1. The Case of the Disturbed Soil
P O W E R P O I N T ® T R A I N I N G
Target Audience: This session is most appropriate for construction workers and supervisors who work in and around trenches. This session is probably not appropriate for workers who are not expected to work in or around trenches.
Learning Objectives: This case and its training message primarily have to do with recognizing signs of potential trench collapse. It can be used as part of a complete trench safety training session, or it can be used as refresher training.
Background for the Trainer:
This training session presents a case study of an actual accident inspected and documented by the Occupational Safety and Health Administration (OSHA). The case presented in this training session is:
Accident: : One Employee Killed and Three Injured in Trench Cave-in
Report ID:
Inspection:
You may choose to present this training information in a lecture format, or make the training presentation interactive by engaging your class in discussions that will help them identify facts of the case, potential causes of the accident, and future accident prevention measures. In either case, students will benefit by learning from a real-life scenario.
Before beginning your training session, print and make copies of the one-page Case Study Student Handout, which is provided on the disc. The Case Study Student Handout can be used as a worksheet during the training session, or as a take-away reminder once the training session is complete.
Also, print and make copies of the Case Study Quiz, which is provided on the disc as a fully customizable Word document. The students can take the quiz at the end of the training session in order to help reinforce the information presented. Note that the same quiz is included at the end of this PowerPoint presentation as actual slides to review in class.
Consider taking pictures of your employees as they work in trenches. You can add these pictures to the presentation by inserting them into existing slides or creating new slides.
Make sure the trainees understand the message as you go along. Ask questions periodically to test their understanding.
Speaker’s Notes:
Welcome everyone. Today we will conduct a case study of an actual accident investigated by the Occupational Safety and Health Administration (OSHA). This is an actual tragic workplace accident that had real-life implications for the worker, the worker’s family, co-workers, and the employer. The Case Study may be disturbing and may even involve a fatality.
The purpose of this training session is to teach and reinforce the importance of working safely in trenches in order to prevent tragic accidents. In particular, it deals with how to identify conditions that could lead to a trench collapse. The intention is to learn from the accident and take steps to prevent a similar accident from changing our lives.
Trench Collapse—
The Case of the Disturbed Soil
©2003

2. Let’s Look at the Stats
About 400 U.S. workers die in trench-related accidents each year
About 6,400 U.S. workers are seriously injured each year
Soil weighs 125 lb per cubic foot
Soil from a trench cave-in puts approx. 800 lb of force on the chest of a trapped worker
Speaker’s Notes:
According to OSHA, about 400 U.S. workers die in trench-related accidents each year.
About 6,400 U.S. workers are seriously injured each year in trench-related accidents.
Soil weighs about 125 pounds per cubic foot. When wet, soil can weigh as much as 145 pounds per cubic foot. The soil will crush a worker to death in a cave-in.
A worker can suffocate even when his nose and mouth are not buried by soil. If a worker is buried up to his neck, he will probably suffocate because he will not be able to expand his chest to take a breath. The soil puts over 800 pounds of force on a worker’s chest, making it almost impossible to expand and get sufficient breath.

3. Take a Look at the Facts 4 employees working in a trench
Employee #1 at the south end measuring
Employees #2, #3 standing on pipe
Background for the Trainer:
Training Option: Pass out the Case Study Student Handout. You may have the students read the accident description to themselves before discussing it in the class, or you may use the bullet points on the slide and the speaker’s notes below to describe the accident.
Speaker’s Notes:
Four employees are located in a trench measuring about 79 feet long. They are installing sections of sanitary sewer pipe. Employee #1 is located at the far south end of the trench holding a measuring rod to check the slope at the end of the section of pipe they were installing. Employees #2 and #3 are attempting to level the section of pipe by standing on it. Employee #4 is just south of Employees #2 and #3.

4. Take a Look at the Facts (cont.)
No trench protection
Walls of trench collapse
1 employee killed and 3 injured
Speaker’s Notes:
The trench is 10 feet deep. The top of the trench is 7 feet wide and the bottom of the trench is 6 feet wide.
There is no trench protection.
The sides of the trench do not have adequate sloping to prevent a cave-in.
One employee is killed and three employees are injured when the trench collapses.

5. Take a Look at the Facts (cont.)
Previously disturbed soil, Type C
Water in the bottom of the trench
Numerous soil cave-ins previously
Nearby heavy equipment and vehicular traffic
Speaker’s Notes:
The trench excavation site was composed of previously disturbed, cohesionless, granular soil, which is classified by OSHA as a Type C soil.
Water was present at the bottom of the trench.
Numerous small soil cave-ins had occurred previously.
Heavy equipment and vehicular traffic was operating adjacent to the trench. In fact, the trackhoe was operating near Employee #1 when the trench collapsed.

6. What Do You Think Went Wrong?
What type of trench protection could have been used?
How much side slope is required for trenches dug in Type C soil?
What are some signs of potential trench collapse?
What can contribute to soil instability?
Background for the Trainer:
Use the questions on this slide to elicit discussion.
Training options: After reviewing this slide and the accident description, give the class 5-10 minutes to discuss the accident description in small groups; or ask the students to try to determine some of the facts, potential causes, and possible prevention measures. In either case, use the Case Study Student Handout as a way to encourage discussion as you go through this presentation.
Speaker’s Notes:
Let’s take a few minutes and, using the Case Study Student Handout, work in groups to try to determine the facts of the accident, potential causes of the accident, and possible prevention measures. Then we will review the Case Study together in class.
Consider some of the questions on this slide when discussing the Case Study in your groups.

7. Let’s Review the Causes
No trench protection system
Inadequate slope of trench sides
Vibration from nearby heavy equipment
Water in the trench
Trench inspections not conducted regularly
No person on safety watch
Background for the Trainer:
Try to get the trainees to put themselves in the place of the person in the case study. What would they have done in this case?
Point out how a near miss can turn into a catastrophe in the presence of emergencies. In this case, workers ignored the near misses of a number of previous small soil cave-ins. The workers probably wanted to just get the job done quickly and not have to worry about dealing with protection systems such as side sloping or trench boxes.
Speaker’s Notes:
No trench protection system was provided. The walls of this trench should have been stabilized with engineered shoring, or workers should have been protected with adequate shielding, such as portable trench boxes, which are commonly used in piping installations.
Without trench protection, the walls of the trench should have been sloped. Type C soil is unstable and requires a slope of 1½ feet horizontally for 1 foot of vertical. This trench was sloped 1 foot horizontal for 10 feet of vertical. It should have been sloped 15 feet horizontal for the 10 feet of vertical.
Vibration from the nearby trackhoe, as well as the weight of the trackhoe operating near the trench, could have contributed to the soil distress and the eventual cave-in.
Water in the trench is a sure sign of saturated soil, which is very unstable. The report of the accident indicates that numerous smaller cave-ins had occurred due to the water seeping in from the sides of the trench. This should have been another sign that the trench was not safe to work in.
Trench inspections were obviously not conducted by a competent person. Or, the inspections were ignored in a rush to get the job done. A trained and competent trench inspector would have evacuated all workers and not allowed the work to continue until protection systems such as trench boxes or wall sloping were installed.
No person was assigned the duty of safety watch. This person stands on top of the excavation and watches for any signs of cave-in. This worker would have noticed the numerous small cave-ins and evacuated workers until the proper protection systems were installed.
Can you think of any other causes that may have contributed to this accident?

8. Signs of Soil Distress Fissures or cracks Slumping of material
Bulging at the bottom of the excavation wall
Pebbles trickling into the excavation
Sinking of excavation’s edge
Speaker’s Notes:
Soil distress is a condition in which a cave-in is likely to occur. It is important for everyone who works in and around trenches to be able to recognize signs of soil distress in order to prevent accidents. When soil distress is recognized, action can be taken such as evacuating the trench, increasing the slope of the trench walls, shoring the trench walls, or installing shielding such as trench boxes.
Signs of soil distress include:
Fissures or cracks on the walls of the excavation.
Soil or rock slumping or falling from the walls of the excavation into the trench.
Bulging material at the bottom of the excavation wall could mean the soil is about to come into the trench.
Small pebbles or clumps of dirt trickling or rolling down the excavation wall.
The edge of the trench begins to sink down.

9. Conditions Causing Soil Distress
Nearby vibrating machinery
Nearby heavy, moving loads
Seeping water or rain
Hot, dry weather
Background for the Trainer:
Bring any written procedures your company has for excavating trenches—specifically for keeping vibrating machinery and heavy, moving loads away from excavations.
Bring any written procedures or checklists your company uses for inspecting excavations—specifically after a rainstorm or in hot and dry conditions.
Speaker’s Notes:
Certain conditions are known to cause soil distress, which could lead to a cave-in. Take steps to prevent these conditions to maintain the stability of the soil in which you are excavating. If you cannot take steps to prevent the condition (as is often the case with conditions caused by weather), do not proceed with work in the area until the soil has been stabilized.
Nearby vibrating machinery will vibrate the soil and cause it to settle down and inward toward the trench. Keep machinery away from trenches when possible.
Nearby moving heavy loads such as street traffic will compress the nearby soil downward, which in turn will push soil inward toward the trench. Keep vehicles away from trenches when possible.
Seeping water or rain can saturate the soil and reduce its cohesion, which means it is more likely to slump or slide into the trench. Saturated soil is much less stable than soil that is just damp.
Hot and dry weather can also reduce the stability of the soil. In hot and dry weather, the water in the soil will evaporate, and soil with no water content becomes unstable.

10. Don’t Let It Happen to You
Cave-ins occur suddenly
Soils have varying stability
Slope the trench walls appropriately
Use protection systems
Be aware of the signs of soil distress
Inspect excavations regularly
Background for the Trainer:
Show pictures of your company excavating safely with the use of sloped walls or protection systems.
Speaker’s Notes:
Let’s take a look at what we can do to prevent a similar incident from happening at our worksite.
Remember, cave-ins occur suddenly and, without warning. It is important to take any signs of soil distress seriously and use the appropriate protection system for the type of soil you are working in.
Soils are classified according to their stability. The soil type must be determined by a trained and competent person. Type A soils are the most stable and are primarily made of clay. Type B soils are less stable and are made up of silt, sandy loam, and medium clay. Type C soils, the least stable, are made up of gravel, loamy sand, and soft clay.
The type of soil determines the amount of slope. Type A soils should be sloped three-fourths of a foot horizontally for every 1 foot vertical. Type B soils should be sloped 1 foot horizontal for every 1 foot vertical. Type C soils should be sloped 1½ feet horizontal for every 1 foot vertical.
If sloping is not possible or practical, then use protection systems such as shoring or shielding. Shoring is a system, usually designed by an engineer, used to support the walls, and are designed to prevent a cave-in. Shoring is typically used in long-term excavations such as when constructing foundations for large buildings. Shielding does not prevent a cave-in; it protects the workers from a cave-in. Shields are designed to withstand the forces of a cave-in. Shields can be permanent or portable—such as trench boxes.
All workers should be aware of signs of soil distress and warn others when soil distress is detected. Also, post a worker above the excavation that is competent and knowledgeable in the hazards associated with trenching. This person watches the excavation walls for signs of a cave-in and has the authority to stop the excavation and order an immediate evacuation.
Inspections are conducted by a competent person each day before the shift starts, during the shift, after rainstorms, or after any other occurrence that may impact the stability of the excavation.
Are there any questions?
Thanks for your attention.

11. Quiz 1. Describe when excavations need to be inspected.
2. Describe why a worker buried up to the neck would not be able to breathe.
3. Describe two signs of soil distress.
4. What is the slope ratio for Type C soil?
5. Name two conditions that contribute to soil distress.
Background for the Trainer:
Remind employees that the quiz is to encourage further discussion and to help you, the trainer, be sure that everyone understands what was discussed.
Print copies of the quiz for participants to take on their own, or go over the questions as part of the training session.

12. Quiz (cont.)
6. Soil Type A is unstable and consists of silt, sandy loam, and medium clay. True or False
7. Soil type must be determined by a trained and competent person. True or False
8. Name a common form of portable protection used to protect workers from cave-ins.

13. Quiz Answers 1. Q. Describe when excavations need to be inspected.
A. Inspect trenches daily before each shift, during the shift, and when conditions change.
2. Q. Describe why a worker buried up to the neck would not be able to breathe.
A. The soil exerts about 800 lb of pressure, which prevents the chest from expanding.

14. Quiz Answers (cont.) 3. Q. Describe two signs of soil distress.
A. Cracks or fissures, slumping, bulging, sinking edge, trickling pebbles.
4. Q. What is the slope ratio for Type C soil?
A. 11/2 feet horizontal to 1 foot vertical.
5. Q. Name two conditions that contribute to soil distress.
A. Vibrating machinery, heavy moving loads, rain, hot and dry weather.

15. Quiz Answers (cont.)
6. Q. Soil Type A is unstable and consists of silt, sandy loam, and medium clay. True or False
A. False, Soil Type A is the most stable soil and consists primarily of clay.
7. Q. Soil type must be determined by a trained and competent person. True or False
A. True.

16. Quiz Answers (cont.)
8. Q. Name a common form of portable protection used to protect workers from cave-ins.
A. Trench boxes.