Last month, we discussed the initial response, hazard recognition and mitigation points for the scene of a trench collapse. This month, we are continuing our discussion in the arenas of response size-up, various types of shoring and their applications and additional support operations that may be necessary on-scene. It should be noted that the trench rescue scene is a dynamic arena; things can change at a moment's notice. However, with proper training and procedures on-scene, we can bring the incident to a safe and successful conclusion.
An operational guideline should be in place, so that the response to a trench collapse includes the right equipment and personnel to operate. With many departments operating with a minimal manpower pool, it is imperative that the guideline includes automatic aid departments that are proficient in this area; as I have said before, manpower is the most precious resource that departments bring to any emergency scene.
Along with adequate manpower, there should be considerations for the following equipment as well:
These include the materials that will be put in place to make the trench safe. The sheeting materials can consist of Shorform, Finform or Euroform wooden panels. These panels are a minimum of one-inch high grade plywood that are coated with a phenolic resin that seals and strengthens the sheets to take the abuse of trench work without failing and cracking. These panels are fitted with uprights, which are 2-by-12 wood planks that provide considerable strength to sheeting, and also serves as an area for cross-bracing to be attached to. Many times, cross-bracing can include cut dimensional timbers, which will vary in size and diameter, depending on the size and soil type of the trench. These timbers are usually made from Douglas Fir or Southern Pine, as both will provide ample warning (cracking) prior to failure (see Photo 1). Wood shoring materials should be inspected for physical damage from flexing during operations, rot and decay, warping or any other defects that might cause the material to fail under pressure.
Other forms of cross-bracing include hydraulic struts, pneumatic struts, and screw jacks. Aluminum hydraulic struts are pre-engineered shoring systems that combine cylinders and either horizontal or vertical rails to support the sidewalls of a trench (Photo 2). Aluminum pneumatic struts are pre-engineered shoring struts made of aluminum cylinders that are charged with air to extend against the trench walls, set at a specific air pressure to meet the requirements of the soil type (Photo 3). These struts are then manually locked into place for maximum compressive strength. No matter the type of equipment, it is vital that all personnel are well-versed on their use and operation.
Tools and Appliances
There are other support tools and equipment that should be readily accessible at the scene, including:
- Pneumatic framing nailers and associated equipment
- Chop saws, circular saws, and chain saws
- Tape measures, pencils, chalk lines, speed squares, and claw hammers
- Pinch bars, sledgehammers, vent fans, and atmospheric monitors
- Camp shovels, five-gallon pails, utility rope, and patient packaging equipment
The size-up for the trench collapse should begin during the response to the scene. Familiarization with your jurisdiction should help you identify any target hazards that the area may possess and what resources you will need to abate them. Once on-scene, the primary focus should to regain some sort of control of the incident; it may be necessary to remove would-be rescuers from a dangerous area prior to your rescue operations. Furthermore, crowd control is essential; it will be necessary to keep onlookers, media personnel, and non-essential personnel away from the hot zone.