Next time, before you descend into a trench or another man-made cavity in the earth, you might want to consider the following numbers in gauging your odds of climbing back out unscathed should the walls cave in:112: This number represents the percentage increase in the fatality rate for excavation work compared to general construction work, according to the United States Department of Labor’s (DOL) Occupational Safety and Health Administration (OSHA).114: This is the weight, in pounds, of a typical cubic foot of dirt. That works out to more than 1.5 tons/yd.3 and is similar to the weight of a pickup truck. A load like that lying on top of you is more than enough to prevent your lungs from expanding.3: This is the number of minutes before you will suffocate if buried by dirt. In fact, very heavy soils can crush your body in a matter of seconds.Such numbers help explain why excavating is one of the most hazardous construction operations. According to one estimate, the number of fatalities from trench cave-ins in the US could be as high as about one a day, in addition to some 1,000–4,000 people injured each year in these accidents.A trench is unstable from the moment you start digging. Trench walls can collapse quickly, without warning. The risks of cave-ins increase as the trench deepens and the soil gets wetter or looser.What’s more, the likelihood of a second cave-in increases about 500% after a wall collapses. The threats include crushing, suffocation, loss of blood circulation, the collapse of nearby structures, and being struck by dirt, rocks, and other material that can fall or roll into a trench. Other hazards can be just as lethal to workers trapped in trenches. They range from fire and drowning to toxic fumes from nearby gasoline-driven equipment, dirt contaminated by leaking lines or storage tanks, and electrocution or explosions when a worker or equipment contacts underground utilities.Beyond the NumbersThese numbers, however, don’t tell the whole story. A variety of equipment and techniques are available to protect life and limb when working in trenches. They’re not only a good idea, but federal regulations (OSHA 29 CFR, Part 1926, Subpart P, July 1997) require contractors to follow certain procedures and practices when working in trenches. Besides, depending on your approach, these safety practices also can improve your profit prospects.Trench protective systems and practices are remarkably effective when used properly. “In my 21 years of experience, I’ve seen them save lives,” says John Newquist, a DOL team leader in North Aurora, IL. “In fact, I’ve never seen anyone die who has complied with trench safety rules.”Around the country, however, compliance with these rules is less than complete, say experts.“Our biggest challenge is convincing contractors to use protective systems when trenching,” says Tom Coble, president of Coble Trench Safety in Raleigh, NC, which sells and rents Speed Shore trench shoring equipment and protective systems to contractors in the Mid-Atlantic market. “The larger contractors tend to be very compliant with the regulations. But in the case of many smaller contractors, all we can do is explain the capabilities of our products for protecting workers against cave-ins and hope that the contractors use them.”Industry observers attribute the reluctance of some excavating contractors to use protective equipment and practices to various factors, including ignorance, apathy, and a desire to minimize construction costs.Keith Lamberson, president of Buford, GA–based Trench Shoring Services, a manufacturer and renter of trench-protective equipment and systems, offers this perspective on the economics: “Depending on type and size, our trench boxes rent for about $35 to $70 a day. Are you willing to risk injury or death to save that money? If that’s not convincing, consider the money you save with a trench box by not having to slope a trench wall. You can’t excavate or backfill a sloped wall for $35 to $70 a day.”
“Some contractors believe that a cave-in won’t happen to them,” says Mike West, engineering manager with Efficiency Production Inc., a manufacturer of trench shield and shoring systems in Mason, MI. “But would these same guys be willing to put their kids in an unprotected trench?”“Some contractors fail to appreciate the hazards of trenching because they themselves haven’t been hurt,” adds Newquist.He reports three 2003 cases in which inspectors from his office and a neighboring DOL office evacuated workers from trenches just minutes before the sides caved in.Sometimes, Newquist points out, the protective equipment contractors have on a site isn’t suitable for the job at hand. “For example, a contractor may have a trenching box to protect workers when installing a manhole, but the trenching box may be too small for the manhole. So, rather than stop work while waiting for a bigger box or installing a different protective system, the contractor will install the manhole without any cave-in protection.”In 2003, it took a rescue team more than seven hours to recover the body of man who was killed when one side of the trench, in which he was repairing a water line without any shoring protection, collapsed in one piece on top of him. Earlier in the week, a trench box had been used to support the trench walls; however, on the day of the cave-in, the box was not in place.Newquist reports that in Illinois, from October 2001 through September 2002 (the latest figures available), lack of cave-in protection ranked second on the list of the top 10 most-cited construction-site violations and totaled more than $350,000 in penalties. Lack of fall protection from scaffolds, roofs, or residential construction sites was the top violation.“Sixteen percent of these were repeat violations,” says Newquist. “The inspected company has been cited for the exact same violation or hazard during the past three years.”Among the reasons given by contractors for failing to comply with trenching and other construction-site safety requirements, he notes these:“The job was only going to take a minute.”“We have been doing this work for 20 years and would not expose ourselves to hazards” (said at the time an employee was in a 10-ft.-deep trench without cave-in protection).“The soil was good.”Costly NoncomplianceA sampling of trenching-accident investigations by OSHA reveals how trenching activities can turn deadly when protective measures aren’t in place:Failure to inspect the trench. A worker installing forms for a concrete footer in a 7.5-ft.-deep trench through loose, sandy soil was killed when the sides caved in. The trench was not inspected as required before the shift started work.Unsafe spoil-pile placement. One employee was killed and another suffered back injuries when the unprotected vertical walls of an 8-ft.-deep trench collapsed as the workers were installing a sewer pipe. A spoil pile had been placed on top of one side of the trench. In addition, a backhoe was parked on top of this pile. Investigators reported that the superimposed load of the spoil pile and backhoe might have caused the wall to collapse.Unsafe egress. Two workers were laying pipe in a 15-ft.-deep trench, which was not shored or sloped properly. While climbing the backfill—the only way to exit the trench—one of the employees was trapped by a small cave-in. While the second employee tried to excavate him, a second cave-in occurred, killing the first worker and injuring the second.Even without accounting for the horrific personal impacts of deaths and injuries, cave-ins can be extremely costly. Chris Musser, vice president of Downey, CA – based Trench Plate Rental Company, which provides shoring systems and produces Quick-Shor trenching products, lists some of these consequences:Costly repairs. Repairing existing utility lines or infrastructure damaged by improper trench support can be very expensive. Neighboring property can be damaged. Improper trench support can destroy adjacent streets, curbs, and sidewalks and undermine adjacent foundations, all of which can lead to expensive claims.Higher insurance rates. “Workman’s Compensation premiums are based on your three-year experience modifier,” Musser says. “Accidents or fatalities can easily increase your company’s insurance costs by more than 100%.”Heavy fines and legal expenses. OSHA fines start at $7,000 and can escalate rapidly from there. In 2003, for example, OSHA proposed an $83,300 penalty against a Texas contractor for failing to protect workers from trench cave-ins and exposure to carbon monoxide and a $99,400 penalty against a Louisiana contractor for not protecting employees from potential trenching and excavation hazards. In addition to legal fees, you could even face jail time for ignoring trench safety regulations.A Profitable BonusIn addition to improving safety, trench shields and shoring offer another important benefit: increased production.“They’re one of the few construction products that enhance both safety and production,” says West.In fact, he reports, when his company introduced the first commercial trench shields in 1971, there were no federal regulations concerning trench safety. The goal then was to improve production and reduce costs by using narrow-trench technology to eliminate the need for sloping to prevent cave-ins.“By digging a trench with straight instead of sloping sides, you excavate a lot less dirt and reduce the amount of backfill, compaction, and restoration,” he explains.Protective SystemsOSHA regulations are designed to reduce risks by requiring proper protective systems and procedures when excavating trenches, except when made entirely in stable rock. To prevent cave-ins of 5- to 20-ft.-deep trenches, OSHA requires one of three protective measures: sloping and benching, shielding, or shoring and sheeting. Responsibility for determining which system is best for any given job falls to project planners and the competent person on-site. A competent person is one who can identify existing and predictable hazards or hazardous or dangerous working conditions and who has the authority to take prompt corrective measures to eliminate or control them.For excavations deeper than 20 ft., the protective system must be designed by a registered professional engineer.For trenches less than 5 ft. deep, OSHA does not require a protective system, unless the competent person sees signs of a potential cave-in. Still, as Newquist cautions, “A wall collapse in a 4.5-foot-deep trench can still have serious results.”Sloping and BenchingThis approach protects against cave-ins by cutting the trench walls at such an angle that there is little chance of collapse. Termed the maximum allowable slope, it varies with type of soil, environmental conditions of exposure, and application of surcharge loads. In many cases, lack of available space, such as close proximity to utilities and traffic when trenching in a right of way, might prevent use of this approach, notes Newquist.“If you’re excavating an area that has been disturbed previously, such as a right of way, the soil is likely to be classified as C,” he says. “With Type C soil, the walls of the trench must be sloped back on each side of the excavation 1.5 feet horizontally for every 1 foot of depth.”Type of soil also determines the horizontal-to-vertical ratio of benched sides. Generally the bottom vertical height of the trench must be no more than 4 ft. for the first bench. Subsequent benches may be as high as 4-ft. vertical in Type A soil and no higher than 4 ft. in Type B soil to a total trench depth of 20 ft.ShoringShoring systems, whether timber, mechanical, or hydraulic, prevent movement of soil, underground utilities, roadways, and foundations by supporting the face of the trench. These systems include sheeting, which is driven into the ground and usually is used for long-term protection, and aluminum hydraulic systems, which are lightweight, reusable, and installed and removed from above the ground and pneumatic shoring.ShieldingUnlike shoring, a shield doesn’t prevent a cave-in. It instead protects workers inside the structure on which the trench walls collapse. It can be a permanent structure or, in the case of a trench box, a portable one.“A trench box is an excellent choice when placing continuous installations like pipe laying,” says Newquist. “You place the box in the trench and drag it along as the work progresses.”Although they normally are used in open areas, trench boxes also can be used in combination with sloping and benching.When using a trench box, Newquist suggests keeping workers out of the box and aboveground when moving the shield to prevent personnel from getting caught between the box and fixed objects. The excavated area between the outside of the trench box and the face of the trench should be as small as possible. The top of the shield should extend at least 18 in. above the level of any material that could fall or roll into the trench. Stack only shields designed for that purpose. Don’t stack shields from different manufacturers, since they might not be compatible. After positioning the box, backfill the space between the box and the trench walls with excavated material. Otherwise a cave-in could push the box sideways, creating a crushing hazard.“It’s important to remember that workers are protected from cave-ins by shielding and shoring only if they stay within the confines of the system,” Newquist points out.OSHA regulations also address placement of spoil. To prevent temporary spoil from falling on employees in a trench, it must be placed no closer than 2 ft. from the surface edge of the excavation, as measured from the nearest base of the spoil to the cut. Spoil should be placed so it channels stormwater and other runoff away from the excavation. Permanent spoil should be placed some distance from the excavation. If the spoil isn’t placed far enough away, it could cause the excavation to be out of compliance with the horizontal-to-vertical ratio required for a particular trench.A Big SelectionAt one time, sloping and timber shoring were the only choices for protecting workers from trench cave-ins. Today manufacturers offer a wide variety of standard and custom-made products to provide a safe working environment for just about any trenching or excavation job—from vertical and horizontal shoring to manhole boxes and tank pits.“Pre-engineered systems allow you to place shoring and shielding products into an excavation before workers enter a trench,” says Musser. “These modular shoring and shielding systems eliminate the guesswork and cost of custom engineering and put the savings in your pocket. They make installation fast and easy, without cutting, welding, nailing, or other expensive and time-consuming methods.”ShoringAluminum hydraulic shoring offers a fast, simple, economical and safe way to brace vertical trench faces. Designed for use in more stable soils, they’re available in up to 24-ft. lengths and are available in sizes to fit up to 12-ft.-wide trenches. They are installed by hand aboveground and can be stacked for different trench depths.Speed Shore’s Shoring Shields combine the benefits of aluminum hydraulic shoring with the solid-wall security of a static shield. Built with high-strength aluminum alloys, they are designed for utility maintenance and repair, cable splices, pipeline bellholes, vault placements, trenchless-technology pits, and light utility installations. The company reports that the solid-sheeted exterior provides optimum personnel protection while the lightweight design allows it to be handled with a rubber-tire backhoe.Efficiency Production’s shoring products include horizontal walers, which can be used in deeper excavations than vertical shores can and which provide a greater working area than vertical shores do. The company also produces a shoring system that features a clear span of 50 x 50 ft. and a 30-ft. depth.Slide-rail systems feature steel panels that slide into tracked rails as dirt is excavated and can be installed by a small crew with an excavator. They offer an easier, faster, and less-expensive alternative to conventional tight-sheeting/piling, especially in poor soil conditions and on sites adjacent to structures or utilities. They can be configured for linear, square, or rectangular excavations to depths of 30 ft. or more for such uses as pipelines, pits, retaining walls, and bridge abutments.Originally developed in Europe years ago, slide-rail systems are becoming more popular in the United States. Those made by American manufacturers feature heavier-duty components than European systems do, notes West. “The use of slide rail systems has really taken off in the US in the last 5 to 10 years, as the need to repair infrastructure in tight urban sites has increased. Contractors are finding that they can install our systems for about half the price of conventional steel sheeting.”ShieldingTrench boxes, installed aboveground, are available in both steel—installed using a crane or an excavator—and lightweight aluminum versions, which can be handled with a rubber-tire backhoe or a light excavator. Depending on manufacturer and model, features might include replaceable push blocks, double- or single-wall construction, cutouts for incoming utilities, and high-clearance spreaders for greater pipe clearance.The selection includes Trench Shoring Services’ steel trench boxes, which vary in size from a single-wall, 1,500-lb., 2-ft.-high x 12-ft.-long model to a double-wall, high-arch system that measures 12 ft. high x 16 ft. long and weighs 24,950 lb.Quick-Shor’s Quick-Box, an aluminum hydraulic trench box, can be moved and installed with a rubber-tire backhoe. Designed for smaller projects, it can shore up trench walls to a depth of 20 ft. It includes a wheel kit to support moving operations. The width adjusts hydraulically, and cylinders and return sleeves are protected by steel oversleeves. The stackable boxes can be used in three- or four-sided configurations and include doors to accommodate crossing utilities.Other EquipmentOther choices include Trench Shoring Services’ multisided cofferdams and manhole boxes and doghouse shoring panels to allow for pipe clearances on one to four sides, including three-way utility junctions and jumbo spreaders for connecting steel panels while allowing for rebar clearance, or to create pipe clearances in the middle of stacked panels.Regardless of features, OSHA requires that all protective systems have a manufacturer’s tabulated data sheet. This must include tables, charts, and other information, approved by a registered professional engineer and used to design and construct the protective system.Product Selection TipsSelecting the right equipment for a given job is a matter of matching product capabilities and features to site conditions and job requirements. For example, these systems offer such choices as a variety of spreader lengths to accommodate different trench widths, spreader height adapters for working with different-diameter pipes, and end panels. That’s one reason why more and more excavating contractors are renting rather than buying the equipment.“Renting allows you to choose the most precise solution to a shield or shoring problem,” says Lamberson. “The trench box you bought with 4-foot spreaders may be just fine for laying a 24-inch sewer line. But if your next job involves installing an 8-inch water line, you’ll have to overexcavate the trench to use that box. Renting offers a more affordable way to get the equipment that best fits the job.”“If you own a shielding or shoring system that you’re not using, it becomes a dead asset,” adds Coble. “Also, if you use it infrequently, you may lose track of the paperwork required by OSHA.”Still, owning trench shoring and shielding systems can make sense for contractors who do a lot of similar, long-term excavation projects and have the ability to store and transport the equipment, say experts.To meet OSHA requirements, the products of one manufacturer are similar to those of another in terms of engineering standards. “The differences between one brand of shield or shoring tend to be minor,” says Musser. “But depending on the job, those small differences can make a significant impact on productivity.”For example, he points out, the location of lifting or pulling points on a trench box can make a big difference if it doesn’t fit your equipment or work methods. “Not all boxes are designed to be pulled through a trench,” he explains. “Even if it is, one customer may prefer pulling the box with a cable or chain, another may use a custom pulling tongue, while a third may drag the box with an excavator bucket. For most production, the box should fit the way you move it.”Most manufacturers offer classroom training to help employees meet OSHA’s competent-person requirements. Typically this training covers such topics as OSHA standards, recognizing hazards and safety violations, soil classification and selection, and correct use of protective systems.Lamberson sees a clear need for this and other educational efforts. “Contractors can learn about the various protective equipment at trade shows and demonstrations provided by manufacturers and dealers. More excavating contractors need to make shoring and shielding a higher priority and learn more about it.”
