By Todd Teets, Safety Trainer (email)
Safety Management Group
Every few months, the media’s attention is captured by an all-too-familiar situation: a worker at a construction site is trapped in a trench. Puzzled TV viewers wonder what’s so dangerous about the situation, or why the local fire department can’t rescue the worker in seconds. After all, the trench doesn’t seem to be that deep.
A trench collapse in Anderson, Indiana, earlier this year illustrates the amount the equipment required for extrication.
But what the media and viewers don’t realize – and what the workers seem to have forgotten – is just how heavy dirt and other trenching spoils can be. The trapped laborer is all too aware of the intense pressure the situation is creating. If he’s fortunate enough to survive, he’ll face a long recovery from the injuries.
How much pressure? Consider that a cubic yard of soil may weigh more than 2,700 pounds – as much as some cars. Even a chunk of dirt the size of a washing machine may weigh as much as 1,500 pounds. In addition, because soils tend to be very dense, suffocation is as great a hazard as the weight of the material. There are also the risks involves with water and toxic fumes.
No wonder that OSHA reports excavations involve a fatality rate that’s 112 percent higher than that for general construction activities. What makes that rate even more chilling is that most trenching accidents can be prevented. Following some very basic safety procedures can minimize the possibility of a trench accident, or, should an accident occur, can reduce the amount of time and effort needed for a rescue.
1. Know the risk. Any kind of excavation is a potentially dangerous worksite, because of the instability of the materials involved. In addition to the danger of collapse, workers in trench situations may also be exposed to toxic materials that have been unearthed, drowning because of water that fills the trench before the worker can escape, and the possibility of suffocation when adequate oxygen cannot penetrate the soil, spoils, or other materials.
2. Study before digging. Every trench project is different, so identifying the specific risks at the site is critical. An individual with specialized training in trenching safety should inspect the site carefully and determine the condition of and challenges associated with the soil that will be handled. The site review should also examine whether there are utility lines or pipelines that might be in close proximity to the site, the potential impact of underground storage tanks, if traffic on adjacent roads might increase the instability of the surrounding soil, and the possibility that water from nearby ditches or a sudden rainstorm could unexpectedly fill the trench. The exact location of utilities must be determined by hand digging or by the use of a probe. Utility company locates are often inaccurate, despite their best efforts (older utilities do not lend themselves to easy identification).
3. Plan for the risks. OSHA regulations state that protective systems must be in place before digging can begin. That includes everything from determining how to handle traffic hazards, to testing for fumes and gases caused by equipment in or near the trench, to providing ventilation and any needed respiratory protection. A particular site may demand shoring materials or trench boxes to protect the workers.
4. Provide and protect access. Safe access to and from the trench is critical, particularly when a cave-in, injury, or other emergency occurs. Workers must be able to escape quickly in event of a cave-in, water incursion, or hazardous materials incident. These requirements apply whenever the potential for entry by employees exists, even if for just a moment. If the trench is at least four feet deep, OSHA regulations call for proper egress within 25 feet of all workers, whether that involves ladders, stairs, or a ramp. That egress must be designed by someone with the proper training, and the integrity must be ensured so that components of the egress will not be separated in the event of an incident. The egress must also ensure that workers will not be subjected to additional injury risks when escaping the excavation. There are additional hazards regarding structural integrity for access/egress of vehicles entering/exiting the excavation as well, so ramps used by them must be designed by a person qualified in structural design.
5. Be ready to rescue. The safety plan should include a complete rescue plan that addresses how workers should respond in a variety of situations. For example, the response that would be used in a cave-in will be very different from that required if a worker suffers a heart attack while in the trench. It’s important that workers understand the rescue plan, because the wrong response can exacerbate a difficult situation. A worker rushing in to free a trapped counterpart may result in both of them becoming trapped. The rescue plan should also address who will brief and coordinate with the fire department and other outside rescue personnel that respond to an incident.
6. Pay attention to spoils. It’s easy to think of excavated material as nothing more than a pile of dirt, but the weight and fluidity of a spoil pile can create its own set of hazards. First, spoil piles must be placed far enough from the excavation so that they don’t fall back into the trench, cause the sides to cave in, or create a situation in which equipment can roll into the trench. Generally, spoil piles should be kept at least two feet from the trench, and retaining devices should be used to keep spoils from falling in. If there isn’t enough room to store spoils safely at the site, they should be hauled to a temporary location elsewhere.
7. Never stop inspecting. An excavation site is not static. Every time a load of soil is removed or a piece of heavy equipment rolls near the edge of the excavation, it changes the integrity of the site. That’s why it’s important to inspect the site at the beginning of each shift, or any time an action increases the hazard to workers (such as an earthmover moving too close to the trench). The site should also be inspected during and after rain events, or when freezing weather creates slip and fall hazards. Simply having a laborer look around isn’t adequate. The person who is inspecting the site should have training in both soil analysis and the proper use of protective systems and strategies, and those excavations 20 feet deep or more require protective systems designed by a qualified engineer.