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Excavation hazards control measures

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Excavation hazards control measures related to excavation work represent a high percentage of serious or fatal accidents, one of the main causes being burial caused by the cave-in. Burial accidents are always present in excavation work. Hence the urgency of identifying the depth of the danger and evaluating the risks that the workers face.

According to the Occupational Safety and Health Administration (OSHA), trenching causes an average of 54 worker deaths annually, so it is necessary to know the Excavation hazards control measures if this is your job.

OSHA defines an excavation as “any man-made cut, cavity, trench, or depression in a ground surface formed by earth removal.” Trenches are a type of narrow excavation, which is usually done deep for different purposes. Excavations are the process by which quantities of earth and natural elements are removed from a piece of land, to start a construction or foundation. Excavation hazards control measures

The objective is to remove a certain amount of soil or earth through manual processes (pick and shovel) or with mechanical tools (excavators, backhoes, electric hammers). This will depend on the type of excavation, whether it is deep or shallow and the type of soil. At the end of this post, we will analyze the types of soil that we completely understand the Excavation hazards control measures. Excavation hazards control measures

Excavation hazards control measures list

When talking about Excavation hazards control measures, there are many risks that workers are exposed to:

  1. Cave-ins: Cave-ins in excavations are estimated to kill an average of two workers each month. This is why OSHA recommends that workers have qualified specialists to analyze the composition of the soil.
  2. Falls and falling loads: Both workers and work equipment are at risk of falling through the opening on the floor.
  3. Hazardous Atmospheres: On some occasions, excavations of great depth may have low oxygen levels, as well as may be invaded by toxic gases and chemicals.
  4. Underground utilities: Sometimes there is a chance of contact with underground utilities such as water and gas pipelines, electrical cables etc.

During the excavation work, a cave can be generated, as a result of the loss of cohesion between the particles. For this reason, it is essential to consider the risks that arise in these tasks, take the corresponding safeguards and avoid accidents in our workplaces. The other most important risks in carrying out work in excavations except cave in are:

  • Falls of personnel at the same level.
  • Personnel, materials and vehicles fall into the excavation.
  • Contact with underground utilities (electricity, gas, water, etc.).
  • Overturning of machinery.
  • Hits with vehicles.

To help you prevent any type of incident, we present a list where we identify the most common dangerous actions and conditions in this type of operation.

Excavation hazards control measures
Excavation hazards control measures

Dangerous acts during excavation

  • Failure to identify the presence of water, gases or existing underground utilities (electric, gas). Excavation hazards control measures
  • Massive excavations or trenches, do not have proper means of access and egress.
  • Not having hard barriers that prevent the proximity of works or traffic less than 2 m from the upper edge of the excavation. Excavation hazards control measures
  • Excavate without knowing the natural angle of repose of the ground
  • Lack of signage, warning light and flagman. Excavation hazards control measures

Dangerous conditions during excavation

  • Uncontrolled slope angles
  • Lack of shoring systems (if necessary)
  • The proximity of dynamic loads to the edge of the excavation (presence of vibration due to transit in the perimeter)
  • Lack of soil mechanics study
  • Not having lifelines or anchor points above the excavation, for vertical rescue use
  • Presence of vehicles and machinery in the area near the works (less than 2 meters from the excavation).
  • Absence of signage that informs about the movement of machinery and the departure of trucks.

Excavation safety precautions

During the excavation work, material detachments can be generated, as a result of the loss of cohesion between the particles. For this reason, it is essential to consider the risks that arise in these tasks, take the corresponding safeguards and avoid accidents in our workplaces. For this reason, we invite you to take into account these simple tips that will help you work better and safer. Excavation hazards control measures

Before starting the excavation

  • Have on-site the plans of previous installations and constructions to know the layouts of underground electrical or gas lines.
  • Review in the soil mechanics studies the maximum angle of inclination of the slope if any shoring system or protection of the walls of the excavation is indicated.
  • Train workers on the risks to which they are exposed on the job, and the correct work methods, procedures and personal protection elements to use.
  • Install the hard barricade, which should be at a distance greater than half the depth of the excavation. Excavation hazards control measures
  • Install the corresponding signage at the work site that indicates the risk of falling in all open excavations in sectors of pedestrian traffic. Excavation hazards control measures

 

  • Carry out tasks with vibration at a minimum distance of 1.5 times the depth of the excavation. Special care must be taken when compacting the bottom and edges.
  • The edges of the excavations must be kept clean and tidy.
  • Deposit the extracted material at a distance equal to or greater than half the depth of the excavation, with a minimum of 0.6 meters. Toe boards must be installed in case of the danger of materials falling into the excavation.
  • Control the traffic on the upper edge of the excavation while the stability and capacity to receive overload are not defined. Excavation hazards control measures
  • Assess if a pump system for water extraction is necessary.
  • Evaluate if natural light is sufficient or if it is necessary to install a warning light.
  • Write an emergency procedure that allows timely assistance in the occurrence of an accident, which must be evaluated periodically.
  • Use a checklist. Excavation hazards control measures
  • A brief TBT/LMRA before the work commence so that workers understand the hazards and precaution which is mentioned in formal job safety analysis/ risk assessment or hazard assessment control form. Excavation hazards control measures

Safety during the excavation

Excavation hazards control measures
Excavation hazards control measures

And, as it is necessary to prevent work with the greatest safety, it is necessary to have the best team of experts to safely diagnose what their morphological characteristics are, the possibilities they offer or the impediments that should not catch you off guard.

  • Operators working in trenches should keep a distance from each other to prevent them from hitting each other with tools while working. This distance must be at least two meters.
  • If, when digging, a sudden change in the characteristics of the soil is perceived, or sand and gravel banks, dumps, or any other accident appears, the work should not be continued until specialized personnel indicate the measures to be adopted.
  • If elements with combustion engines are used in excavations, adequate ventilation measures must be taken.
  • Permanently check the condition of cords and power tool handles.
  • Do not use power tools or extension cords if there is water inside the excavation.

Worker and Staff protection

When carrying out excavation work, certain aspects must be taken into account that can influence the safety and health of workers. Know the dangers and preventive measures that must be applied to avoid accidents.

  • Workers who work in excavation tasks must use basic personal protection elements, such as safety shoes, helmets with chin straps, gloves, sun protection and eye protection.
  • When the work is carried out on the edges of excavations deeper than 1.5 meters and there is a risk of falling into it, workers must use a body harness-type safety belt secured to a supporting structure.
  • When working in the presence of water or mud, rubber boots with a safety toe should be used.
  • When using a breaker hammer hearing protectors must be used, not allowing the use of an earplug.
  • Workers who work in excavations near vehicle traffic routes must wear a reflective vest.
  • Signalmen must wear a reflective vest at all times.
  • Workers who are manoeuvring boom lifts, winches or sheaves to extract material from inside the excavation must always use a harness-type safety belt, tied to a lifeline anchored to a resistant point independent of the work structure.

Reviews and controls

And, as it is necessary to prevent work with the greatest safety, it is necessary to have the best team of experts to safely diagnose what their morphological characteristics are, the possibilities they offer or the impediments that should not catch you off guard.

  • The supervisor in charge must carry out a daily review of the upper edge of the excavation when it does not have shoring, to warn of the possible appearance of cracks that may indicate a possible fault in the ground.
  • Inspect the excavations and shoring after a storm, earthquake or another event that endangers the site or any part of it and the protections must be increased if necessary.
  • Daily, the supervisor must check the reinforcements, and wedges of shoring to ensure that they maintain their structural characteristics.
  • Review the excavations and shoring by specialized personnel before resuming work after a prolonged period of work stoppage.
  • Supervisors and workers should inspect walls for clearance of large stones, debris, or other heavy objects that could fall inside. If these conditions exist, adopt all measures for the protection of workers.

Use of machinery

  • Operators must be trained and certified to operate assigned machines and must hold the appropriate class driver’s license. Excavation hazards control measures
  • The driver of the vehicle must leave the cabin during the loading task if it is not properly protected. Excavation hazards control measures
  • When excavation is carried out using a mechanical shovel or backhoe, a safety zone must be established around the machine that is 1.5 m higher than the turning radius of the arm. The transit of people must be prohibited.
  • All heavy machinery that works in excavation tasks must have a lighting system, backup alarm and horn. The backup alarm must work automatically when you carry out this type of manoeuvre and the horn must be used to warn of any other type of unexpected manoeuvre or as a warning or danger signal.
  • There must be a flagman who directs the movement of heavy machinery using flags or colour palettes, who must be visible at all times by the machine operator and warn of any possible danger. Excavation hazards control measures
  • A flagman must be available especially when the machine approaches the edge of the excavation or the overhead electrical cables.

Access to the excavation

To control the risks related to the movement of people within the excavation site, accesses and structures that support movement on site ladders, scaffolding ladders, ramps and walkways must be considered.

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Ladder

Ladders must be available and installed every 30 meters if the excavation depth is less than 1.2 meters. If the depth is more than 1.2 meters ladder must be available every 7.5 meters. Ladders must maintain the proper slope, be tied up or down to prevent slipping, and comply with the design defined in the standard.

Excavation hazards control measures
Excavation hazards control measures

Workers must go up or down with their hands-free and maintain 3-point contact. To reach heights greater than 3 m, the stairs must be provided with handrails and toe boards. In addition, it is suggested to build breaks every 3 m and install scaffolding tower access if the depth is greater than 5 m. Excavation hazards control measures

Lightning:
  • In the case of low visibility or at night, they must be signalled using flashing pilots, provided that the circulation of personnel or vehicles is foreseen in the vicinity.
  • Whenever the passage of pedestrians or vehicles is anticipated, the fences will be illuminated every 10 m with portable light points.
  • When lighting is required inside, it will be done using external lighting towers.
  • If portable lighting is used inside, it must be powered at 24 Volts.

 What do shoring benching and sloping refer to?

  1. Excavations with the natural slope: The natural slope is the maximum inclination or slope (angle with the horizontal) that a soil wall can maintain without collapsing, ensuring static and seismic stability. (see details below – types of soil)
  2. Benching: Benching is a method of protecting employees from cave-ins by excavating the sides of an excavation to form one or a series of horizontal levels or steps, usually with vertical or nearly vertical surfaces between levels. There are two basic types of benches, single and multiple. Subsequent benches can be up to a maximum of 5 feet vertical in Type A soil and 4 feet in Type B soil up to a total trench depth of 20 feet. For Type B soils, trenching is permitted only in cohesive soils. Type C benching is not allowed at any time.
  3. Excavations with shoring: Shoring systems are temporary and flexible containment structure that can be partial or total and that allows excavation with vertical walls.

The use of shoring is required when

  • Some factors can affect the stability of the ground, for example, water, vibration or overload. Excavation hazards control measures
  • There is no space to generate the slope angle for the soil type.
  • There is little soil cohesion. Excavation hazards control measures

What are the 4 types of soil?

Employees working on excavations must be trained in all four classifications of soil: stable rock, Type A, Type B, and Type C. In general, stable rock is not common because we disturb it when excavating, leaving us with the following three types of soil to measure our excavations.

Excavation hazards control measures
Excavation hazards control measures
Type A soil

This is the most stable of the soil classifications and implies that it has a slope angle of a 3/4:1 ratio, meaning that for every foot of depth, the sides of the excavation will slope backwards three-quarters of a foot or an angle of 53 degrees. Type A flooring can also be “benched” or set at specific angles for employee protection.

 

Type B soil

This soil is less stable than the Type A soil type, but it is very cohesive and still quite stable. The slope angle for a Type B excavation is a 1:1 ratio or a 45-degree angle. For every foot of depth, the sides of the excavation should slope back 1 foot.

Type C

Of all the soil types, this is the least stable and most dangerous and should have a 1-1/2:1 slope or 34-degree angle. Depending on water saturation or seepage, angles may need to be greater than 34 degrees for employee safety. Excavation hazards control measures

Slope Angle Calculations

Determining the angle of your slope is not complicated you don’t even need a protractor. As an example, let’s calculate the slope angle of a simple trench 6 feet deep by 2 feet wide, taking into account the type of soil. Excavation hazards control measures

  1. Type A: (6 ft. x 2) x 0.75 + 2 ft. = 11 ft. wide at top.
  2. Type B (6 ft. x 2) x 1 + 2 ft. = 14 ft. wide at top.
  3. Type C (6 ft. x 2) x 1.5 + 2 ft. = 20 ft. wide at top.
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