All types of soil are capable of collapsing without warning. It is also possible that you will encounter multiple types of soil in a trench wall; this is considered a “layered soil,” and is the most dangerous to work in or around, due to its makeup.
The strength of the soil
Identifying the strength of the soil is critical. Rescue teams and engineers have tools and devices such as pentrometers that are used to measure compressive soil strength, but a simple field test a responder could use is referred to as a “Thumb Penetration Test.” In that test, a responder takes a sample from the top of the spoil pile, to represent the bottom of the trench, and a sample of the bottom of the spoil pile, to represent the top of the trench, and compresses the soil into a ball. The responder then presses a thumb into the sample to make an impression that stays.
Additionally, a plasticity test can be performed on the soil. A rescuer takes a sample of soil and tries to roll the sample into small, thin pencil-like strips of soil; any soil that is over the width of the palm can be considered to have positive cohesiveness. But remember why the department is there – the trench has already failed.
Setting up the scene
First-arriving units must set the tone for successful mitigation. If a trench rescue team has not been summoned on the initial alarm, it must be requested to respond immediately. Other on-scene operations should include the following:
• Size-up – Identify the cause of the collapse and how many victims are trapped. Consider what the entrapment is – soil or additional materials? Many times, pipes, vaults, machinery and other materials fall into the trench, which can result in added mechanisms of entrapment to the victims.
• Primary assessment – Determine who is in charge at the trench site (sometimes referred to as the “trench boss”) and keep that person at your side. The trench boss can be a source of information in relation to accountability of missing workers, language barriers, purpose for the trench, equipment needs and potential hazardous material presence.
• Victim locators – Identify clues about where a victim may be buried. While there may be a general area where a victim may be located, the position of the victim can vary based on the actions the victim was performing prior to the collapse. Look for clues: tool buckets, lunch boxes, pipe joint materials, flag stakes or engineer hubs (used to identify the location of a trench), laser targets and personal protective equipment such as hard hats, protective eyewear and work gloves.
• Secondary assessment – Consider who is responding and what special units may be needed on scene. These include vacuum trucks, hazmat teams, local utility providers and ambulances, and they should be requested early. This operation will be manpower-intensive; be sure to have plenty of responders in the tactical reserve to replace rescuers who are performing support functions (cutting stations and spoil pile removal, for example). Managing traffic and crowd control will be of importance. Be sure local law enforcement is notified of the need to re-route traffic within the affected area and to keep spectators from becoming additional victims. A good rule of thumb is to start the “hot zone” a minimum of 100 feet from the incident.
By the time these tasks are completed, the rescue teams and forward Incident Support Team (IST) personnel should be arriving. This does not relieve initial-alarm companies from the incident, because many tasks need additional personnel, such as laying ground pads, ventilation, atmospheric monitoring and other support functions that will need to be completed. All resources will be needed to keep the scene safe, efficient and successful.
Emergency personnel will be called to these incidents in their jurisdiction, regardless of whether they have the skills needed to perform victim removal. Since they will most likely be first on scene, it is vital that the steps taken by the initial companies ensure the highest probability for success. Having these tasks completed prior to the arrival of the rescue unit will allow the specialists to go right to work on victim removal, increasing the potential for success.