Excavation work

The U.S. excavation work industry includes more than 18,000 establishments employing more than 116,000 workers according to the latest figures published by the U.S. Department of Commerce. Larger establishments (defined as those with 20 or more employees), account for less than 10 percent of the total number of establishments while taking in roughly 25 percent of all business done by this industry.

The two dominant costs of doing business in the excavation work industry are materials components and supplies, as well as payroll. Other costs include electricity; rental cost for machinery, equipment, and buildings; and cost of repairs to machinery and equipment.

The status of the U.S. excavation industry generally mirrors the country's economic climate, in particular the demand for construction of detached single-family homes. Typically single-family homes accounted for more than one-third of the value of all excavation work in the United States, while other commercial buildings represent less than one-fifth and educational buildings less than one-tenth.

The U.S. excavation work industry benefited from the sustained demand for single-and multi-family housing in the early 2000s. The recession of the early 1990s dropped housing starts to just 1.01 million in 1991, but the economic recovery that began in 1992 helped housing starts rise each year to a peak of 1.46 million in 1994. While starts dropped back to 1.35 million in 1995, they rose again to 1.45 million in 1996. In 1998 housing starts matched the 1996 number of 1.45 million, down slightly from the previous year. By 2002, however, housing starts had reached 1.70 million, 1.36 million of which were single-family, and 346,900 of which were multifamily. The National Association of Home Builders expects continued growth through at least 2005.

Because residential construction trends were up throughout the United States in the early 2000s, excavation work in these areas was booming despite a sluggish economy. Not surprisingly, most growth occurred in southern and southwestern states, which have experienced the strongest population growth in the United States during the 1990s and early 2000s. Among the top 50 markets, many of which experienced annual growth of 20 percent or better, were Dallas, Texas; Houston, Texas; Phoenix, Arizona; Atlanta, Georgia; and Las Vegas, Nevada. Florida leads the way in growth, attracting aging baby boomers who are looking for retirement homes or communities in warmer climates.

Small, independent operators remain the backbone of the excavation work industry. They generally work as subcontractors to home building companies, commercial construction firms, and others. Still, several large companies hold dominant market positions in this industry, though they tend to be regional and not national in scope. In 2003 the top companies in the excavation work industry included Freesen Inc., Springfield, Illinois ($130 million);

Excavation in construction is any operation in which earth, rock, or other material in or on the ground is moved or otherwise displaced by means of tools, equipment, or explosives, and includes earthwork, trenching, wall shafts, tunnelling and underground work. High-risk obligations apply to excavations with a depth greater than 1.5 metres.

The regulations covering construction work are contained in Part 12 of the Occupational Health and Safety (Safety Standards) Regulations 1994.

Hazards associated with excavation work

Without careful planing and management, an excavation site can be hazardous to all persons in the vicinity of the construction work. Particular hazards identified in relation to excavation work include:

• the depth of the excavation
• nature of the strata (soil variations creating the potential for the sides to collapse);
• fractures or faults
• the presence of water (from other sources)
• exposure to wet weather
  
• any load close to the edge of the zoned of influence
• the exposure time
• any previous disturbance
• adjoining buildings
• adjacent excavations
• vibration which may increase the potential to collapse
• the presence of existing underground services
• chemical gases

For other hazards which may affect excavation work see Construction fact sheet

Risks associated with excavation work 

Excavation work is inherently dangerous and regarded as the most dangerous construction work. Excavation failures occur quickly and this limits the ability of the worker to escape especially if the collapse is extensive or is a trench.

The speed of an excavation collapse increases the risk associated with this type of work and the consequences are significant as the falling earth can bury or crush any person in its path. This can result in death by suffocation or internal crush injuries.

The magnitude of the consequences particularly in relation to trench collapse highlights the need to protect the employees and other person working at or near excavations sites.

Employer’ duties

Under the Occupational Health and Safety Act 1991 (the Act) employers are required to provide and maintain, as far as is practicable, a working environment that is safe and without risks to health.

To ensure that the risks are managed in accordance with the duties outlined under the Act employers should systematically manage the risks to health and safety which arise from excavation work

Employers can systematically manage the risks by undertaking the following four-step risk management process:

1. identify the hazards;
2. assess the risk associated with the hazards;
3. control the risk; and
4. review the process

When undertaking risk management, employers must give consideration to relevant Commonwealth regulation and codes of practice. If no regulation or code exists in relation to a specific identified hazard or risk, employers must choose a reliable source of guidance to follow.

Relevant Commonwealth Regulation

Part 12 of the Occupational Health and Safety (Safety Standards) Regulations 1994 specifies mandatory requirements for all employers and other duty holders in control of a construction project. Excavation to a depth of 1.5 metres and the construction of tunnels is regarded as high-risk construction work and as such further obligations apply to employers in control of a construction project.

Other parts of the regulations may also apply to excavation work:

• Part 2 Competency Requirements
• Part 3 Occupational Noise
• Part 4 Plant
• Part 5 Manual Handling
• Part 6 Hazardous Substances
• Part 8 Storage and Handling of Dangerous Goods
• Part 10 Electricity
• Part 13 Falls from 2 metres

Relevant Commonwealth Codes of Practice

In particular, the Approved Codes of Practice for:

Occupational Health and Safety Competency Standards for the Operation of Load shifting Equipment and other Types of Specified Equipment

• Manual Handling
• Noise
• Protection of Workers From the Ultraviolet Radiation in Sunlight
• Vibration
• Control of Workplace Hazardous Substances
• Control of Carcinogenic Substances
• Asbestos
• Synthetic Mineral Fibres (SMF)

Relevant Guidance Material

• Code of practice for Excavation - NSW Workcover 
• Code of practice for Excavation – Victoria Worksafe
• Building Code of Australia

• SAI Global provides access to many Australian and international standards & technical information on excavations. You can access SAI Global on-line at www.saiglobal.com.au/shop.

Safe Excavation Work Essentials

CONSTRUCTION workers make up only 6 percent of the total workforce, but they are involved in more than 20 percent of all work-related fatalities. Trenching accidents that are directly related to excavation work account for almost 200 deaths annually. Construction workers are buried, and they die from suffocation. It is almost impossible to escape once a cave-in occurs because soil weighs about 100 pounds per cubic foot.

Investigations indicate that improper planning, failure to recognize potential safety problems, and/or the lack of a formal excavation plan are the primary accident causes. Unsafe placement of spoil pile, operating equipment too close to the edge of a trench, improper shoring, failure to provide safe access and egress to the work area, and lack of adequate emergency rescue equipment are major contributing factors. In many cases, workers are not aware of the hazard potential or are not properly trained to identify safety issues.

Before Excavation Begins
All workers must understand the nature of the work to be performed, the procedures to be followed, and the potential hazards to be encountered before any work begins. Electrical, water, and sewer easements must be investigated and their locations properly identified.

Precautions to prevent accidental contact must be taken. All objects outside the excavation area that could cause a cave-in must be supported or moved a safe distance away. Barrier guards, signs, or flashing lights also must be provided to protect the excavation site. Access to the area must be restricted to workers.

When workers are required to enter an excavated area that is more than 4 feet deep, confined space safety rules must be followed. These rules require preliminary monitoring in the work area if breathable air contamination or a hazardous atmosphere is suspected.

When contamination exists, monitoring results must be posted at the work site, and an entry supervisor must issue a work permit. The permit must outline the work to be performed, potential hazards, and approved work procedures.

All confined space work team members must be identified. Team members include an attendant who enforces the work permit, entrants who do the work inside the work space, a rescue team that is on stand-by status in the event of an emergency, and an atmosphere evaluator who monitors contamination in the work space.

The permit must be posted at the work site. Stand-alone rescue equipment also must be immediately available, and rescue team members must be trained in emergency rescue techniques. The attendant cannot perform rescue operations; all rescuers must be respirator-certified. At least one person must be trained in cardiopulmonary resuscitation techniques.

* No work should be performed on the faces of sloped or benched excavations above workers without protecting workers at the lower levels.

* Drainage must be provided whenever work is performed in excavations where water is accumulating or can accumulate.

* Stairways, ladders, and/or ramps must be provided in all trenches that are 4 feet deep or deeper. Means of access/egress must be positioned so they are no more than 25 feet from any worker inside the work area. Earthen ramps are acceptable for egress only if a worker can use them while walking in an upright position.

* Guardrails must be provided on walkways or bridges that cross excavations that are more than 6 feet deep.

* Reflectorized or warning vests must be worn by all workers when vehicular traffic is present or in close proximity to the excavation site. It also may be necessary to provide traffic control in busy work areas.

Excavated Materials
All excavated materials must be set back at least 2 feet from the excavation area to prevent possible cave-ins. When the proper setback cannot be provided, materials should be hauled away. Excavation equipment should not be operated or stored where it can create a potential cave-in problem.

Safe egress or rescue operations should not be blocked by materials or equipment stored outside the work area. A clear path of egress from the work area must always be maintained.

Work Site Inspections
Work site inspections must be conducted by a competent person on a daily basis before work begins. Inspections also are required throughout the work shift, as needed, to ensure proper safety conditions are maintained. Other inspections must be conducted after each rainstorm or hazardous occurrence.

The competent person must have training in soil analysis, the use of protective systems, and rescue procedures. He/she must understand OSHA safety requirements and have the authority to stop work immediately when a hazard develops. Use an inspection checklist such as this one to ensure standardization of all inspections:

Excavation Work (Daily Inspection Checklist)

Excavation Work Site
Has work site been inspected by a competent person?
Does he/she have the authority to stop work?
Are all workers wearing hard hats?
Are spoils, materials, equipment set back 2 feet?
Are barriers provided? Are walkways equipped with guardrails?
Are workers protected from suspended loads?
Are all warning devices/systems operational?

Utilities
Have utility companies been contacted? Utilities located and marked?
Were workers advised of potential hazards? Are procedures being followed?
Have underground installations been protected?

Wet Conditions
Is water buildup controlled? Is removal equipment monitored?
Are access/egress routes protected? All inspections completed?

Hazardous Atmosphere
Has the atmosphere been tested for contamination?
Is the oxygen content 19.5 percent to 21 percent?
Is forced air ventilation provided to prevent buildup of flammable gas?
Has monitoring been conducted to ensure the work area remains safe?
Is emergency rescue equipment available? Rescuers trained?
Are rescue drills conducted? Rescue team on stand-by status?
Are safety harnesses/life lines individually attended?
Have all safety issues been addressed?

Soil Classifications
* Stable rock: natural solid matter that can be excavated with vertical sides and remain intact while exposed.
* Type "A" soil: cohesive soil with an unconfined compressive strength of 1.5 tons/sq. ft. (TSF) . . . clay, sandy clay, hardpan
* Type "B" soil: cohesive soil with an unconfined compressive strength greater than 0.5 but less than 1.5 TSF . . . silt, sandy loam
* Type "C" soil: cohesive soil with an unconfined compressive strength of 0.5 TSF or less . . . granular soils, sand, loamy sand

Maximum Allowable Slopes
Maximum allowable slopes for excavations that are less than 20 feet deep:

* Stable rock: 90 degrees (vertical)
* Type "A" soil: 53 degrees
* Type "B" soil: 45 degrees
* Type "C" soil: 34 degrees

Protective Support Systems
No protective support system is necessary if the excavation is made entirely in stable rock, is less than 5 feet deep, and a competent person has found no indication of a potential cave-in. All other excavations must meet established safety standards or be approved as follows:

* Must conform to data provided by the manufacturer/supplier of the support system.

* Must meet tabulated data approved by a registered professional engineer.

* Must be designed by a registered professional engineer. All support systems for excavations deeper than 20 feet must be designed by a registered professional engineer.

Conclusion
Work inside open trenches is seldom regarded as work in a confined space until emergency escape is necessary. Potential safety hazards must be more readily recognized before work begins, and all workers must know the precautions needed to prevent accidents.

Additional awareness training is necessary. Workers who enter confined spaces are at extreme risk. They should always "look before they leap." Serious accidents are the consequence of poor planning and a lack of hazard recognition.