TRENCH SAFETY IS NOT JUST A CHECKLIST

Done Daily

The condition of soil surrounding trenches and shafts can change quickly due to the soil drying out, changes in the water table or water saturation of the soil. Make sure

the soil condition and the state of shoring, battering and trenches walls is frequently checked for signs of earth fretting, slipping, slumping or ground swelling. Where

necessary, repair the excavation or strengthen the shoring system from above before allowing work

below ground to continue.

Ask and CONFIRM1. Have all underground services been located?

Before digging starts, make sure you know the exact location of any underground electrical cables, gas lines, water, sewerage and telecommunications cables. Do not rely solely on site plans and drawings as these are sometimes not accurate or complete.

2. Is earthmoving plant being used safely?

Check that plant operators are appropriately qualified. Look for qualifications endorsed with LL (for front-end loaders), LB (for front-end loader/backhoes), LS (for skid-steer loaders), LE (for excavators), LD (for draglines) or LZ (for dozers). Check that operators are not undermining existing buildings or temporary structures such as scaffolds and falsework. Make sure spoil is being kept at least a half metre back from the edge of trenches and that earthmoving plant is a safe distance from the edge of excavations. Make sure unattended front-end loaders, backhoes and excavators are always left with the bucket fully lowered to the ground. When parked overnight alongside roads or on other public space, make sure earthmoving plant is locked up and barricaded with warning lamps to alert traffic.

3. Are workers protected from trench collapse?

Never allow workers to enter a trench or shaft which is greater than 1.5 metres deep unless it has been safely battered back, or it has been properly shored, or the workers are fully protected within a trench shield. Shoring should be positioned and fixed from above; never from below. All timber used in ground support should be at least F8 grade hardwood. Never use softwood because this can fail suddenly without warning, whereas hardwood will start to creak loudly when it is becoming overloaded, warning workers to leave the trench immediately. Make sure all workers in excavations always wear safety helmets.

4. Are confined space written precautions needed?

Where there is any possibility of a hazardous atmosphere within an excavation, the extra precautions for entry into confined spaces must be put in place.

5. Are people safeguarded from falling into excavations?

Make sure trenches, shafts and excavations are properly barricaded, covered or isolated to prevent people falling into them. Whenever an excavation is to be left unattended, make sure it is secured to prevent children or other people from wandering into danger.

6. Is there safe access to trenches and shafts?

Never allow workers to climb up and down the soldier sets used in trench shoring, because they can loosen or damage the support system, triggering a trench collapse. Make sure industrial-grade portable ladders are used to gain access to the excavation floor.

7. Is someone else always present when a worker is below ground?

Never allow anyone to work alone in a trench or shaft. Make sure there is always another person close by who can provide help or get help if necessary.

8. Are open excavations being regularly inspected?

The condition of soil surrounding trenches and shafts can change quickly due to the soil drying out, changes in the water table or water saturation of the soil. Make sure the soil condition and the state of shoring, battering and trenches walls is frequently checked for signs of earth fretting, slipping, slumping or ground swelling. Where necessary, repair the excavation or strengthen the shoring system from above before allowing work below ground to continue.

Soil Mechanics

In trenching and excavation practices, "soil" is defined as any material removed from the ground to form a hole, trench or cavity for the purpose of working below the earth's surface. This material is most often weathered rock and humus known as clays, silts and loams, but also can be gravel, sand and rock. It is necessary to know the characteristics of the soil at the particular job site. Soils information is used by contractors and engineers who are trained to identify the proper safety protective devices or procedures needed for each situation. Soil is an extremely heavy material, and may weigh more than 100 pounds per cubic foot (pcf). A cubic yard of soil (3 ft x 3 ft x 3 ft), which contains 27 cubic feet of material, may weigh more than 2,700 pounds (lbs). That is nearly one and a half tons (the equivalent weight of a car) in a space less than the size of the average office desk. Furthermore, wet soil, rocky soil or rock is usually heavier. The human body cannot support such heavy loads without being injured.

DO YOU HAVE WRITTEN DOCUMENTED PROOF

Conditions that Increase the chances of a Cave In

• Lack of, or to much moisture

• Additional weight of

- spoil pile

- tools or equipment

• Unsupported faces

• Unsupported structures

SOMEONE YOU KNOW WILL DIE IF YOU ARE WRONG

A person buried under only a few feet of soil can experience enough pressure in the chest area to prevent the lungs from expanding. Suffocation can take place in as little as three minutes. Heavier soils can crush and distort the body in a matter of seconds. It’s no wonder trench accidents involve so many deaths and permanently disabling injuries.• OH&S classifies soils into four categories: Solid Rock, Type A, Type B, and

Type C. Solid Rock is the most stable, and Type C soil is the least stable. Soils are typed not only by how cohesive they are, but also by the conditions in which they are found. Stable rock is practically unachievable in the excavation of a trench. This is because the excavation of rock typically requires drilling and blasting, which fractures the rock, making it less stable. Type A soil can be clay, silty clay, or sandy clay.

A soil cannot be considered Type A if it is fissured (cracks) or other conditions exist that can adversely affect it, such as:• subject to vibration from heavy traffic, pile driving, or similar effects

• having been previously disturbed/excavated

• where it is part of a layered system, where less stable soil is near the bottom of the excavation, with the more stable soils on top.

• subject to other factors which would make it unstable-such as the presence of ground water, or freezing and thawing conditions.

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Diagram of a cave in

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Look for Potential Problems

• Fissures

• Cracking

• bulging or separation of soil

• Surface water near excavation

• Water accumulation in excavation

• Soil that has been previously disturbed

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Protective Systems

• “a method of protecting employees from cave-ins, from material that could fall or roll from an excavation face or into and excavation, or from the collapse of adjacent structures. Protective systems include support systems, sloping and benching systems, shield systems, and other systems that provide the necessary protection”

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What are our Options?

• Sloping, or Benching

• Use support systems in accordance with requirements set forth in the standard.

• Purchase an engineered system, (example..a trench box or shield.)

• Have a PE design a shielding or shoring system specific to your task.

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Sources of Vibration

• Traffic

• Railroad Operations

• Heavy Equipment Operations

• Jack Hammer Operations

• Tamping Machine Operations

• Seismic activity

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Sloping in Type ‘A’ Soil

¾ to 1 (53 Deg.)

1 to 1 (45

Deg.)

Sloping in Type ‘B’ Soil

1 to 1 (45 Deg.)

1 ½ to 1

(34 Deg.)

Sloping in Type ‘C’ Soil

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Can an Excavation be a Confined Space…?

• Oxygen deficient atmospheres: less than 19.5% oxygen.

• Potential for other gasses or Hazards to be present include but not be limited to:

- Natural Gas from potential leaks or cut lines.

- Methane from decayed matter.

- welding/ cutting operations

- combustion engines

- Electrical utilities

- application of coatings, or paint