Hazards Associated with Excavations & the Control Measures
Excavation is the process of digging into earth, soil or rock in order to create a space or a structure. It can also refer to the removal of material from a site, such as rubble or soil. Excavation may be done with hand tools or heavy equipment; it is most often a commercial activity.
Excavation work is done by excavators and engineering construction contractors. Building structures such as roads, bridges and buildings require excavation for the foundations and basement floors. In some cases, large-scale projects can involve the use of strip mining techniques for coal and ore mining.
In mining and quarrying operations, excavation refers to the process of removing underground waste (tailings) from beneath active workings as well as from mined-out areas in preparation for backfilling (reinstatement). Excavation may also refer to the process of removing a layer of rock or soil from the surface.
What Is Trench Excavation?
Trench excavation is the process of digging out a trench for the purpose of creating a foundation for a structure. This may include buildings, roads, or underground pipes. The trench is typically dug using shovels, but excavators can also be used to dig deeper trenches.
The first step in trench excavation is to plan where the trench will be located and what shape it will take. This is done using blueprints and surveys of the area where you want to dig your trench. After this has been decided on, you can start digging!
Trenches are dug by hand with shovels or other tools like pickaxes or hammers. Excavators are also used for this job because they can do it much faster than humans alone would be able to do it. This process usually takes several days or even weeks depending on how deep the trench needs to be dug into the ground before reaching solid bedrock below which you may have missed when surveying beforehand due to being under water at certain times during rainy seasons when rivers overflow their banks as well as other factors such as weather conditions at present time being too hot/cold etc.
What Is Shoring Excavation?
Shoring excavation is a method of digging into the ground that involves using temporary supports to keep the area from collapsing.
The term “shoring” comes from the word shoring, which refers to the use of vertical supports to hold up an unstable structure. Shoring excavation uses this technique in order to prevent cave-ins and collapses while workers are digging into the ground.
Shoring excavation can be used in a variety of situations, including when there is little or no soil support available and when there are large amounts of debris that need to be removed. It also helps prevent damage caused by subsidence (when the ground shifts), which can occur when there is too much pressure on an area.
Types Of Excavation
There are two main types of excavation: open and closed.
Open excavations are made by removing material from the ground with a machine, then piling it up in an area that has been reserved for that purpose. This can be done with a backhoe or a front-end loader. It’s common to have one worker drive the machine while another works at the front end, removing debris and making sure the hole stays clear of rocks or other obstructions.
Closed excavations are made by digging into the ground using tools like shovels and picks. This type of excavation is usually used when there is no room to pile up excess dirt safely, or when you want to keep the ground from being disturbed by heavy machinery.
Hazards Associated With Excavations
There are about seven deaths each year due to work in excavations. Many types of soil, such as clays, are self-supporting, but others, such as sands and gravel, are not. Many excavations collapse without any warning, resulting in death or severe injury. Many such accidents occur in shallow workings. It is important to note that, although most of these accidents affect workers, public members can also be injured.
The specific hazards associated with excavations are as follows:
- the collapse of the sides;
- materials falling on workers in the excavation;
- falls of people and/or vehicles into the excavation;
- workers being struck by plant;
- specialist equipment such as pneumatic drills;
- hazardous substances, particularly near the site of current or former industrial processes;
- the influx of ground or surface water and entrapment in silt or mud;
- the proximity of stored materials, waste materials, or plants;
- the proximity of adjacent buildings or structures and their stability;
- contact with underground services;
- access and egress to the excavation;
- fumes, lack of oxygen, and other health hazards (such as Weil’s disease); and
- contaminated ground.
Clearly, alongside these specific hazards, more general hazards, such as manual handling, electricity, noise, and vibrations, will also be present.
Precautions and Controls Measures for excavations
The following precautions and controls should be adopted:
- At all stages of the excavation, a competent person must supervise the work, and the workers must be given clear instructions on working safely in the excavation.
- The sides of the excavation must be prevented from collapsing either by digging them at a safe angle (between 5º and 45º, dependent on soil and dryness) or by shoring them up with timber, sheeting, or a proprietary support system. Falls of material into the workings can also be prevented by not storing spoil material near the top of the excavation.
- The workers should wear hard hats.
- If the excavation is more than 2 m deep, a substantial barrier consisting of guard rails and toe boards should be provided around the surface of the workings.
- Vehicles should be kept away as far as possible using warning signs and barriers. Stop blocks should be placed behind wheels when a vehicle is tipping materials into the excavation.
- The excavation site must be well lit at night.
- All plant and equipment operators must be competent, and non-operators should be kept away from moving the plant.
- Operators of the noisy plant must wear PPE.
- Nearby structures and buildings may need to be shored up if the excavation may reduce their stability. Scaffolding could also be de-stabilized by adjacent excavation trenches.
- Pumps can only control the influx of water after the water has been channeled into sumps. The risk of flooding can be reduced by isolating the mains’ water supply.
- Hazardous substances or health hazards should become apparent during the original survey work and, when possible, removed or suitable control measures adopted. Any such hazards found after work has started must be reported and noted in the inspection report and remedial measures. Exhaust fumes can be dangerous, and petrol or diesel plant should not be sited near the top of the excavation.
- The presence of buried services is one of the biggest hazards, and the position of such services must be ascertained using all available service location drawings before work commences. As these will probably not be accurate, specifically trained people should use service location equipment. The area around the excavation should be checked for service boxes. If possible, the supply should be isolated. Only hand tools should be used in the vicinity of underground services. Overhead services may also present risks to cranes and other tall equipment. If the supply cannot be isolated, then ‘goal posts’ beneath the overhead supply and suitable bunting and signs must be used.
- As are crossing points for pedestrians and vehicles, safe access by ladders is essential. Whenever possible, the workings should be covered entirely outside working hours, particularly if there is a possibility of children entering the site.
- Finally, care is needed during the filling-in process. Wells and disused mine shafts are found during construction work and must be treated with caution and the same way as an excavation. The obvious hazards include falling in and/or drowning and those associated with confined spaces – oxygen deficiency, the presence of toxic gases, and the possible collapse of the walls. Controls include fencing off the well and covering it until specialists have reviewed the situation. Shallow wells would normally be drained and filled with hardcore, whereas deeper ones would be capped.
Inspection and reporting requirements
The duty to inspect and prepare a report only applies to excavations that need to be supported to prevent accidental fall of material. Only persons with a recognized and relevant competence should carry out the inspection and write the report. Inspections should take place at the following timing and frequency:
- after any event likely to affect the strength or stability of the excavation;
- before work at the start of every shift; and
- After an accidental fall of any material.
Although an inspection must be made at the start of every shift, only one report is required of such inspections every seven days. However, reports must be completed following all other inspections. The report should be completed before the end of the relevant working period, and a copy given to the manager responsible for the excavation within 24 hours. The report must be kept on site until the work is completed and then retained for three months at an office of the organization which carried out the work.
5 Common Trenching & Excavation Safety Hazards
Trenching and excavating are a regular part of construction operations and are required for a wide range of construction projects. According to the Occupational Safety and Health Administration, or OSHA, trenching is a leading jobsite hazard, which causes an average of 54 fatalities each year.* Understanding the risks associated with trenching and excavating can help you prevent bodily injury and fatalities. Learn about OSHA’s common trenching and excavation safety guidelines to help protect yourself and your crew the next time you dig.
Trenching and excavating: What’s the difference?
OSHA defines excavating as “any man-made cut, cavity, trench, or depression in an earth surface formed by earth removal.” A trench is a type of narrow excavation in which the depth is typically greater than the width, which does not exceed 15 feet. According to this definition, all trenches are excavations, but not all excavations are trenches. The specific safety requirements for trenches depend on the depth of the trench.
Trenches 5 feet to 19 feet: OSHA explains that any trench other than those made of stable rock exceeding 5 feet in depth must have a protective system in place. The protective system must be implemented by a competent person. This can be any qualified worker capable of identifying rock and soil composition and hazardous excavating conditions in addition to possessing the knowledge and authority to take corrective action.
Trenches 20 feet and deeper: A registered professional engineer must implement a protective system for any trench exceeding 20 feet in depth as required by OSHA.
Top 5 excavation safety hazards
Trench collapses kill an average of two workers every month, making this a serious threat to worker safety. To prevent cave-ins, OSHA requires a professional engineer or a qualified professional to analyze soil composition, and then design and implement a system that:
Hiring a professional engineer or a qualified professional to design a system that prevents cave-ins is critical for preventing injury and jobsite fatalities.
Bonus tip: Because moisture and other weather conditions can affect soil stability, OSHA recommends that excavations be inspected at the beginning of each shift, after it rains, or after other extreme weather events.
2. Falls and falling loads
Workers and work equipment can fall into an excavated area. When possible, install a barrier and safety signage around the perimeter of the excavation to clearly mark the fall hazard. Falling loads, such as jobsite equipment or excavated dirt, can also fall into a trenched area and crush anybody who is working below. This is why OSHA requires jobsite materials to be stored at least two feet away from the edge of an excavation. Additionally, OSHA recommends that employers do not allow work to be conducted beneath suspended or raised loads.
3. Hazardous atmospheres
Trenched areas sometimes have depleted oxygen levels, which is safety hazard that must be taken into consideration on excavation sites. The atmosphere in trenched areas can also be contaminated by toxic gases and chemicals. For these reasons, OSHA requires atmospheric testing to be performed by a qualified professional in excavations that exceed four feet. If atmospheric hazards are present, then workers must wear the appropriate respiratory protection equipment depending on the hazard in the excavated area.
4. Mobile equipment
Accidents involving construction vehicles, such as dump trucks or backhoe loaders, are a common hazard of trenching sites. Mobile equipment operators might have an obstructed view and therefore be unable to detect when they are approaching the trench perimeter. OSHA suggests that a spotter or a flagger be designated to direct the mobile equipment operator and prevent the vehicle from falling in the trench. When material is being loaded or unloaded from the construction vehicle, workers should be required to stand back in order to prevent being hit by flying debris.
Bonus tip: Wearing the right protective apparel will minimize the risk of working around mobile equipment. Make sure to wear a reflective vest to make yourself more visible to mobile equipment operators, and wear a hard hat to protect your head from construction debris.
5. Hitting Utility Lines
In addition to causing expensive damage to municipal infrastructure, hitting utility lines when digging can also cause electrocution and natural gas leaks,which can lead to worker fatalities. Fortunately, you can easily avoid hitting utility lines by contacting your local utility companies before you dig. Simply call your local 811 agency and allow the required time for the utility companies to mark their lines. Not only will this keep your crew safe, but this will help to prevent your company from being fined since digging without calling is illegal in many states.
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*According to the U.S. Bureau of Labor and Statistics, reported by the National Institute for Occupational Safety and Health
Excavation Risk Assessment
A risk assessment of excavation is a critical part of the planning process for any excavation project. This document aims to identify, analyze, and prioritize the risks associated with an excavation so that those involved in the project can make informed decisions about how to mitigate them.
Below are some of the risks we’ve identified:
Slippage is when loose soil or other material falls away from the edge of an excavation site. It can cause damage to surrounding property and equipment, as well as injury to workers on site.
Falling objects – Objects that have fallen into an excavation site can cause damage to surrounding property and equipment if they aren’t removed quickly enough. Additionally, workers may be injured if struck by falling objects.
Sinking or shifting structures – If nearby structures shift or settle due to heavy equipment being used at an excavation site, damage could result for both equipment operators and people working in nearby buildings.
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I never thought about how many things actually come into play during an excavation. You’re right when you said that any water that can come into the site needs to be pumped with the necessary equipment. I’m planning on starting my own fishery and we’ll have to do some excavating to flatten the property I bought. Since we’re working near a body of water, it’ll be important for me to get a commercial excavator who has the equipment to safely do just that.
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