The Mine Safety and Health Administration (MSHA) has issued a serious accident alert and issued best practice guidelines on trenches.
The alert says that on June 29, 2017 two miners were attempting to access a plugged grizzly screen by excavating a slot cut trench when the trench walls collapsed, engulfing the miners.
During an initial rescue attempt, the walls collapsed further, trapping two additional miners. The material was waist high on three of the miners and was over the shoulders on the fourth miner. After several intense hours of rescue efforts, all four were freed from the debris and flown to a nearby hospital.
MSHA has issued a list of best practices:
• Ensure trench walls are either supported for the full height or sloped to a safe angle in any trench equal to or greater than 5 feet in depth
• Provide an egress method such as ramps, ladders or other safe way for workers to exit any excavation that is 4 feet or more in depth
• Rely on a professional engineer to design deep trench excavations
• Carefully examine ground conditions prior to performing tasks near excavated embankments, trenches, or ditches
• Keep excavated soil (spoils) and other materials at least 2 feet from trench edges.
• Identify hazards associated with the task to be performed and review those hazards with all personnel involved before beginning work
• Maintain awareness of changes in conditions that might affect trench stability.