Ensuring Trench Safety And How Protective Systems Can Help
Trenches in construction sites are prone to many preventable accidents and fatalities. To keep workers safe from a trench collapse, employers must determine when and where protective systems are required and monitor their condition through daily inspections and maintenance. This is even more important if the work site conditions change constantly. Read on as we delve deeper into protective systems and how to determine which type of system is best for a given situation. When is a protective system necessary? OSHA excavation standards are detailed in length in CFR 1926, Subpart P. In essence, it states that organisations must always be extra careful and have a competent person determine whether using cave-in protection is required or not. This person is essentially someone who has the capacity and authorisation to identify and rectify predictable and existing hazards in the work environment or working conditions that are hazardous or unsanitary to employees. Two of the most important considerations when conducting underground work include identifying whether the excavation is less than 5 ft deep and the soil classification. OSHA states that all excavations exceeding a depth of 5 ft will require protective systems approved and designed by a professional engineer. That said, it is an industry practice to consider some form of protection regardless of how deep a trench is. Once it is verified that an excavation needs a protective system, the next step is to determine which system to employ. Determining the type of protective system for your trench Your choice of protective system will largely depend on five factors: excavation depth, type of soil, water content in the soil, weather and climate, and other ongoing operations in the vicinity. Soil classification covers four basic types: Type A, Type B, Type C, and stable rock. The first three are similar in that they are cohesive soils, with their main difference being their unconfined compressive strength in tons per square foot (tsf). - Type A soils have 1.5 tsf or greater - Type B soils range between 0.5-1.5 tsf, and - Type C soils have 0.5 tsf or less Lastly, stable rock is a natural solid mineral that can remain intact even when excavated using vertical sides. The competent person must use at least one manual and one visual analysis as per OSHA standards or permitted by the ASTM. Organisations can opt to skip this step by designing their protective systems for the least stable type of soil, which in this case is type C. No matter which type of protective system is used, the trench must have a means of outlet, like a ramp, ladder, or stairs. The four types of protective systems 1. Sloping This involves removing the soil and sloping the trench wall at an inclined angle away from the excavation, with an increasingly flatter angle providing better protection. The angle required by OSHA standards depends on the type of soil and its water content, but other variables, such as the soil type or an engineer’s design, can also help calculate the ideal slope to use. 2. Shoring Shoring entails installing some type of support, such as aluminium hydraulics, to keep the faces of an excavation from caving in. Shoring systems are often required to support adjacent structures, such as walls, buildings, and pavements. Project leaders must provide such support to ensure the stability of adjacent structures and the protection of their workers. Developing excavations that undermine pavements, sidewalks, and appurtenant structures is prohibited unless a properly designed support system or any other proven method is established to protect workers from a potential collapse of the structures. 3. Shielding This protective system safeguards workers in the event of a cave-in by keeping debris from falling on them. Trench shields, trench boxes, and other supports are typically constructed with sidewalls held apart by interchangeable aluminium or steel spreaders to accurately match the width of the trench. 4. Benching Benching is essentially the same as sloping in that it involves removing material from the face of an excavation, with its sides dug up to form horizontal steps or levels. A simple benching would have the sides sloped downwards with one step cut in at the bottom, while multiple benching calls for cutting a sequence of steps into the sides of the excavation. It is important to note that type C soil is not conducive for installing benching systems. Conclusion When considering measures to implement for construction site safety, prioritising trench safety by installing protective systems is paramount to steer clear of preventable accidents. While these systems are usually only required for excavations deeper than 5 ft, it is considered best practice to stabilise all trenches, big or small. More importantly, protective systems on the work site need daily inspection and maintenance to ensure they remain in good working condition. To keep your workforce updated on the best practices regarding trench safety and other aspects of workplace safety, consider signing them up for additional training here at Wong Fong Academy. From safe lifting operations to occupational first aid training in Singapore, we offer quality training and certification courses vetted by regulatory bodies, ensuring you get the most relevant information possible.
