Although there are some ongoing issues about using trenchless methods in some parts of the country, the demand for trenchless technology to rehabilitate and expand underground utilities still exists. Trenchless technology reduces employee exposure to many hazards associated with open-cut excavations. However, trenchless operations have their share of hazards that must be controlled or eliminated.
Similar to open-cut trenches or excavations, a properly trained competent person must oversee the operations to ensure safety. The competent person must be trained and knowledgeable about the excavation standard, soil analysis and protective systems as they apply to trenchless operations. Although trench safety requirements are similar to open-cut requirements, some hazards are specific to trenchless jobsites. This article will identify some of the hazards associated with trenchless operations.
Applicable Safety Requirements
The employer must ensure that all the applicable requirements of the OSHA excavation standard are met. In addition, contractors should follow the safety recommendations provided by the machine manufacturer. See the operator’s manual for the make and model of the trenchless equipment that is being used to perform the operation.
For example, a protective system (shoring, shielding, sloping) is required to protect workers from a cave-in in excavations such as a horizontal auger boring pit greater than 5 ft deep (in some states 4 ft). In addition, a safe means of getting in and out of the excavation must be used; spoils, materials, equipment and tools must be set back at least 2 ft from the edge of the excavation; water must be controlled; personal protective equipment must be provided and used; and the potential for a hazardous atmosphere must be monitored.
Before starting the job, the competent person must determine the soil type. In most cases when boring and jacking, the soil should be considered a type “C” because of the amount of vibration created by the machinery, cranes, other equipment or traffic located near the pit. Like any other trenching operation, if the competent person classifies the soil as anything other than a type “C,” they must be able to demonstrate to a compliance officer the method(s) used to make that determination.
Selecting a Protective System
When excavations such as a boring pit are needed, a contractor can use any type of protective system, such as trench boxes or engineered systems. In some situations, it is necessary to provide a system with closed ends to prevent the ends of the trench from caving in. The contractor should check with the manufacturer of the protective system or an engineer to determine how the ends of the system (i.e., boring box) can be closed without affecting the system’s stability and/or strength. After careful consideration of the effects of vibration on soil stability, sloping may be used. However, sloping requires a large excavated area, which is generally not available in areas where trenchless methods are commonly used. In fact, trenchless methods are often chosen due to limited space and the need to limit disruption to the surrounding area. No matter what method is employed, workers must be protected from a cave-in.
Another major consideration that will affect soil stability and protective system selection is the placement of cranes and other equipment. The type, location and weight of the equipment must be considered when selecting the protective system. For example, has the protective system been designed to withstand the additional lateral loads created by the weight of the equipment?
The pit must be large enough to include the boring or jacking equipment and space for workers to move around the equipment safely. Every pit should include a safety zone where workers can stand clear of loads hoisted into or out of the trench. Where large boring equipment or pipe blocks access to ladders, it may be necessary to allow enough room for a ladder on both sides of the excavation.
Directional drills are set above ground and don’t require a boring pit. However, when receiving pits are used, the excavation standard still applies. Directional drilling rigs are generally very safe as long as they are properly protected from electrical hazards and guards are in place.
Workers must stay clear of rotating augers, pipe and the head of the machine. Workers must not wear loose clothing, jewelry (such as necklaces and rings) or long hair around the machine because they can get tangled in the rotating parts. Loose fitting gloves can also be a problem.
Straddling, stepping over or stepping on the auger or shaft can lead to serious injuries. When connecting and disconnecting pipes or augers, using the machine’s rotation should only be done when permitted by the manufacturer and then only at very slow speed. The safest method is to use pipe tongs that are designed for the purpose.
The equipment operators should never leave the controls for any reason while the machine is in operation. The throttle should never be locked or blocked in the on position, and the operator must always be in control of the machine. The operator must watch out for other workers and shut the machine down if any worker is in danger.
Work zones are frequently located in areas where it is very important to ensure the safe movement of vehicles and pedestrians around the work zone. Traffic control, in the form of barricades, fences and/or flaggers, must be carefully considered and implemented. The possibility of someone falling into a pit or getting too close to a machine is a potential hazard that must always be considered.
OSHA standards require guardrails or barricades around open pits to prevent people from falling in. Standard guardrails with toe boards, raised trench box walls, attachments or sheet piling can reduce the fall hazards.
OSHA does not require a fence or barricade around a direction drill, therefore it is important to consider blocking off access to the machine and only authorized people should be permitted into these areas. The safest practice is to keep everybody clear of machines and excavations except for personnel who need to be in the area.
Crane and Excavator Safety
Lifting and hoisting materials and equipment with cranes requires knowledge of safe crane operations and rigging. Crane and excavator operators should be licensed or qualified to operate the type of machine in use. Personnel responsible for rigging should also be trained and qualified to perform rigging tasks.
Improper rigging methods and overloading can cause a sling or cable to break, which could lead to injuries or damage to materials and/or equipment. Tag lines should be used when necessary to control load swing and movement.
Auger boring pits can contain a hazardous atmosphere due to the equipment used in the pit to push or pull the mole, auger, pipe, etc. A hazardous atmosphere may also be encountered due to the exhausts from vehicles, cranes, excavator or other equipment or from gas pockets disturbed by the operations. Contractors must ensure that the atmosphere within the pit is monitored with a gas monitor and is safe to work in. If oxygen levels are low, flammable gases are encountered or toxic materials, such as carbon monoxide or hydrogen sulfide, are above safe levels, the work should be stopped until the situation can be rectified and made safe.
Contractors and the assigned competent person have a responsibility to provide workers with a safe place to work. Trenchless technology operations can be safe, but they do require proper planning, use of the appropriate equipment and knowledgeable, properly trained workers.
George Kennedy is NUCA’s vice president of safety.