Quoting from a recent OSHA (Occupational Safety and Health Administration) Fact Sheet seems a good way to introduce the topic of trench safety.
“Excavation and trenching are among the most hazardous construction operations. OSHA defines an excavation as any man-made cut, cavity, trench, or depression in the earth’s surface formed by earth removal. A trench is defined as a narrow underground excavation that is deeper than it is wide, and is no wider than 15 feet. Cave-ins pose the greatest risk and are much more likely than other excavation-related accidents to result in worker fatalities. Trench collapses cause dozens of fatalities and hundreds of injuries each year.”
More Information on Trench Safety
Contractors who send workers into trenches have a legal obligation to ensure the safety of those workers, either by complying with the OSHA standard for excavations—Part 1926/Subpart P/Sections 1926.650-652—or with applicable state standards. The OSHA standard address all aspects of trench safety, including protecting workers from trench collapse (cave-in), safe access/egress, hazardous atmospheres, adjacent-structure stability, and the requirement for an on-site “competent person,” who “must be able to identify hazards and must have authority to take appropriate corrective action.”
Compliance with the provisions of Subpart P is, however, not universal among excavating contractors.
“A review of recent trenching violations would suggest that compliance to the standard, now in its 26th year, is still less than 50 percent,” says Wendell Wood, an excavation-safety consultant and trainer with 40-plus years in the industry. “Failure to provide a protective system and failure to properly handle spoil [which must be at least 2 feet from the trench] remain top citations. Trench-access/egress provisions continue to be violated, as are provisions requiring a competent person to daily inspect the excavation and its protective system.”
More recently, says Wood, failure to provide awareness training for new hires is of increasing concern. “New employees might find themselves immediately at the bottom of a trench,” he says, “with no idea of the multiple hazards they face.”
As the OSHA Fact Sheet noted, trench collapse is among the principal hazards facing workers—thus Subpart P’s requirement (section 1926.652) for a protective system. Three basic types of protective systems are covered in the standard: shielding (devices designed to protect workers in the event of a collapse, such as trench boxes); shoring (bracing designed to prevent collapse, such as hydraulic shoring or slide-rail systems); and sloping or benching trench walls away from the trench bottom at a safe angle.
OSHA gives a pass on trench protection only in two instances: 1) when “excavations are made entirely in stable rock” or 2) when “excavations are less than 5 feet in depth and examination of the ground by a competent person provides no indication of a potential cave-in.”
Sloping/benching is permissible for excavations less than 20 feet deep, with the angle of the slope or bench determined by soil type, whether A, B, or C. (See Subpart P, Appendix A and B for details.) The less stable the soil, the shallower the angle. Sloping/benching for excavations deeper than 20 feet must be designed by a registered professional engineer.
Some contractors make the point that sloping trench walls can involve moving a significant amount of extra material that must be stockpiled and excavated a second time when backfilling; they advise considering the economics of doing so against the cost of alternative protective systems, assuming that safety is equally addressed with all the viable options.
Mike Ross, national training director for Efficiency Production, a manufacturer of trench boxes and shoring systems, makes the point that OSHA’s Subpart P is a performance-based standard, giving the competent person parameters to follow, rather than specific directives.
This means, he says, that the competent person can select the protective system best suited to site conditions, as long as the competent person can demonstrate the safety of the system upon request—and can show that the system is being used in accordance with the system manufacturer’s tabulated data. (Tabulated data include tables and charts, approved by a registered engineer, that govern the use of a particular system.) For instance, a particular trench shield might be rated safe for use to depths of 8 feet, but using it at 15 feet exceeds limitations stated in the tabulated data and places workers at risk.
“Probably 80 percent of all projects can be handled with trench boxes,” says Ross. “This is usually the fastest method of placing pipe. When a box can’t be used, then you choose the best alternative, whether slide-rail, sheeting frames, or hydraulic shores. The choice is dictated by the project and site conditions.”
Jim Mclaughlin, safety officer, field, for William A. Hazel, Inc. a site-development and road-construction contractor in northern Virginia, notes some of the considerations involved when selecting a protective system.
“The work area primarily dictates the type of trench safety actions we take,” says Mclaughlin. “Is there adequate space to slope the sides of the trench to 1½ to 1? What type of soil is encountered? Are utilities or other obstructions present that would prevent sloping or use of a trench box? Will the work take place near a roadway? These are some of the considerations regarding trench safety.”
Safety consultant Wood notes that Subpart P requires that underground utilities be removed, supported, or protected, as necessary. “Some contractors will use a shield in these situations, because that’s what they normally use,” says Wood. “A shield, however, unless used with great care, might not provide proper support of the utility. In these instances, a soil-support system that is actively holding soil in place and not allowing it to move out from under a parallel gas or water line might be the best way to meet the OSHA requirement.”
Other cautions to be observed when using trench shields, says Wood, is to avoid over-cutting and allowing the shield to move laterally in the trench—and also to avoid allowing material to spill over the top of the shield by leaving a vertical wall above the shield.
Jay Goff, safety director for the Hazel company, lists other non-negotiable safety procedures the company has in place. “We require a valid ‘miss utility’ ticket for the work area with all utilities properly marked. Marked utilities are test-pit located and exposed prior to excavation. A competent person must be on site to ensure that OSHA laws and company policies are enforced.”
In Wood’s opinion, the selection of a competent person is a primary safety consideration on any excavation project. “Contractors should make a concerted effort to designate a competent person who has the experience to assess the job site and surrounding areas with an eye to potentially hazardous situations. It’s a mistake, in my opinion, to place this responsibility on whoever is willing to accept it. In my experience, only a small segment of typical work crews has the force of character to take action when they see something unsafe.”
If the competent person is called away from the site for whatever reason, says Wood, the contractor should have designated another member of the crew to be ready to step into the role. “If such provisions are not in place,” says Wood, “the competent person must have the courage and authority to stop work until someone with the required experience is available. A company really should have procedures and protocols in place to handle these situations.”
When Construction Equipment asked Wood to identify other areas of trench safety that the competent person must keep in view, he noted hazardous atmospheres. Subpart P, section 1926.651(g), addresses air quality in excavations, and refers the competent person to 1926 Subparts D and E, which cover environmental controls and personal-protective and life-saving equipment. In some instances, air-quality testing is required before workers can enter an excavation, and respiratory protection or ventilation might be required.
“[Hazardous atmospheres] have not been a focus on the part of compliance officers,” says Wood, “but I think it will become an issue in the coming months with the publication and now enforcement [August 2015] of the new Confined Spaces in Construction standard.”
Although the scope of the new standard, 1926 Subpart AA, officially exempts construction work regulated by Subpart P, some think it might have implications that excavating contractors should keep in mind, especially if in the course of their work confined spaces are created, such as manholes.
Wood also encourages excavating contractors to establish a policy of ongoing training for those employees who work in trenches.
“Training—not just when it’s convenient, but continuous training for all, with the participation of management, and in a language that workers understand—is the single best asset for developing a culture that communicates a genuine desire to have safe work sites. Such a culture demonstrates to employees that safety is simply not lip service, but is instead a priority, motivated by doing the right thing for employees.”
Companies that practice this principle, says Wood, have discovered that it produces a stable, dedicated work force that works productively and profitably.