Shorform panels are put in place and secured with wood cross-bracing at a trench collapse scene.
Photo 2: A set of pneumatic struts set in place during a trench operation.
Photo 4: Ground pads are laid in place around the perimeter of the trench. They help distribute the surcharge load of the rescuers and equipment operating around the trench.
Photo 5: Atmospheric monitoring and ventilation help make the trench safe to operate in. Both should be done immediately after the ground pads are in place.
Photo 7: This side wall shear occurred during a training class. The size of the shear was estimated to be approximately 8,000 pounds.
Photo 8: This lip-in took the lip of the trench wall in with it and anything that may have been in its way. Note the different layering of soil on the belly of the trench wall.
Photo 9: Fire service ground ladders are used for access into and out of the trench. Here, the ladders are secured to a pair of 2-by-12 boards, nailed and cleated into the ground pads.
Photo 10: Walers are installed to support the wall panels and allow for supplemental shoring to be installed for additional support.
Photo 3: A set of pneumatic struts set in place during a trench operation.
Photo credit: Photo by Michael P. Daley
Photo 6: This spoil pile slide resulted in an extra three feet of soil on the floor of the trench.
Photo credit: Photo by Michael P. Daley
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.
During this time, performing accountability of the staff on scene prior to the collapse is paramount; after that, it can be determined how many personnel are unaccounted for. These are some reasons why it is important to set up work zones on the scene. The "Hot Zone" is the area where the actual trench rescue operations are performed. This area can be up to five times the depth of the trench (see Photo 6). Next comes the "Warm Zone", which is the area where the command post, tool staging, shoring preparation, and other activities associated with the rescue are taking place. The last area is the "cold zone," located around the warm zone, for support operations. This remote area helps to ease load forces on the open trench, and is usually at least 20 times the depth of the trench away from the hot zone.
Many rescue teams have found it beneficial to carry a tactical worksheet or site survey sheet for trench rescue. The sheet is similar to a confined space permit; however, it is geared directly towards the hazards faced in a trench operation. Items such as trench dimensions, number of victims, utility hazards, and atmospheric monitoring results could be documented, along with on-site action checklists can be detailed specifically to these types of incidents.
Initial concerns also include the dimensions of the trench (both initial dimensions, and those after the collapse), any entrapment issues inside the trench besides soil, any utility hazards that are present inside the collapsed area, and the actual foreman at the scene; this person can provide vital information about what was going on just prior to the collapse, solve any language barriers that may exist, and identify any resources that they may be able to provide for you, such as wood, trench boxes, or heavy equipment.
Next, it is vital to determine what is currently going on at the incident. Any hazards that continue to cause danger on scene, such as vibrations, traffic congestion, energized utilities, and secondary collapse issues must be taken care of. A rapid intervention crew should be standing by, in the event of a secondary collapse that would entrap would-be rescuers.
The area of collapse may provide some clues as to the location of the missing worker. Items such as hard hats, tool belts, pipe strings and grease cans can give the rescuers an area of close proximity as to where the victim may be buried. This would provide an area for rescue operations to begin. It is important to consider that, although the victim may not be seen, that does not automatically make the incident a body recovery. It may be possible that the victim may be positioned in a manner that will protect the chest and allow for expansion from the weight of the collapsed materials. There may also be a situation where debris or equipment may have resulted in a void that allows the victim to breathe for some time while buried.
Once the initial size-up is completed, the rescuers can begin to make the trench area safe. Approaching the trench end, crews start to drop ground pads, which are used to help distribute the weight of personnel and equipment around the lip of the trench. These pads are 4-by-8-foot sheets of 3/4-inch plywood, with the exception of the spoil pile side. It may only be possible to lay 2-by-12 planks between the trench lip and the spoil pile. These ground pads are used to surround the trench area at least equal to the depth of the trench, and should overlap one another to assure there are no open areas of soil (see Photo 4). As crew members move the spoil pile further away from the lip, it may be possible to lay additional ground pads on that side of the trench.
While the ground pads are being placed, atmospheric monitoring and supplemental ventilation should be underway. It may be possible to collect methane inside the trench, which needs to be removed. Methane is a common gas found in the ground, and has a flammable range of 5.3 to 19.3 percent: it needs to be removed before a flash fire can occur and injure the victim and rescuers. Fans that are used for ventilation should be intrinsically safe, and be capable of moving a minimum of 1000 cubic feet of air per minute (see Photo 5).
It is vital that rescuers identify the type of collapse that has occurred. Some common types of collapses include:
- Spoil Pile Slide: This collapse occurs when the spoil pile slides back into the trench. Sometimes machine operators can mistakenly knock part of the spoil pile back into the trench, or the spoil pile may be placed too close to the lip, causing a surcharge load on the edge (see Photo 6).
- Side Wall Shear: This collapse occurs when a portion of the wall breaks off, and falls into the trench. Signs of impending wall failure include fissure cracks along the edge of the trench, and are more common in trenches that are open for long periods of time (see Photo 7).
- Slough-in: When there is poor water drainage in the trench soil, the belly of the trench wall falls inward, and creates a dangerous overhang under the ground pads. This is a tough trench to shore, as the voids created by the collapse need to be addressed.
- Lip-in: There are times when the weight of the spoil pile too close to the lip, or heavy machinery operating in the close vicinity of the trench can cause the lip to fail, taking everything on the lip (equipment, personnel, etc.) with it into the trench (Photo 8).
Once the collapse pattern is identified, crews can begin to shore up the walls of the trench. A means of egress, such as a ladder or stairway, has to be located no further than 25 feet of lateral distance for rescuers; this is best served as keeping the "two ways out" rule in mind (see Photo 9). Place at least two ladders for egress in the trench, one at each end. Sheeting panel assemblies are then laid into place, facing opposite of each other. Once in place, rescuers measure between the panels to install adequate cross-bracing. Cross-bracing will vary, with soil type, trench dimension, and type of bracing that will be employed. The bracing is then cleated and secured into place, and the process is repeated until there is a safe area to operate in to remove the victims.
The next step after the cross-bracing will include Walers, which are large-diameter wood dimensional timbers that will serve to support the initial panels and allow the installation of supplemental shoring timbers (see Photo 10). These Walers can be as big as 6-by-8-inch dimensional timber, based upon the size of the trench. The sheer size and weight of the Waler will require a lot of manpower to install, which may not be possible, due to the amount of room at the floor of the trench. Once the Waler system is installed, and supplemental shoring is in place, rescuers may remove the center cross-bracing, should there be a need for more room to allow for victim removal.
Along with shoring the trench, there are a lot of other things going on inside the trench. Patient care will be an on-going operation, in order to stabilize the victim while the soil is removed around them. With the potential for Compression Syndrome, it is vital that advanced life support (ALS) is on scene and providing necessary treatment. However, personnel inside the trench are limited to only one rescuer per shored sets of panels. For example, if there are only two sets of panels shored and in place, that will allow only one ALS provider and one rescue tech inside the trench for removal. Crews that are operating outside the trench can begin to prepare immobilization and removal equipment, so the victim can be packaged and removed as quickly and efficiently as possible.
Even though the victim has been removed and is receiving definitive medical attention, the scene is far from stabilized. Shoring equipment and tools that were used to make the trench safe will have to be removed. The process is reversed for removal, but the scene becomes more hazardous, as the trench has been open to the elements for a longer period of time, which may have allowed for the soil to become drier and more likely to collapse. Great care must be taken during demobilization so that all rescuers remain safe during the termination of the incident.
The scene of a trench collapse is a dynamic, high-risk environment that can result in injury and death to workers and rescuers alike. A trench can collapse at anytime without any audible or visible warning, especially when there is no protective systems put in place inside the trench. Some victims are would-be rescuers who were unaware of the hazards associated with these incidents; therefore, it is imperative that rescue from these situations should only be attempted by emergency personnel trained in trench rescue. It is imperative that responders that have this responsibility in their jurisdictions be adequately prepared for these operations.
Until next time, stay focused and stay safe.
MICHAEL P. DALEY is a lieutenant and training officer with the Monroe Township, NJ, Fire District No. 3, and is an instructor with the Middlesex County Fire Academy, where he is responsible for rescue training curriculum development. Mike has an extensive background in fire service operations and holds degrees in business management and public safety administration. Mike serves as a rescue officer with the New Jersey Urban Search and Rescue Task Force 1 and is a managing member for Fire Service Performance Concepts, a consultant group that provides assistance and support to fire departments with their training programs and course development. Mike was a panelist on Radio@Firehouse on the Successful Rescue Operations in Today's Fire Service podcast. You can reach Michael by e-mail at: FSEducator@aol.com.