HAZWOPER 40 - Lesson 18: Excavations

Hazardous Atmospheres

For excavations greater than four feet in depth, wherein there is found potential for oxygen deficiency or other hazardous atmospheric conditions, or wherein any such conditions can reasonably be expected to exist, inspection by a competent person must take place before any employee is allowed to enter. If hazardous conditions are found to exist, proper equipment such as respiratory protection, ventilation, and masks must be provided. All such equipment is required to be tested on a regular basis to ensure its usefulness in time of need. In the event that an employee has to wear a lifeline in an excavation, an observer must be present to ensure that: The lifeline is working properly at all times. Communication with the employee is maintained.

Excavation Definition

According to OSHA construction safety and health standards, an excavation is any man-made cut, cavity, trench, or depression in the earth's surface by the removal of earth. This includes any excavation for construction or maintenance purposes as well. A trench is a narrow excavation made below ground level in which the depth is greater than the width. The maximum size of a trench is limited to a width of 15 feet.

Safety before Beginning the Job

Before beginning the job, a health and safety program for the site should be developed. Its purpose should be to educate all workers on the identification of potential work hazards. The program should also layout guidelines for emergency situations. It is important for every contractor to establish and maintain a safety and health program for the work site that outlines in detail the work and safety policies, procedures, and practices that will be followed to protect employees. This program should be used for safety education. To be effective, such a program should also include provisions that are site and job specific. The safety program can be communicated verbally or in writing. There must be complete cooperation between all workers at the site regardless of rank and position. Each supervisor must be clearly knowledgeable about his or her area of responsibility as well as his or her authority. Affected unions should also be notified of work plans and be asked to cooperate. The following principles should be strictly adhered to: Employees exposed to vehicular traffic must be provided with warning jackets and other equipment made of reflective/high-visibility material and their use should be ensured at all times. No employee shall operate a piece of machinery or equipment without first being trained to handle it and fully alerted to its potential hazards. The site safety and health program should require immediate notification and investigation of accidents.

Cave-ins

Cave-ins pose the greatest danger to all excavation workers. Recall that OSHA requires sloping, benching, supporting, or shielding the sides of the excavation. The design of a protective system depends on many factors including: Soil classification Depth of the cut Water content of the soil Weather conditions Nearby operations The Standard provides four approaches for sloping and shoring, including the use of shields. Any of these techniques can be used to provide the required level of protection against cave-ins.

Introduction

Cave-ins pose the greatest risk to all excavation workers. For this reason, managers and supervisors must set a standard for good safety practices by ensuring that all regulations are followed down to the smallest detail. Employees must be properly trained in the use of all safety gear and equipment, and the most practical shoring devices must be implemented per performance criteria determined by the Occupational Safety and Health Administration (OSHA).

Support Systems

Contractors can also use a shield or trench box designed by or according to parameters approved by a registered professional engineer. Any suitable material can be used, given that it provides at least the same level of protection as an appropriate shoring system. The employer/contractor is free to choose the most practical design depending upon his or her approach for any particular circumstance. It must, however, meet the performance criteria set by OSHA.

Learning Objectives At the completion of this lesson, you will be able to:

Explain the factors on which the design of a protective system depends. Name the four approaches provided for sloping and shoring. Identify the maximum allowable slope for any simple slope excavation. List the OSHA guidelines for protecting employees when installation of support systems is taking place. Describe the five precautions for averting falls or falling loads.

Falls and Equipment

In addition to cave-in and related hazards, other threats are exposure to falls or falling loads and mobile equipment.

Safety Planning

It is always advisable to plan ahead for safety at the work site. This helps to avoid any unforeseen situations. Detailed studies have shown that most on-the-job injuries are a direct result of inadequate initial planning. Although errors become much more obvious after work on a project has commenced, it will generally take longer to take corrective action. Before preparing a bid, the following site conditions need to be taken into account: Traffic flow in the region. Proximity to constructed structures and their condition. Soil texture at and around the work site. Surface and groundwater. Height of the water table. Location of all overhead and underground utility installations that might be affected by the work. Weather. To determine these and other job-specific conditions, consult with local officials and utility companies. Before any excavation actually begins, the Standard requires the contractor to determine the exact locations of all utilities and other installations that may be encountered during the digging process. It is essential for the contractor to contact and inform utility companies or owners of such installations before commencing work. The contractor must comply with established or customary response times for the proposed work. The contractor must also ask utility companies or installation owners to identify the exact locations of installations. Most states have a "One-Call" system. For example prior to starting a project, dial 811 on a telephone and schedule a locate. The utility locator will mark locations of buried lines with a paint color corresponding to each type of utility. Update these utility locates every 30 days. To locate a utility, use "Soft Dig" techniques to get a visual locate on a line before engaging with machinery. Soft dig can be a "pothole" dug with hand shovels (avoid pick axes to prevent penetrating a line). A hydro-excavator is also acceptable means as not to damage the line. Once a positive locate is made, a spotter should watch the bucket at all times. Best practice is to keep the excavator bucket at least 2 feet away from the line and to strip off the remaining soil by hand to avoid contact with the line if it turns or has a buried appurtenance like a valve sticking out. Not all utilities will show up in a mark-out and there is always a possibility of an unmarked utility strike. You never know what is buried beneath you, especially in old industrial sites, so always excavate with extreme caution and use a spotter when it is a safe atmosphere on the ground to do so. If the exact location of installations cannot be ascertained for any reason whatsoever, or if the utility does not respond within 24 hours, the contractor can proceed with the work using caution. In order to determine the exact location of underground installations, workers must use safe and acceptable measures. For instance, if underground installations are exposed, OSHA regulations require that they be removed, protected, or properly supported. Once all necessary data pertaining to the job site has been assembled, the contractor is in a position to determine the amount, kind, and cost of necessary safety equipment. An inventory of all equipment on hand should be compiled in order to determine additional needs. Regardless of the contractor's past safety record and experience, it is highly essential that each job be treated with the highest degree of care and preparation.

Safety Precautions

It is essential that the employer provide support systems such as shoring, bracing, or underpinning to ensure the stability of adjacent structures such as buildings, walls, sidewalks, or pavement. Excavation below the level of the base or footing of any foundation or retaining wall is strictly prohibited by the Standard unless one of the following conditions is met: A support system such as underpinning is provided. The excavation is in stable rock. A registered professional engineer determines that the structure is sufficiently distant from the excavation and that the excavation will not pose a hazard to employees.

Lesson Focus This lesson focuses on the following topics:

OSHA Guidelines Safety Planning Cave-ins Support Systems Other Hazards

Installation and Removal of Protective Systems

OSHA has set the following guidelines with respect to the protection of employees when installing support systems: Ensure that the members of the support systems are securely connected. Safely install support systems. Ensure that members of the support system are never overloaded. Install additional members to carry the load on the support system when temporary removal of individual members is necessary. The Standard also permits excavation of two feet or less below the bottom of the members of a support or shield system of a trench if: The system is designed to resist the forces calculated for the full depth of the trench. There are no indications, while the trench is open, of a possible cave-in below the bottom of the support system. The installation of all support systems is closely coordinated with the excavation of the trenches. The excavation must be back-filled as the protective system is dismantled after work is completed. After the excavation has been cleared, workers should slowly remove the protective system from the bottom up, taking appropriate care to slowly release the members.

Falls and Falling Loads

OSHA requires all employers to take the following precautions to avert this threat: 1. All material or equipment that could potentially fall or roll into an excavation must be placed at least two feet away from the edge of the excavation, have retaining devices, or both. 2. Alert all staff to the edge of an excavation by means of mobile equipment, barricades, hand or mechanical signals, or stop logs. 3. Scale the slopes to remove loose rock or soil or install protective barricades and other equivalent protection to prevent injury from falling rock, soil, or materials. 4. Prohibit employees from working on faces of sloped or benched excavations at levels above other employees, unless employees at lower levels are adequately protected from falling, rolling, or sliding materials and equipment. 5. Prohibit employees from going beneath lifted loads. To avoid being struck by any spillage or falling materials, require employees to stand away from vehicles being loaded or unloaded. If cabs of vehicles provide adequate protection from falling loads during loading and unloading operations, operators can remain in them.

On-the-Job Safety Evaluation

OSHA requires inspection of the excavation site and adjoining areas for possible cave-ins, failures of protective equipment and systems, hazardous atmospheres, and other hazardous conditions. On a daily basis, a competent person must perform these inspections. A full-time safety official should be appointed for larger and more complex operations. The safety official should make recommendations to improve the implementation of the safety plan. In smaller operations, however, either part-time safety officials are employed, or the supervisor assumes safety responsibilities. It is essential that supervisors conduct inspections, investigate accidents, and identify hazards. They are responsible for representing the contractor and protecting employees by ensuring that all undergo on-the-job safety and health training. Supervisors should constantly review all safety and health precautions to strengthen the safety plan's effectiveness. Supervisors should also ensure full cooperation by all employees in matters of health and safety and report all matters regularly to the contractor. Managers and supervisors should set safety examples by making sure that they follow all regulations to the smallest detail. Employers must also make sure that workers are properly trained in the use of all safety gear and equipment, and that they are using safe work practices.

Sloping and Shoring

One method is to slope the sides of the excavation at an angle of not more than 34 degrees measured from the horizontal. This can be easily achieved by sloping the sides to an angle not steeper than one-and-one-half horizontal to one vertical, as discussed previously. PDF: http://icourseplayer.360training.com/courses/assets/Haz40_mod18_sloping.pdf A second design method, which can be applied to both sloping and shoring, involves the use of tabulated data, such as tables or charts, approved by a registered professional engineer. All such data must be in writing and include sufficient explanatory information to enable the user to make a selection. It is also essential to include criteria for determining the selections and limitations on the use of data. A copy of the information, including the identity of the approving engineer should be maintained at the site at all times. After the work is completed, the information can be removed from the site and stored, but a copy must be made available, upon request, to Assistant Secretary of Labor for OSHA.

Work under loads handled by lifting or digging equipment should be ________.

Prohibited

OSHA Guidelines

The Occupational Safety and Health Administration (OSHA) has, since 1971, repeatedly made amendments and adjustments to its excavation and trenching related standards to increase safety for workers and reduce the severity and frequency of excavation accidents and injuries. The current Standard has been effective since March 5, 1990. However, it was amended in 1994. Trench/Trench excavation: Means a narrow excavation (in relation to its length) made below the surface of the ground. In general, the depth is greater than the width, but the width of a trench (measured at the bottom) is not greater than 15 feet (4.6 m). If forms or other structures are installed or constructed in an excavation so as to reduce the dimension measured from the forms or structure to the side of the excavation to 15 feet (4.6 m) or less (measured at the bottom of the excavation), the excavation is also considered to be a trench. For example, a wide excavation gets a concrete vault box installed inside of it. Now there is a narrow space between the wall of the excavation and the wall of the vault box. If the excavation wall gave way, workers could be pinned against the box. Additional sloping or shoring may be required. The Standard contains a method of soil classification, sloping and benching requirements, shoring and shielding device regulations, timber tables, hydraulic shoring tables, and a graphic summary of all Standard requirements. Types A, B, and C soil have different sloping and benching limitations. Digging beyond 20 feet deep requires additional protective system considerations. The primary hazard of trenching and excavation is employee injury from collapse. Soil analysis is important in order to determine appropriate sloping, benching, and shoring. Additional hazards include working with heavy machinery; manual handling of materials; working in proximity to traffic; electrical hazards from overhead and underground power-lines; and underground utilities, such as natural gas.

Trench Shields

The Standard exempts excavations from the use of a protective system when: The excavated surface is made entirely of rock. The excavation is less than five feet deep and a competent person has examined the ground and found no indication of a potential cave-in.

Water Accumulation

The Standard prohibits working in excavations where water has accumulated or is accumulating, unless adequate protection measures have been taken. If water removal equipment is used to control or prevent water from accumulating, the equipment and its operation must be monitored at all times by a competent person to ensure its proper usage. If water is present in an excavation the soil class must be downgraded. The entry of surface water into excavations shall also be prevented by means of diversion ditches, dikes, or other suitable means such as wells. A competent person must also inspect excavations subject to runoffs. An Erosion Control Plan for larger sites is typically required by the state which ensures that soil does not wash off of the site during a rain event. Silt fences and drainage features should be used to prevent runoff of sediment into a "Navigable Waterway of the United States" which includes ditches, streams, creeks, rivers, lakes, bays, wetlands, etc. Stormwater samples may need to be collected during rain events to ensure contamination isn't reaching these environmentally sensitive areas.

Materials and Equipment

The employer is responsible for ensuring that all safety and protective equipment is in working condition at all times. Defective or damaged materials and equipment can result in serious excavation hazards. It is essential to ensure the following: That all materials and equipment are free from damage and defects. Manufactured materials are used in a manner consistent with the manufacturers' recommendations and in a way to prevent the employee's exposure to danger. A competent person must examine all materials and equipment to determine if they are suited for continued use. If not, they should be removed from service until repaired and approval is received for use by a registered professional engineer.

Other Hazards

There are many more threats and hazards to staff at a worksite, many of which have been highlighted, but the possibility of site and location specific hazards cannot be ruled out.

Lesson Description

This lesson, Excavations, discusses OSHA's guidelines for excavation work including factors to consider before preparing excavation bids such as area traffic flow, nearby activity, surface and groundwater, height of water table, weather, and nearby utility installations. All of these greatly affect the potential for excavation-related injuries like cave-ins. Cave-ins pose the greatest danger to all excavation workers. Therefore, OSHA requires that workers susceptible to cave-ins be protected from this possibility by sloping, benching, supporting, or shielding the sides of excavations. Considerations for which support systems to use on-site, and how to design them, make up a substantial portion of this course. Finally, other hazards like falls and falling loads are identified and ways to protect workers are discussed.

Hazard:

Trench collapses cause dozens of fatalities and hundreds of injuries each year. (Trenching deaths rose in 2003.) Solutions: Never enter an unprotected trench. Always use a protective system for trenches five feet deep or greater. Employ a registered professional engineer to design a protective system for trenches 20 feet deep or greater.

Protective Systems:

Use sloping to protect workers by cutting back the trench wall at an angle inclined away from the excavation not steeper than a height/depth ratio of 1.5:1, according to the sloping requirements for the type of soil. Use shoring to protect workers by installing supports to prevent soil movement for trenches that do not exceed 20 feet in depth. Use shielding to protect workers by using trench boxes or other types of supports to prevent soil cave-ins. Always provide a way to exit a trench (such as a ladder, stairway or ramp) no more than 25 feet of lateral travel for employees in the trench. Keep spoils at least two feet back from the edge of a trench. Make sure that trenches are inspected by a competent person prior to entry and after any hazard-increasing event such as a rainstorm, vibrations, or excessive surcharge loads.