Module 13 Excavations

DISCLAIMER This material was produced under grant number SH-22248-1 from the Occupational Safety and Health Administration, U.S. Department of Labor. It does not necessarily reflect the views or policies of the U.S. Department of Labor, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government.

Objectives After this module you should be able to identify the most common excavation hazards take the steps necessary to avoid those hazards

Excavation Facts As many as 400 workers die and another 4000 injured as a result of cave-ins each year Most deaths occur in trenches 5-14 feet deep Cave-ins cause death by: suffocation, crushing, loss of circulation, falling objects 1 cubic foot of soil can weigh up to 140 lbs 1 cubic yard of soil can weigh up to 3000 lbs

Excavation Hazards Cave-in of a trench Contacting underground utilities Getting struck by falling objects Falling into an excavation Hazardous atmospheres Equipment rolling into excavations Also, conditions of the excavation change. They change from job to job, and they may change from day to day or even hour to hour.

Competent Person Every excavation job must have one This person must be trained on and knowledgeable in soils classification the use of protective systems the requirements of the OSHA standards This person must be able to identify hazards and immediately eliminate them Enter excavations only after their approval Competent person means one who is capable of identifying existing and predictable hazards in the surroundings, or working conditions which are unsanitary, hazardous, or dangerous to employees, and who has authorization to take prompt corrective measures to eliminate them.   Ensure that participants realize that this training alone does not qualify anyone to be a competent person. In regard to whether the competent person mentioned in 29 CFR 1926.651(k)(1) must be on site at all times, please be advised that there is no blanket requirement that a competent person be present at a construction jobsite at all times. The competent person can leave the site periodically, consistent with the goals of this section. It is the responsibility of the competent person to make those inspections necessary to identify situations that could result in hazardous conditions (e.g., possible cave-ins, indications of failure of protective systems, hazardous atmospheres, or other hazardous conditions), and then to insure that corrective measures are taken. It is, therefore, subject to the conditions present at each individual worksite whether or not a competent person is required to be present at the jobsite at all times.

this 6’ deep vertical-sided trench is dangerous because it is not protected This photograph shows an unprotected trench which workers had to enter to install pipe. Ask the class what they should do if the supervisor tells them to go in anyway. Corrective Actions: never enter a trench like this; notify your supervisor

What is a Cave-In? A cave-in is the separation of a mass of soil or rock material from the side of an excavation and its sudden movement into the excavation either by falling or sliding that could entrap, bury, or otherwise injure and immobilize a worker.

this worker is being exposed to a life threatening situation, an excavation with no cave-in protection This photograph shows a very serious hazard to the worker in the trench. Worker in excavation with no cave-in protection. [1926.652(a)(1)] Job-site conditions like this are extremely dangerous! Corrective Action: never enter a trench unless it is less than 5’ deep and you get permission from your supervisor or it has cave-in protection

Soil Types Excavation rules differ depending on the type of soil A competent person must determine the type of soil using at least one visual and one manual analysis Soil Type Description Stable Rock most stable Type A stable soil Type B disturbed soil Type C loose soil

Shielding Shield (shield system) means a structure that is able to withstand the forces imposed on it by a cave-in and thereby protect employees within the structure. Shields can be permanent structures or can be designed to be portable and moved along as work progresses. Shield systems must not be subjected to loads exceeding those that the system was designed to withstand. Shields must be installed in a manner to restrict lateral or other hazardous movement.

The Theory of Shielding Shielding does not actually prevent a cave-in Trench shields and boxes, if installed correctly, are designed to protect workers from the forces of a cave-in In order for the shield to do its job, the worker must stay within the protection of the shield even when entering and exiting

this trench is not shielded to the trench bottom properly; these workers are still at risk for a cave-in This photograph shows a trench box which was not installed properly. Remember, there must be no more than 2’ of unprotected side-wall below the box. Corrective Action: shield the trench to no more than 2’ from the bottom

the same shield is missing struts/crossbraces This photograph shows a trench box with missing components. Practices like this can greater reduce the boxes ability to protect the worker. Corrective Action: always install manufactured shielding according to the manufacturer’s directions

this incomplete installation provides little if any protection; in fact, the panels themselves can become a crushing hazard This photograph shows complete disregard for the proper set-up. Also, note that the excavation is located right next to regular traffic pattern. The vibration from the traffic can loosen the soil. Corrective Actions: always install manufactured cave-in protection according to the manufacture; never skip steps

these workers have left the protection of their trench box; a cave-in could happen at any moment This photograph shows workers who have left the protection of their trench box. Work should be planned so workers are never left without protection. Corrective Action: never work unprotected, cave-ins can happen anytime without warning

Shoring Shoring (shoring system) means a structure such as a metal hydraulic, mechanical or timber shoring system that supports the sides of an excavation and which is designed to prevent cave-ins.

The Theory of Shoring Shoring prevents cave-ins Shoring, if designed and installed correctly, counteracts the force of a cave-in In order for the shoring to do its job, the worker must stay within the protection of the shoring even when entering and exiting the trench

make-shift, improperly designed shoring does little other then provide a false sense of security This photograph shows one contractors attempt to prevent a cave-in. Ask the class if they think this type of shoring will work? Corrective Action: manufactured shoring should be used; install the shoring according to the manufacturer

This photograph shows the results of a cave-in This photograph shows the results of a cave-in. Note the make-shift wood shoring. A worker in this situation would have little chance of survival.

Sloping and Benching Sloping (sloping system) means a method of protecting employees from cave-ins by excavating to form sides of an excavation that are inclined away from the excavation so as to prevent cave-ins. The angle of incline required to prevent a cave-in varies with differences in such factors as the soil type, environmental conditions of exposure, and application of surcharge loads.

The Theory of Sloping and Benching Sloping and benching prevents cave-ins Sloping and benching, if done correctly, removes the risk of cave-ins by widening the trench from the bottom up

this worker is able to work without the fear of a cave-in

this pipeline trench is benched to prevent cave-ins

Ramps, Ladders, and Stairs Ingress and egress mean "entry" and "exit," respectively. In trenching and excavation operations, they refer to the provision of safe means for employees to enter or exit an excavation or trench. Ask the students why a worker would need to get out of a trench in a hurry.

the worker in this trench has no safe means of exit This photograph shows a worker with no means of getting out of the trench in a hurry. OSHA would cite the employer for no ladder in the excavation for access/egress. [1926.651(c)(2)] Corrective Action: for trenches 4’ deep or greater, install a ramp, ladder, or stairs no less than every 25’ from a worker in the trench

Additional Concerns Underground utilities Overhead hazards Mobile equipment Walkways Water in excavations Hazardous atmospheres

striking underground utilities can be deadly Your first step in excavation work is the use the one-call system to locate underground utilities. In most cases, the one-call number is 811. When finding the exact location of underground utilities, proceed with caution, by hand or other acceptable safe means. The use of heavy equipment for potholing is strictly prohibited! If digging with a hand held shovel, position the spade of the shovel so it’s parallel with the underground installation. Use only enough force to gently penetrate the ground while looking for signs of backfill, utility coverings, or other indicators of warning. this worker has used the one-call system to locate utilities; also, he is using safe and acceptable means to find the exact location of the utility

this worker is at risk of being struck by falling rocks and excavated materials, in particular this soil spoil is too close This photograph shows the spoil pile too close to the edge for worker safety. [1926.651(j)(2)] Corrective Action: keep excavated material (spoil) at least 2’ from the edge of the excavation

This photograph shows many overhead hazards other than the dirt that was taken out to create the hole. Corrective Action: keep tools materials and other project related items at least 2 feet from the edge

when mobile equipment is operated adjacent to an excavation, the operator must have a clear and direct view of the edge of the excavation, or… This photograph shows the potential result of not addressing mobile equipment hazards related to excavations. As a side note: Ask the students what they think would have happened to the operator if he had not been wearing his seat belt. … a warning system shall be utilized such as barricades, stop logs, or hand or mechanical signals; if possible, the grade should be away from the excavation

using this method to cross an excavation can result in a serious fall Class discussion: Ask the class if they have ever seen anything like this? Next ask them if they have ever had to cross a trench this way? Have the class come up with a conclusion of the worst possible scenario should they fall. Corrective Action: construct a proper and safe walkway

this is an example of a proper walkway This photograph shows a contractor’s solution to eliminate the fall hazards associated with his excavation. walkways or bridges must have a safety factor of 4, have a minimum clear width of 20”, be fitted with standard rails, and extend a minimum of 24” past the surface edge of the trench

the presence of water usually means soil that is unstable This photograph shows an excavation full of water. Once water is present, the soil must be classified as type “C” (the most unstable) and protection chosen accordingly. Water must also be removed and controlled.

excavations must be kept as water free as possible This photograph shows the actions needed to remove the water and maintain that removal. Employees shall not work in excavations in which there is accumulated water, or in excavations in which water is accumulating, unless adequate precautions have been taken to protect employees against the hazards posed by water accumulation. Corrective Actions: select, inspect, and use water removal equipment correctly; consider such things as air-quality and personal health issues

with the water pump running, a possible carbon monoxide exposure now exists Where oxygen deficiency (atmospheres containing less than 19.5% oxygen) or a hazardous atmosphere exists or could reasonably be expected to exist, such as in excavations in landfill areas or excavations in areas where hazardous substances are stored nearby, the atmospheres in the excavation shall be tested before employees enter excavations greater than 4’ in depth. Adequate precautions shall be taken to prevent employee exposure to atmospheres containing less than 19.5% oxygen and other hazardous atmospheres. excavations greater than 4 feet in depth must be evaluated for oxygen deficiency, flammability, and toxicity

these workers installed a high exhaust pipe to prevent asphyxiation When controls are used that are intended to reduce the level of atmospheric contaminants to acceptable levels, testing shall be conducted as often as necessary to ensure that the atmosphere remains safe.

compressed gas cylinders are not to be brought into trenches This photograph shows the proper and safe location for compressed gas cylinders when it comes to excavations.

trying to keep as many air contaminants as possible above grade is a good idea This photograph shows a worker applying a chemical to pipe before he enters the trench.

Applicable Standards 1926 Subpart P Excavations

Your Employer is Responsible For Preplanning the work Protecting you from cave-ins Inspecting the excavation at least daily and throughout the shift as needed Taking prompt corrective action when needed

Your Employer is Responsible For Making sure a ladder is within 25’ of your work area when deeper than 4’ Ensuring that excavated dirt, rocks, and other materials are kept back 2’ from the excavation’s edge Testing the air in areas suspect to atmospheric hazards

You are Responsible For Following you company’s excavation and trenching safety rules Never enter a vertical-sided trench unless it is less then 5’ deep and you get permission from your supervisor Never enter a trench unless it is laid back, shielded, boxed, or in solid rock If a trench box is used, never leave its protection while in the trench

Memory Check How many feet must the excavated soil, your tools, and other supplies be kept back from the excavation’s edge? 1 foot 2 feet 7.5 feet 25 feet The correct answer is b. 2 feet.

Memory Check At what depth must a ladder, ramp, steps or runway be present for quick worker exit? 4 feet 5 feet 10 feet it is never required The correct answer is a. 4 feet.

Memory Check What is the greatest hazard facing a worker while working in a trench? hazardous atmospheres falls cave-ins falling objects The correct answer is c. cave-ins.

Memory Check Unless a competent person indicates that there is a potential for a cave-in, at what depth is a protective system required for a trench? 2 feet 4 feet 5 feet 10 feet The correct answer is c. 5 feet.