - ABP type de-icers blended with a chloride brine Alternative de-icers can be used as liquids on their own or in combination with salt For precautionary treatments in Extreme Cold, the liquid de-icers are best spread as the wetting agent in pre-wetted salt Use of alternative de-icers Solution concentration (%) NaCl MgCl2 CaCl Page 45 Page 46 Use of alternative de-icers Guidance includes - Storage - Spreading equipment - Spread rates - Treatment strategies - Environmental and corrosion considerations Consideration may be given to mutual aid and resource sharing within the winter plans of service providers Insert the title of your Thank presentation you and here enjoy the rest of the day Presented by Name Here Job Title - Date Page 47 12