UTILITY Technical Applications Bulletin Use of Compressed Air-Powered Excavation for Utility/Construction Work
Utility AirSpade® Technical Applications Bulletin Use of Compressed Air-Powered Excavation for Utility/Construction Work contributing authors Thomas C. Tremblay Craig M.
Utility AirSpade® Technical Applications Bulletin Use of Compressed Air-Powered Excavation for Utility/Construction Work March 2019 contributing authors Thomas C. Tremblay Craig M. Schoen With illustrations and standard construction detail drawings by STIMSON available online at www.airspade.com/utilityguide Published by AirSpade Division, Guardair Corporation.
Table of Contents INTRODUCTION 2 The Case for Soft Excavation 2 A Brief History 4 Highlighting Differences Between Dry and Hydro Excavation 6 Utility AirSpade Innovations and Features 8 Utility AirSpade Safety Features 12 Hazards & Hidden Costs of Home-Made Tools 13 STANDARD PROCEDURES 14 Pre-Excavation Checklist 14 Underground Utilities – A Crowded Picture 16 – Trenching 18 – Potholing 20 – Keyholing 22 Safe Practices When Excavating Around Utilities 24 ADDITIONAL CONSIDERATIONS
INTRODUCTION THE CASE FOR SOFT EXCAVATION When it comes to underground utility lines, what you can’t see can hurt you. The Common Ground Alliance (CGA), an association that promotes efforts to reduce damage to underground infrastructure, estimates there are over 20 million miles of gas, electric, water, sewer and telecommunication lines buried in the United States. That’s the equivalent of more than one football field length of buried utilities for every man, woman, and child in the nation.
UNDERGROUND UTILITIES DAMAGED 2017 UNDERGROUND UTILITIES DAMAGE EVENTS BY EQUIPMENT 2017 Vacuum Equipment 0.4% Grader/Scraper 6% Other Auger 5% 6% Other 9% Backhoe 32% Boring 8% Electric 8% CATV 10% Telcom 46% Hand Tools 14% Natural Gas 27% Trencher 29% While each incident has a unique set of circumstances and sequence of events, in all the above cases, hard excavation methodologies – excavation with augers, backhoes, or power tools – were used at the time of the strike.
A BRIEF HISTORY During the early 1960s, Brooklyn Union Gas Company first pioneered using a compressed air powered lance in conjunction with a vacuum truck as a better way to dig and reduce the costs associated with approximately 30,000 annual street openings for gas distribution pipe repair. Compressed air, or “dry excavation” to dig utility “potholes” proved to be a safe and reliable alternative to manual or mechanical methods of uncovering buried utility lines without damage.
In addition to uncovering utility lines, dry excavation was tested in several applications during the 1970s and 1980s. This included work with the Department of Defense to uncover landmines and unexploded ordnance, as well as “trenching” for construction. Improvements in equipment included advancements in AirSpade nozzle technology to provide faster excavation.
HIGHLIGHTING DIFFERENCES BETWEEN DRY AND HYDRO EXCAVATION High-powered, mobile vacuum units are essential pieces of equipment for safely locating and uncovering underground utilities. Their effectiveness is greatly enhanced when operating in tandem with either compressed air, or high-pressure water – techniques known as Dry Excavation and Hydro Excavation.
HYDRO EXCAVATION – ADVANTAGES Hydro excavation tends to be most effective with more compact soils including frozen surfaces. Onboard water heaters warm the water which aids in cutting through the soil. Water also acts as a lubricant and helps to prolong the life of vacuum equipment by reducing wear on vacuum hoses and other components in the air stream. Hydro excavation is especially useful for tank, pit, or general cleaning and does not produce the sandblasting effect common to dry excavation.
UTILITY AIRSPADE INNOVATIONS AND FEATURES As dry excavation has grown for underground utility applications, the need for a specialized tool to meet safety and other concerns has become more acute. Given the potential hazards and costs associated with excavation of underground lines, Guardair Corporation drew upon expertise from utilities across the US to design the Utility AirSpade. Their concerns included: More efficient usage of compressed air also reduces air compressor operating hours.
Retractable Stabilizer Bar Pressure Gauge l Utility AirSpade manufactured by Guardair Corporation Non-Sparking Bronze Threaded Coupling l Non-Conductive Fiberglass Barrel with Insulated Inner Air Hose l Non-Sparking Threaded Coupling l Ergonomic Grip l l l Adjustable Dirt Shield Cast Aluminum Handle Dead-Man Trigger l Non-Sparking Non-Sparking Bronze Supersonic Supersonic Nozzle Nozzle l l ll Trigger Guard with Generous Opening l 3/4” FNPT Inlet ELIMINATE POTENTIAL SPARKING HUMAN FAC
PROTECTION FROM HIGH VOLTAGES When excavating in the vicinity of underground utilities, the potential exists to uncover and expose high-voltage electrical lines. Consequently, to protect workers at the job site, the Utility AirSpade features an insulated fiberglass barrel assembly – incorporating a high-dielectric fiberglass outer barrel and an insulated inner air hose. Together, these components provide an electrical insulation rating of 75 kV per foot.
Introduction 11
UTILITY AIRSPADE SAFETY FEATURES Every Utility AirSpade is equipped with the following safety features: Dead-Man Trigger Drop a home-made air lance in the full-on position and it has the potential to “whip” and cause serious injury. The Utility AirSpade incorporates a dead-man trigger, which immediately shuts off the air supply if released. Lightweight Construction Home-made air lances made from heavy, iron pipe accelerate operator fatigue and that’s when accidents are most likely to occur.
HAZARDS & HIDDEN COSTS OF HOME-MADE TOOLS Utility companies and contractors are under pressure to control operating costs. With air compressors common on job sites, some work crews fashion their own air-powered excavation tools – in hopes of finding cheaper alternatives to safe, commercially available tools such as the Utility AirSpade. “Workers say, it’s only blowing air so we can make a tool for $100,” explains Craig Schoen, AirSpade National Sales Manager.
STANDARD PROCEDURES 4 o Pre-Excavation Checklist Before EVERY Excavation IN THE OFFICE JOBSITE DOCUMENTATION o Consult maps or field sketches of location. o Review all drawings, plans & engineering blueprints for existing o Post the One Call Ticket number at the job site. o Compare actual job site observations to One Call Ticket: buried facilities. o Call 811 at least 2-3 business days before excavation (check state One Call laws).
Standard Procedures 15
UNDERGROUND UTILITIES – A Crowded Picture Across the modern landscape, the proliferation of underground utilities has grown significantly as we have come to appreciate the improved visual aesthetics. While undergrounding is initially expensive, utility providers benefit from increased reliability and protection from the elements. However, the potential for service interruptions due to accidental strikes when uncovering underground lines for maintenance or during construction, is a growing concern.
High Voltage Power Lines: High voltage A/C power Water Main: Potable fresh water supply District Chilled Water: Dedicated institutional or municipal system Telecommunication Lines: Telephone, cable, and fiber optic lines District Hot Water/Steam: Dedicated institutional or municipal system Natural Gas: Gas for heating, cooling, cooking, and hot water Sewer Lines: Wastewater routed to sewage treatment plants Fire Hydrant Lines: Water for fire hydrants Specialized Vacuum Excavation Techniques Three primary
TRENCHING 18 Utility AirSpade Technical Applications Bulletin
Standard Procedures 19
POTHOLING 20 Utility AirSpade Technical Applications Bulletin
Standard Procedures 21
KEYHOLING 22 Utility AirSpade Technical Applications Bulletin
Standard Procedures 23
SAFE PRACTICES WHEN EXCAVATING AROUND UTILITIES OSHA 1926 Subpart P spells out safety requirements for excavation and trenching operations. These include measures to protect workers from cave-ins, falls, hazardous atmospheres, and underground utility-line strikes.
Standard Procedures 25
ADDITIONAL CONSIDERATIONS AIR COMPRESSOR BASICS SIZE Air compressors are sized by air pressure and air flow. In the US, pressure is measured in pounds per square inch (psi). Flow is measured in cubic feet of air per minute (cfm). Virtually all air compressors nominally operate at approximately 90 - 100 psi while air flow capacities vary from model to model -- from a few cfm for small electric piston units, to hundreds of cfm for gas or diesel driven portable screw compressors.
For example, increasing the compressor output pressure (by say 30 percent to 117 psi) increases the air-jet force and exit momentum flux (stress seen by the soil) but only nominally. Supplying higher pressure to a supersonic nozzle designed to work at 90 psi actually de-focuses the air-jet thereby degrading performance. In addition, operating the air compressor at higher pressures will dramatically increase energy (fuel) consumption.
AIR HOSE BASICS AIR HOSE AIR HOSE PRESSURE LOSSES The Utility AirSpade features a ¾” FNPT inlet equipped with ¾” Universal Coupling. To provide adequate air flow to the tool, Guardair recommends air hose no smaller than ¾”ID. Make sure the air hose is rated at least 150 psi and is operating within its temperature rating. Never exceed the air hose manufacturer’s specifications. See OSHA Standard OSHA 29 CFR 1926.302 (b) (5).
Additional Considerations 29
APPENDIX Appendix A: Call 811 Prior to starting any underground excavation always contact Dig Safe first. Dial 811 or contact the local (statewide) Dig Safe One Call Center (see adjacent tables).* STATE PHONE WEBSITE Alabama 800-292-8525 Al811.com Alaska 800-478-3121 Akonecall.com Arizona 800-782-5348 Arizona811.com Arkansas 800-482-8998 Arkonecall.com California NORTH 800-642-2444 Usanorth811.org California SOUTH 800-422-4133 Digalert.
STATE PHONE STATE WEBSITE PHONE WEBSITE Massachusetts 888-344-7233 Digsafe.com Texas 800-344-8377 Texas811.org Michigan 800-482-7171 Missdig811.com Utah 800-662-4111 Bluestakes.org Minnesota 800-252-1166 Gopherstateonecall.com Vermont 888-344-7233 Digsafe.com Mississippi 800-227-6477 Ms811.com Virginia 800-552-7001 Va811.com Missouri 800-334-7483 Mo1call.com Washington 800-424-5555 Washington811.com Montana 800-424-5555 Montana811.org Washington, D.C.
Appendix B: Soil Characteristics SOIL CLASSIFICATIONS STABLE ROCK Unconfined Compressive Strength by Rock Type The effectiveness of airspading largely depends upon the type of soil present.
SOIL TEXTURES OSHA Cohesive Soil Types (A, B, or C) can be identified by the texture of a given soil. Shown below on the left is the U.S. Department of Agriculture Textural Soil Classification Chart. This chart plots soil classification as a percentage of sand, silt, and clay and classifies each unique combination. The chart on the right contains the same information with OSHA Cohesive Soil Types superimposed.
Appendix C: Color Code for Marking Underground Utility Lines Electric Gas-Oil-Steam Communication CATV Potable Water Reclaimed Water Sewer & Drainage Temporary Survey Markings Proposed Excavation 1-888-DIG SAFE 1-888-(344-7233) digsafe.
Appendix D: Utility AirSpade Technical Specifications Utility Air Spade 4000 Technical Specifications Part Number: ASU4150G4 – 150 cfm Nozzle with 4 Ft.
Appendix E: Further Reading Common Ground Alliance, http://call811.com/before-you-dig/risk-reduction Stacy Cummings, “Do You Know What’s Below? Call 811 Before You Dig!”, U.S. Department of Transportation “Fast Lane” blog, Aug. 6, 2015, https://content.govdelivery.com/accounts/USDOT/ bulletins/1132ec1 National Transportation Safety Board, pipeline accident brief, http://www.ntsb.gov/investigations/AccidentReports/Reports/ PAB1302.pdf Washington State Department of Labor & Industries,http://www.lni.
Appendix F: Online Resources AirSpade Website AirSpade > Markets > Utility/Construction http://www.airspade.com/pages/utility-construction Common Ground Alliance DIRT Annual Report http://www.commongroundalliance.com/dirt OSHA Standards United States Department of Labor Occupational Safety and Health Administration http://www.osha.gov/law-regs.html This booklet is available to download as a PDF online at: www.airspade.
Glossary Airspading: Soil excavation techniques utilizing a proprietary compressed air-powered tool incorporating a supersonic nozzle. Approved Contractor: Operator with sufficient education, training, and experience in vacuum excavation and airspading. Backfill: Refilling the void created by excavation. CFM: Cubic Feet per Minute (cu ft/min). Measurement of the rate of flow of air passing through an orifice.
SCFM: Standard cubic feet per minute (SCFM) Flow rate of air corrected to “standardized” conditions of temperature and pressure. Soft Excavation: Excavation by dry (compressed air) or hydro (high-pressure water) in conjunction with a powerful vacuum. Slurry: Semi-liquid mixture of soil particles suspended in water. Spoil: Waste material including earth and rock uncovered during the excavation process.
Contributors and Bios Guardair Corporation Thomas C. Tremblay, contributing author President With a rich history dating back to 1942, Guardair Corporation is a world-class manufacturer of industrial/commercial pneumatic tools and accessories, including the AirSpade. In 1994, Tom led a group that acquired the company and has guided and grown the business since that time. Before Guardair, Tom was a Vice President at New England Capital, the venture capital arm of the Bank of New England.
Appendix 41
Utility AirSpade Technical Applications Bulletin Guardair Corporation STIMSON This booklet is available to download as a PDF, along with CAD details online at: www.airspade.com/utilityguide Division of Guardair Corporation 47 Veterans Drive • Chicopee, MA 01022-1062 Toll-Free: 800-482-7324 | Local: 413-594-4400 | Fax: 413-594-4884 Email: info@airspade.com • airspade.
