When OSHA Comes Knocking, Preplanning Reduces Headaches and Fines

May 1, 2000

All of us have read about excavation cave-ins resulting in injuries, and we intuitively know that working inside deep trenches or pits is dangerous. It is often assumed that these injuries are the normal costs of doing business within the excavation industry.

Personal injury is only one aspect of the “costs” associated with unsafely executed earthwork. Schedule slippage and delays from sidewall collapse, runoff inundation, or damage to utilities/surface structures are far more frequent and costly to excavators than the publicized injuries in the news. In addition, the hidden costs of inspection fines levied by the Occupational Safety & Health Administration (OSHA) and the accompanying bad publicity make it apparent that proper safety planning prior to breaking ground is essential, both for the health of employees and the long-term viability (and profitability) of your company.

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Why do so many excavation contractors fail to properly preplan? One reason is tradition: Excavation is a simple activity; it has always been done in the same way, so no additional time during the up-front project design or planning phase is invested. Every time a project crew is allowed to “work it out” in the field and no one gets hurt and OSHA does not show up, this traditional view is reinforced. Then when something does go wrong, resulting in delays, injuries, or citations, it is written off as an unavoidable project loss, and work continues with the belief that the profit will be made up on the next project. The realization never occurs that these project losses were avoidable and that properly performed and implemented preplanning would have prevented these losses and padded the project’s bottom line. In summary, excavation-safety preplanning and execution simply make good business sense.

OSHA Requirements

Excavation-safety preplanning begins with a review of OSHA’s excavation standard, 29 CFR 1926.650-.652, Excavations (Subpart P). The standard contains many different requirements, as well as several appendices, that make it very confusing at first glance. The following information summarizes the main requirements in order to help contractors prepare for expected or surprise OSHA inspections.

Prior to digging, the contractor shall identify and locate all underground utilities. This requirement is to prevent backhoes and excavators from accidentally severing telephone, data, water, or gas lines. Should this occur, disruption of local services and lost project profit are the best results that can be hoped for. Equipment-operator injury is a more serious outcome if a gas explosion occurs.

All surface “encumbrances”-signs, trees, fences, poles, sidewalks, etc.-must be protected during the dig. Since undercut items suddenly can give way, striking employees and bringing down electrical lines, compliance with this requirement prevents injury or electrocution.

All excavating equipment must maintain a minimum of 10 ft. from overhead power lines rated 50 kV or less, with 0.4 in. of clearance added for every kV over 50. Adherence to this requirement will prevent the equipment from contacting the energized line, and it will minimize the possibility of electrical arcing.

Employees exposed to vehicular traffic must wear a high-visibility vest, and the excavation must be protected from traffic. If vehicular movement around the excavation edge presents the possibility of running into the hole, or if the equipment operator does not have a clear view of the edge, then stop logs or other physical barriers should be placed far enough back from the edge that impact with them will alert the operator to stop the equipment.

Any excavation left unattended must be barricaded, fenced, or otherwise protected against accidental entry from pedestrians. If the excavation is in a remote location where visitation by residents is unlikely, a barricade of posts and warning tape, with a sign, is sufficient. If the excavation is in a traveled area, however, a physical barrier such as a fence must isolate it. In these locations, an excavation left unattended is considered to be an “attractive nuisance”-a legal term that implies a responsibility of the hazard creator to physically prevent entry by the public.

The contractor must designate a competent person to assess the excavation and determine that it is safe for project personnel to enter and work. This person must be present on-site when the excavation is entered, to assess the excavation daily, as well as after each significant weather event or hazard-increasing occurrence that could affect the excavation’s safety. Sidewall exposure to drying can change excavation conditions, rain or runoff can enter the excavation, or cracking and spalling of the excavation sidewalls can occur at any time. Additionally, site activities such as pile driving, jackhammering, or other vibration-inducing tasks could cause cracking or sidewall instability. A “competent person” is, by OSHA definition, someone who is capable of identifying existing and predictable hazards in the surroundings or capable of identifying working conditions that are unsanitary, hazardous, or dangerous to employees and who has authorization to take prompt corrective measures to eliminate them. The designated competent person must understand the responsibility that this role carries. The competent person is responsible for the safety of all excavation workers and typically will be the first employee interviewed by OSHA during an accident investigation. The lack of a designated, trained, competent person available during an OSHA inspection will frequently result in a citation.

The competent person may have gained this knowledge through prior field experience, completion of formal safety training, or both. The individual designated as the competent person must willingly accept this role. Given today’s emphasis on time and schedule, this regulation is very logical. It is one of the most important of all the OSHA regulations, yet it is frequently neglected by many small contractors. Without a knowledgeable onsite authority figure, safety just isn’t going to happen.

The contractor must provide a safe means of entering or exiting any excavation over 4 ft. deep. Potentially acceptable methods are ladders, ramps, manbaskets, or stairs. This makes sense; think about how you would get into a trench without a ramp or a ladder. You would sit down on the edge and slide in, or jump down. Jumping is dangerous, and sliding places pressure on the sidewall. And when exiting, you would have to place your arms up over the surface and attempt to sling your legs over the lip. Again, you are placing pressure on the sidewall face and generating vibration, both of which are known to cause cave-ins. If you are using a straight ladder, make sure that the ladder extends out of the excavation at least 3 ft. This allows the user to climb out of the excavation and step off onto the surface instead of having to partly climb out. If you are installing a ramp, cut the ramp at such an angle that workers can easily walk out, upright, without using their hands to secure their position.

A means of egress shall be located within 25 ft. of the worker(s). This means that any excavation worker must be able to reach the provided means of exit by moving laterally no more than 25 ft. The rationale for this requirement is that in the event of a cave-in, it is critical that the worker exits within a few seconds since there is often a second (or even third) successive cave-in. Also, having the means of exit close at hand lowers the probability in long trenches that a collapse of the sidewall will block the exit travel path. If the excavation is longer than 50 ft. and workers will be moving throughout the length, then more than one exit point will be necessary: a frequently unplanned for, and often cited, requirement.

If employees must cross over the open excavation (trench), a safe means shall be provided so that the employees do not have to jump. An obvious requirement, and one that is often ignored. If a trench is 100 ft. long and employees will have to move about on both sides, they are not going to walk around the end-they are going to step or jump across. This is dangerous and can be prevented easily by placing a suitable wooden walkway across the trench. If, however, employees must cross over an open excavation at a height of 6 ft. or more, a walkway with standard guardrails (toprail 39-45 in. high and midrail halfway down) must be provided.

No workers shall enter or work in excavations where standing water is visible unless adequate protection is afforded. The presence of standing water indicates that at least part of the excavation floor and probably the lower sidewalls are saturated and thus have a diminished degree of soil cohesion-a prime candidate for a cave-in. The water must be pumped out before workers enter. Rainwater runoff can be prevented from entering in the first place by scraping some initial spoil to form diversion dikes along the outside border. Also, saturated soils are Type C (see below) by definition.

The removed spoil shall not be stockpiled closer than 2 ft. from the excavation’s edge. There are several reasons for this direction: (1) placing the spoil at the edge hides the adjacent surface and makes visual detection of cracks impossible; (2) spoil too close to the edge permits soil, rocks, debris, etc. to fall in the excavation and on top of workers; and (3) the weight of the spoil pile will place a tremendous additional downward force on the already unsupported excavation sidewall, increasing the possibility of failure.

In excavations over 4 ft. in depth, a potential for the accumulation of hazardous gases or vapors exists. Sources of hazardous atmospheric contaminants include the exhaust of equipment in or near the excavation, lateral movement through soils of natural gas, gas-line ruptures, and landfill gases (when excavating in landfills). If there is any reason to suspect that a toxic atmosphere is, or is likely to be, present in the excavation, then the atmosphere must be tested prior to working in it. A multigas monitor (oxygen, flammability, and carbon monoxide) would be appropriate for most situations if testing is required. Document the time, location, tester, and readings. The reason that pits and trenches are potential contaminant traps is because most harmful gases and vapors are heavier than air and will settle in low places, such as excavations. OSHA does not mandate that all 4-ft.-plus excavations be examined for atmospheric contaminants; it is only necessary when the possibility is real. If the excavation does contain a hazardous atmosphere, then refer to the OSHA standard, Permit-Required Confined Space, 29 CFR 1910.146, for additional requirements.

If the excavation is over 5 ft. deep, a protective system shall be employed to prevent cave-in. This requirement is the heart and soul of excavation safety and yet is the most misunderstood of all the OSHA excavation requirements. This requirement mandates that all excavations greater than 5 ft. deep be shored, sloped, or otherwise physically prevented from collapsing. It does not state that excavations under 5 ft. are always safe and need no protective system. The correct interpretation is that if project site conditions are appropriate-such as cohesive soil, lack of vibration, short-term opening, upright body positioning during work-shallow excavations under 5 ft. may not need additional protective systems, based on a knowledgeable assessment by the competent person. Historically contractors have incorrectly assumed that sloping or shoring is only required on excavations deeper than 5 ft. Since the language of the standard allows for entry into a nonshored or nonsloped excavation less than 5 ft. deep if deemed safe by a competent person, then this obviously requires a designated competent person to make that determination on-site. The contractor should be aware that many cave-ins and injuries result from shallow-excavation failures (primarily narrow trenches), and any subsequent OSHA investigation will begin with determining whether a competent person performed an assessment prior to worker entry. Therefore, written assessment notes should be maintained.

If a protective system is necessary, then sloping, shoring, shielding, or another equivalent method shall be employed to handle the soil stresses imposed. The contractor has three basic options to prevent excavation failure: (1) sloping the sidewalls such that the threat of collapse is eliminated, (2) holding back the sidewalls by installing shoring, or (3) placing a prefabricated protective metal shield (trench box) in the excavation where the workers are placed. (For detailed information on the specific requirements of sloping, shoring, or trench boxes, including engineering data, consult 29 CFR 1926.652 and the accompanying Appendices A-F.) See the sidebar for a summary of each of these options.

Preplanning: A Suggested Method

Implementation of preplanning can minimize project delays, disruption, noncompliance costs, and injuries. One method of obtaining consistency in the preplanning process is to employ a checklist at the proposal workup stage. An example of an excavation checklist follows and may be modified to suit the needs of the individual contractor. It also may be easily modified for use during the excavation as a check to verify that all proper safety measures are continuing.

It should be noted that OSHA requirements applicable to excavation work, but not contained in the excavation standard, also have been included in this worksheet. Information on the different types of soil manual field tests is contained in Appendix A of 29 CFR 1926.652 and should be read prior to attempting. If soil field classification will be performed, a pocket penetrometer should be purchased for use in determining the unconfined compressive strength.

Note: You may print out the worksheet as it appears below on this Webpage.


Project Name: Worksheet Completed By:
Project Location: Project Number:
Name of Project Competent Person:

Employee Training and Pre-Excavation Briefing

Does this job require special training: YES__ NO__

Safe excavation and rescue training conducted on: ______DATE

Mandatory pre-excavation briefing conducted on: ______DATE

Soil Classification

Will the competent person classify the soil based on its properties and site conditions?

YES__ NO__

If yes, continue. If no, then soil is assumed to be Type C; skip to Electrical Safety.

Based on visual observation, which best describes the soil in this excavation?

Stable Rock_____ Cemented Soil_____ Cohesive Soil_____

Granular Cohesionless_____ Layered System_____ Granular Soil_____

Based on visual observation, which best describes the moisture condition of the soil?

Dry Soil_____ Moist Soil_____ Wet Soil_____ Saturated Soil_____

Is a pocket penetrometer available for use on-site? YES _ NO _ N/A__

If yes, what is the average tons per square foot of the soil in this excavation? _____ tsf

Based on at least one manual test, what classification is the soil in this excavation?

Stable Rock_____ Type A Soil_____ Type B Soil_____ Type C Soil_____

What manual test was used to determine the soil type?

Plasticity_____ Dry Strength_____ Thumb Penetration_____ Other (list)________________________________________

Electrical Safety

Are all electrical devices grounded and/or GFCI protected? YES__ NO__ N/A__

Surface Encumbrances

Have all surface encumbrances that are located so as to potentially create a hazard to employees been removed or supported as necessary to safeguard employees? YES__ NO__ N/A

Underground Installations

Have the estimated locations of all underground installations been determined prior to excavation?

YES__ NO__ N/A__

Have utility companies been contacted and advised of proposed work?

YES__ NO__ N/A__

If underground installations are exposed, have they been protected, supported, or removed while excavation is open?

YES__ NO__ N/A__

Access and Egress

Are stairways, ladders, or ramps provided every 25 ft.? YES__ NO__ N/A__

Are structural ramps that are used for access and egress of equipment and/or personnel designed by a competent person qualified in structural design, and are they constructed in accordance with the design?

YES__ NO__ N/A__

Exposure to Vehicular Traffic

Are personnel who are exposed to public or project vehicular traffic wearing reflectorized or high-visibility vests?

YES__ NO__ N/A__

Exposure to Falling Loads

Are employees prohibited from standing underneath loads handled by lifting or digging equipment?

YES__ NO__ N/A__

Warning Systems for Mobile Equipment

Are warning systems utilized when mobile equipment is operated adjacent to or at the edge of an excavation?

YES__ NO__ N/A__

If yes, which type if being used?

Hand Signals_____ Stop Logs_____ Earthen Berm_____ Other (list)________________________________

Testing for Hazardous Atmospheres

Are the atmospheric hazards that can be reasonably expected to exist in excavations greater than 4 ft. deep tested and controlled? YES__ NO__ N/A__

Is testing conducted as often as necessary to ensure safety of personnel?

YES__ NO__ N/A__

Times and Readings Time: Time: Time: Time: Time:
LEL: ___% LEL: ___% LEL: ___% LEL: ___% LEL: ___%
Oxygen: ___% Oxygen: ___% Oxygen: ____% Oxygen: ___% Oxygen: ___%
Toxic: ___ppm Toxic: ___ppm Toxic: ___ppm Toxic: ___ppm Toxic: ___ppm
of ___ of ___ of ___ of ___ of ___
Special Precautions:


Emergency Rescue Equipment

Is emergency rescue equipment, such as a self-contained breathing apparatus, a safety harness and line, or a basket stretcher, readily available and attended when hazardous atmospheric conditions exist?

YES__ NO__ N/A__

Protection From Hazards Associated With Water Accumulation

Is water being controlled or prevented from accumulating in an excavation by the use of water-removal equipment?

YES__ NO__N/A__

Is operation of the water-control equipment being monitored by a competent person?

YES__ NO__N/A__

Stability of Adjacent Structures

Are support systems, such as shoring, bracing, or underpinning, provided to ensure stability of adjoining structures (i.e., buildings, walls) endangered by excavation activities? YES NO N/A

Has the support system been designed by a registered professional engineer?

YES__ NO__N/A__

Protection of Employees From Loose Rock or Soil

Are the employees protected from equipment and excavated or other material by placing this material a minimum of 2 ft. from the edge of excavations or by the use of retaining devices?

YES__ NO__ N/A__

Inspections (Use this section for safety inspections)

Are daily inspections of excavations, where employee exposure can be reasonably anticipated, being done by the competent person? YES__ NO__ N/A__

Are inspections being performed by a competent person after every rainstorm or other hazard-increasing occurrence? YES _ NO__ N/A__

Are employees removed from the excavation if the competent person finds evidence at any time of a situation that could result in a possible cave-in, protective-system failure, a hazardous atmosphere, or other hazardous conditions?

YES__ NO__N/A__

Fall Protection

Are standard guardrails provided on walkways and bridges that cross over 6-ft.-plus excavations?

YES__ NO__ N/A__

Are all excavations accessible to the public adequately barricaded or covered when unattended?

YES__ NO__ N/A__

Shoring and Other Protective Systems

Have all shoring and other protective systems been designed by a registered professional engineer or accompanied by tabulated data from the manufacturer? YES__ NO__ N/A__

Are shoring and other protective systems checked and measured each day to detect movement and possible failure?

YES__ NO__ N/A__

I have inspected the excavation described in this checklist:


(Signature of Competent Person)



Copy:  Project File



With thorough preplanning and the proper designation of a competent person, excavation work can be accomplished both profitably and safely. There is no shortcut to avoiding the scrutiny of OSHA or the occurrence of injuries. Preplanning serves as the best and only effective preparation for a surprise visit from OSHA. Completion of an excavation checklist, such as the example given, ensures that the principal requirements of the OSHA standard have been considered and addressed.

One last note: If questions concerning excavation compliance arise, do not hesitate to contact your local OSHA office. OSHA representatives are available for consultation and generally provide accurate information, and these contacts do not result in inspections (but will certainly help prevent citations if one does occur). 

Getting Down to Basics

To properly preplan any excavation, no matter how temporary or minor, there must be a basic understanding of soil mechanics, why excavations fail, and the rationale behind each applicable OSHA regulation. Once these concepts are understood, an easy method of preplanning can be used that will eliminate the hazards and injuries and their associated OSHA violations.

An excavation is any manmade cut, cavity, trench, or depression formed by earth removal. OSHA defines a trench as a long, narrow cut in the earth, where the depth is greater than the width, but the width never exceeds 15 ft. For practical purposes, it makes no difference whether the opening in the earth is called a trench or an excavation; the dangers and required safety actions are the same.

Soil Mechanics

Soil is a matrix composed of uncemented mineral grains (rocks) of varying sizes, minor amounts of organic matter, and spaces filled with water and air. The number of such spaces in soil is a function of the type of rock and organic matter and, more importantly, the history of the soil. On average, soil is about one-half air and water space and one-half rock. Because rock may weigh two and a half times that of water on a volume basis, the resulting soil matrix is extremely heavy.

One cubic foot of soil can weigh about 115 lb. when the voids are filled with water (saturated). This weight exerts pressure (stress) both vertically (equal to the weight of the soil per unit area) and horizontally (normally equal to about one-half the pressure exerted vertically). To understand how this pressure can affect a person trapped by a failed trench, consider a 150-lb. person standing on your chest. The pressure exerted would be about 300 lb./ft.3, certainly an uncomfortable situation and one that could make it impossible for you to breathe. This same pressure will be experienced by a person covered by about 2.5 ft. of soil, except this pressure would cover all parts of the body, crushing veins, arteries, tissue, and (in some cases) bone.

To understand the mechanics of an excavation failure, it helps to visualize the soil as being composed of innumerable vertical columns. Each imaginary vertical column of soil produces vertical and horizontal forces. Since the undisturbed landscape is stable, these forces must be countered by equal forces acting from opposite directions; they in fact are supplied by underlying soil or rock strata (vertical) and adjacent soil columns (lateral). The counterbalancing of these forces results in the stability of the ground surface.

With this visualization in mind, consider what happens when a vertical trench is cut. The face of the cut has now had its lateral support removed, resulting in an unbalanced or unnatural situation. To counteract the imbalance, the soil in the unsupported trench wall immediately begins movement into the trench. Although the movement may not be observable, it is only a matter of time until the trench fails. For soil to resist the forces that are pushing it into the trench, it must have some cohesion. The magnitude of the cohesion of a soil is a primary factor in determining the ability of a soil to resist the eventual trench failure. For this reason, the OSHA standard allows different sloping angles for cohesive soils depending on the inherent degree of cohesion, based on a field test that yields a conservative value for cohesion, termed an unconfined compression test.

Another primary factor in the stability of a vertical trench is water. The introduction of water (rainfall, seepage, or manmade causes) can adversely affect the ability of a trench to resist failure in two important ways.

First, saturation of the unsupported soil column can dramatically lessen its cohesion. To understand why, we need to examine what causes cohesion. The primary force that holds most soil particles together is the air and water interface between each soil particle. The resulting meniscus produces tension. When particles are completely inundated, however, the meniscus disappears and the particles float away from each other. Alternately, if soil moisture is lost through evaporation, the tension is reduced, and the holding force diminishes. Now it is easy to understand what happens to a newly exposed sidewall in any excavation. The drying actions of the sun and wind immediately begin reducing the soil moisture, until the tension is reduced to the point where cohesion is lost. At this point, any outside force, such as traffic vibration or even a footstep, will cause the dry column to fail. An equally dangerous situation is when rainfall, surface runoff, or groundwater enters an excavation, eliminating the meniscus through inundation and causing the soil to lose cohesion and float away.

To understand the second way that water reduces the ability of the trench to remain vertical, we need to understand what happens when a trench with vertical sidewalls is made. As previously mentioned, as soon as the vertical excavation is made, the unsupported soil column begins to move into the trench. Eventually, the movement causes tension cracks to form back from the edge of the trench. The formation of the tension cracks increases the likelihood of failure. When water fills these cracks, the situation is further exacerbated.

We now have discussed two major reasons why excavations collapse. Other factors contributing to cave-ins are vibration from traffic and construction equipment, unconsolidated pockets of soil and debris, downward pressure on the trench edge, and freeze/thaw.

This understanding of the mechanics of soil forces, cohesion, and failure will assist you in understanding the reasons for the various OSHA requirements and what OSHA compliance inspectors look for when they visit an excavation. The regulations applicable to excavation and trenching are contained in the federal OSHA construction standard, 29 CFR 1926.650-.652, Excavations (Subpart P). (The figures presented in this article were taken out of this standard.) Most state OSHA programs have essentially identical requirements, but if you’re digging in a “state-plan state,” you should reference its applicable excavation standard to identify any additional requirements.

About the Author

James Woolcott

James Woolcott has worked as an OSHA compliance officer, overseen hazardous-waste cleanup efforts for the US Corps of Engineers, and managed a private consulting practice. He is currently director of safety for HDR Inc. in Omaha, NE.

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