Dig Deep: The Ultimate Excavation Safety Guide
Excavation work involves removing soil or rocks and leaving behind an open area, a hole, or cavity. Excavation can be done manually using tools, such as on an archaeological site. Most commonly, industry uses machinery or explosives.
Excavation may be as large as an open excavation or pit excavation or as small as potholing to find an underground service. Regardless of its shape or size, any excavation of any type comes with high-risk hazards that you must account for during the planning phase.
Planning your excavation and updating your plan as conditions change is the key to OSHA compliance and excavation safety. Keep reading for a complete guide to excavation planning, safety, and management.
What Makes a Trench so Dangerous?
Underestimating the risk level associated with digging in, working in, or closing an excavation is incredibly common. It’s so prevalent that OSHA has a specific priority goal revolving around trench hazards.
Why are excavations so dangerous?
The sheer weight of the soil, rock, and debris involved is enormous. A single cubic yard of dirt or soil can weigh around a ton: though it can be more or less depending on the soil type and composition of the area. Most trenches are more than a single cubic yard, so you can imagine the inherent danger of a collapsed trench.
Some of the things that weigh a ton: 20 yards of track from the New York City subway system, an adult male moose, a live oak tree, and the Mark 84 bomb.
As a result: a trench collapse is more likely to result in recovery than a rescue.
What are the OSHA Trenching and Excavation Standards?
Both federal and state OSHAs have strict trenching and excavation requirements.
The federal OSHA standards you should refer to include:
- Scope, application, and definitions applicable to this subpart (Excavations) – 29 CFR 1926.650
- Specific Excavation Requirements – 29 CFR 1926.651
- Requirements for protective systems – 29 CFR 1926.652
Here’s what you need to know about federal OSHA:
- If your trench is greater than 5 feet deep or with unstable ground, you need a protective system (e.g., sloping, shoring, or shielding).
- If your trench is greater than 20 feet deep, then you need to go one step further. You need a registered engineer to design a protective system or find a registered-engineer-approved protection system.
- All trenches must be inspected daily and prior to worker entry.
- All trenches must feature safe access and egress within 25 feet of all workers.
Before You Dig: Excavation Preplanning and Permitting
Every excavation begins with an excavation plan.
There’s an unwritten rule that you don’t to worry about a trench or pit that doesn’t extend beyond four feet, but that’s untrue. OSHA requires you to have a plan once your trench work extends below four feet. However, every single trench benefits from a full excavation plan. This is particularly true when the excavation and trenching work could negatively impact adjacent structure stability.
What goes into an excavation plan?
It starts with a survey.
- You’ll call the 811 number for your locality to identify utilities.
- Take photographs of the area, including any structures impacted by the digging.
- Assess the task, equipment needed to complete it.
- Identify the soil type. (You may have more than one!)
With a survey in place, you will identify the “competent person” who will determine the right protective measures based on the survey. The soil type will make the biggest impact on their determinations. We’ll cover the soil type issue in more depth in the next section.
Finally, you’ll need to determine whether you need a permit to excavate. These vary depending on your state and locality.
Tip: Cal/OSHA demands a permit for any excavation reaching 5 feet depth or greater. You’ll also largely need permits for most excavations or earth moving in most major cities. Remember all permits need to be in place before you can start digging.
Understanding Excavation Hazards
Before you book an operator or pick up a shovel, you need a full risk management plan based on the survey above.
Excavation risk management tackles multiple hazards, but the most prominent and most deadly of these is an injury caused by the collapse of a trench. As Eric Voight, a member of the ANSI/ASSP A10 Committee, told the ASSP podcast team last year in Episode 46, “Nature will always try to fill in any void human puts in it.”
In other words, if it can collapse, it will. And you need to be prepared for it to prevent it.
Other excavation hazards include:
- Working with heavy machinery
- Manual handling
- Proximity to traffic
- Electrical hazards
- Underground utilities
- Falling rocks or earth
- In-rush of water
- Potential confined space hazards
- Undercutting of structures and foundations
Finally, you may need a registered professional engineer to assess any excavations next to an existing building or adjacent construction, including buildings, utilities, roads, and buried structures. They can tell you whether those structures will impact your excavation work or conversely if the excavation work could pose a hazard to those structures.
Why Dirt Is Your Biggest Excavation Hazard
The type of soil makes the biggest impact on your excavation risk. There are four types of soil classification: stable rock, Type A, Type B, and Type C. OSHA requires a competent person to classify the soil using at least one visual (e.g., examining a spoil pile or trench wall) and one manual analysis (feeling soil in your hands, using a penetrometer, etc.) outlined by OSHA or allowed by the ASTM.
If you want to skip testing, then you must assume the soil is Type C and make decisions accordingly. Type C is the least stable soil, which means you need the most protection.
The OSHA standard only requires one manual analysis, you can’t be sure of your soil type with just one test. You want multiple samples and multiple forms of testing to be clear of your requirements. What’s more, a trench may cut through more than one type of soil.
While soil type has a heavy impact on excavation, it’s important to remember that soil type is only the beginning. Other issues will arise depending on the depth of the cut, soil water content, and soil changes due to the weather.
And remember: when in doubt, operate as if you have Type C soil.
|Type A||Cohesive with high unconfined compressive strength||Clay, silty clay, clay loam, sandy clay|
|Type B||Medium unconfined compressive strength includes cohesive and non-cohesive soils||Angular gravel, silt, soils fissured or disturbed by heavy traffic that might otherwise be Type A|
|Type C||Least stable: granular soils and cohesive soils with low unconfined compressive strength||Gravel and sand|
Getting Started with Excavation Risk Management
Because any trench can collapse, you need to fit a protection system. OSHA only requires protection systems once a trench reaches a depth of five feet. However, you should consider some form of protection regardless of the depth.
OSHA uses the phrase “Slope it, shore it, shield it” to reiterate the need for protective systems.
- Sloping cuts a trench at an angle on an incline that moves away from the excavation.
- Shoring supports the walls to prevent cave-ins and soil movement.
- Shielding includes trench boxes and other supports, which also prevent cave-ins.
Your system will depend on your survey and hazard analysis. Keep in mind that you may still need benches or supports even in relatively shallow excavations. Poor soil quality can make even three-foot trenches unstable and dangerous.
You might also need to bench the excavation, which means carving steps into the slope of the excavation. The benching of a trench is used to eliminate loose gravel and soil from falling into the excavation, and it can lessen the weight of the soil in the event of a collapse. You may use benching instead of sloping, but only in unique situations when the slope angle or soil type won’t allow for sloping.
Managing Other Excavation Risks
Trench supports tend to take up most of the resources, but they aren’t the only risk management strategies needed in an excavation.
Other common forms of risk management will include:
- Diverting electrical hazards where possible
- Managing traffic (e.g., fencing off the excavation, backfilling and covering if required, etc.)
- Traffic control of roadway
- Manual handling training for workers in the trench
- Testing emergency response equipment
- Practicing emergency response procedures
Finally, OSHA regulations provide strict requirements for access and egress for excavations. Your access and egress points should meet the needs of the trench and the soil and always be within 25 feet of the workers, which means you may need more than one access point.
Remember that every trench requires an inspection before entering it. Workers should never enter the trench before a competent person signs off on the inspection.
Scheduling Excavation and Trenching Inspections
Excavation safety doesn’t begin and end with the survey, inspection, and shoring. Soil can change every day, and your work plan needs to account for changes in soil or site conditions. So, excavation inspections are an ongoing process from the day work begins until the backfill is entirely complete.
Remember: you need to inspect trenches, regardless of whether you need to shore or slope them and regardless of the risk of collapse. Not only can severe injury or death occur in a 3 1/2-foot trench, but there are more hazards outside of trench collapse.
The following work plan can serve as a baseline for an excavation that is correctly engineered and free from other major hazards, such as nearby buildings.
Tip: Any trench inspection needs to be completed by a “competent person” regardless of the depth of the trench.
How Often Do You Inspect a Trench?
Before the first person enters the trench, a competent person must evaluable the protective structures and ensure the trench is safe.
The safety team must schedule daily inspections of the trench.
Any trench should be inspected once a day before anyone accesses it. If in California and the trench is deeper than five feet, then you must inspect it before each shift. Daily inspections may be more frequent when site conditions change, such as heavy rain or during seasons when freezing and thawing occur.
A trench without any activity should be inspected once a week.
Trench inspections must also occur after:
- Any event impacting the supports
- Every rain event
- After rock or earth falls
Trench Inspection Checklist
As you inspect a trench, you must look at all areas of the trench and any other hazards related to the trench.
The following checklist is an example of what should be included in a daily inspection:
- Inspect the surface conditions.
- Are there cracks in the soil?
- Is there standing water in the excavation?
- Is the soil heap an appropriate distance from the trench (at least two feet)?
- Are there any equipment or materials near the edge of the trench?
- Assess the current and immediate past weather.
- Is it raining?
- Did it rain overnight?
- Has it frozen and unfrozen?
- Take note of the trench sides and any sloping and benching.
- Is there a change in the soil type?
- Can you spot any cracks?
- Is the slope of the side or bank appropriate?
- Evaluation access and egress.
- Are there appropriate measures for access and egress?
- Are the access and egress measures secure?
- Will every working be within 25 feet of an access/egress point?
- Inspect shoring and shielding.
- Is the shoring or shielding in place?
- Are they functioning correctly?
- Are the wedges tight?
- Examine existing utilities.
- Is the support adequate?
- Are there loose materials?
- Account for PPE.
- Is everyone who will work in or around the trench wearing the appropriate PPE? (hard hats, hi-vis vests, steel-toe boots, etc.)
- Assess atmosphere.
- If a hazardous atmosphere could occur (e.g., in a confined space), is the atmosphere tested for vapors, gasses, and high or low levels of oxygen before entry?
- Is there an emergency response plan and equipment ready in case of a hazardous atmosphere?
You may find the following resources helpful:
- Daily Inspection Checklist for Checklist/Excavation Sites – OSHA
- Working in Excavations – Frequently Asked Questions – Health and Safety Authority, Ireland
- Daily Inspection Checklist – SLAC Stanford (California)
Every Excavation Benefits from a Plan
Failing to plan for an excavation is one of the most common and dangerous mistakes anyone can make when preparing to dig a trench. Any trench, no matter how shallow, can collapse. And it’s possible to encounter hazards even in a three-foot trench.
With the right excavation plan and workflow in place, you increase your ability to remain compliant with OSHA’ strict excavation regulations. You also better protect not only the workers in the trench but anyone (or structure) who might come into contact with it.
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