Dredging Work
Dredging Work
1.1 What is dredging work?
Excavation is defined as the removal of soil, rock or other material in connection with construction or demolition work by using tools, machinery or explosives to form an open surface, hole or cavity. Excavation includes any earthworks, drainage, cofferdam, caisson, well, shaft, tunnel or underground working.
Any construction work (including any work related to excavation) carried out in or near:
- (a) a pit, cofferdam, caisson or trench with a dredged depth exceeding 1.5 metres, or
- (b) a tunnel
can be considered 'high-risk construction work' and it is encouraged to have a safe work system or written Safe Work Method Statement (PKKS).
1.2 Who has safety and health obligations in relation to dredging work?
Employer, builder and occupant has a primary duty to ensure, so far as is reasonably practicable, that workers and other persons are not exposed to safety and health risks arising from dredging work. Duty bearers must manage the risks associated with all types of dredging at work, regardless of depth.
Self-employed person must ensure, so far as is reasonably practicable, that no person is exposed to safety and health risks arising from his work.
Client can make a significant contribution to improving the safety and health management of excavations by allocating an adequate budget for site investigations. They should be prepared to allocate additional financial resources for site investigations during construction if the expected soil or rock conditions, due to exposure during excavation, differ from those predicted in the original site investigation.
Builder has a legal duty under Part XII of the Factory and Machinery (Building Operations and Engineering Construction Works) (Safety) Regulations 1986 (BOWECS) to manage the risks associated with excavation work. For example, the builder must appoint a competent person to act as a designated person (excavation supervisor) to carry out the duties under Regulation 113(2) of BOWECS. The builder must consult, so far as is reasonably practicable, the designer of the whole or any part of the structure (permanent or temporary) on the elimination and control of risks.
Professional Engineer (PE) as a designer must ensure, so far as is reasonably practicable, that any plant or supporting structure designed does not present a risk to safety and health, when used for the purpose for which it was designed. For example, the PE must provide a written safety report, to the person tasked with constructing the supporting structure, setting out the methods of excavation work, the hazards associated with the design of the supporting structure and the control measures.
Project manager, project director or project engineer has a duty to use reasonable efforts to ensure that dredging operations comply with the OSHA, the OSHA and the regulations thereunder. This includes taking reasonable steps to ensure that dredging operations have and use the right resources and processes to eliminate or minimize risks arising from dredging operations.
Safety and Health Officer (SHO) must ensure due compliance during dredging work with the provisions of the OSHA and any regulations made thereunder; and promote the safe conduct of such dredging work.
Site Safety Supervisor (SSS) must ensure that the provisions of the AKJ and any regulations made thereunder are complied with; and promote safe working practices particularly during excavation work and generally at construction sites.
Employee have a duty to exercise reasonable care for their own safety and health so that they do not endanger the safety and health of others. Employees must comply with any reasonable instructions and cooperate with reasonable policies or procedures relating to safety and health at work.
1.3 What is needed to manage the risks associated with dredging work
Every employer on a construction project involving excavation work shall ensure that the risks are properly managed by establishing a safe system of work, as required under subsection 15(2)(a) of the OSH Act, concerning the general duties of employers and self-employed persons. Where a construction project involves more than one employer, all employers shall cooperate in establishing a safe system of work to protect their employees and other persons who may be affected by the risks of excavation work.
1.3.1 Creating a safe work system
A safe system of work is a formal procedure that systematically examines a work task to identify all potential hazards that may arise and then describes safe working methods, such as a safe work procedure, that ensure that hazards are eliminated and risks are minimized. A safe system of work is required when hazards cannot be physically eliminated and certain elements of risk still exist.
The five steps to establishing and maintaining a safe system of work are shown in Figure 1. The person responsible for implementing a safe system of work should provide safe methods by:
- (a) considering work preparation and granting of work permits at the commencement of any work;
- (b) ensure clear work sequence planning;
- (c) determine safe working methods and necessary safety measures;
- (d) includes safe access methods and safe escape methods, if relevant; and
- (e) consider tasks such as removal and disposal of building materials at the end of each task.
Figure 1. Risk management process: Five steps to achieving a safe system of work.
Hazard elimination should be a high priority. For example, trenchless technology can replace the need for excavation, except for launch pits and receiving pits; and this can avoid many of the risks associated with open drainage. It also reduces the risks posed by open excavation to the public and traffic.
1.3.2 Safe Work Method Statement (SWMS)
If the excavation work is or involves high-risk construction work, the contractor must prepare a PKKS before the high-risk construction work begins. The PKKS must:
- (a) identify the type of high-risk construction work being carried out;
- (b) determine the safety and health hazards, and risks arising from the work;
- (c) explain how the risk will be controlled;
- (d) explain how control measures will be implemented, monitored and reviewed; and
- (e) developed in consultation with workers and workers' representatives who carry out high-risk construction work.
In certain circumstances, a single PKKS may be prepared to cover more than one high-risk construction work activity carried out at the worksite by the contractor and/or subcontractor. For example, if there is:
- (a) the risk of a person falling more than three metres; and
- (b) trenches with a digging depth of more than 1.5 metres.
In this case, contractors or subcontractors can consult with each other and work together to prepare a single PKKS; or, they can prepare PKKS separately. If they choose to prepare separate PKKS, they must consult with each other to ensure that all PKKS are consistent and do not create additional unplanned risks in the workplace.
1.3.3 Planning your work
One of the important factors to consider at the planning stage is the type of soil to be excavated. Generally, all excavations, except very shallow ones, require support using trench sheeting.
Assessment by the excavation supervisor is essential to review the possibility of any changes in ground conditions and then revise working methods accordingly. Further guidance on general risk management processes can be found in the Guidelines for Hazard Identification, Risk Assessment and Risk Control (HIRARC).
The assessment by the excavation supervisor must be followed by a site investigation carried out (usually by the principal builder) during the planning process, and the following points should be considered:
- (a) underground utilities – including gas, water, sewerage, telecommunications, electricity, chemicals, fuels or refrigerants in pipes or conduits;
- (b) previous use of the site;
- (c) location of existing buildings and new structures;
- (d) results of soil investigations;
- (e) soil pollution;
- (f) water drainage (including underground), water table and soil type;
- (g) location of storage and disposal of dredged material;
- (h) methods of transportation, unloading and disposal routes, amount of working and storage space required;
- (i) the most suitable method for temporary support of excavation walls;
- (j) the number of people involved;
- (k) local weather conditions;
- (l) the dredging period will be left open; and
- (m) adequate emergency arrangements.
The position of all existing underground utility installations, such as sewers, mains (water and gas) and cables (electrical and telecommunications) must be verified before work begins. Pipes or cables should be isolated before work begins.
If excavation work is required to repair mains (water and gas), piped services or cables (electrical or telecommunications) that serve the surrounding population, it is essential that effective communication is established and maintained between the excavation contractor and the neighbouring population throughout all stages of the project. If the work obstructs the main or emergency routes from the building, then egress arrangements must be made.
Once the site investigation and work plan is complete, meetings should be arranged with neighbouring residents so that any special arrangements can be communicated. Ongoing contact with local residents is an important element of the risk control strategy.
1.3.4 Referring your employees
Consultation with workers and safety and health representatives is required in every risk management process. Decisions about construction work and projects are usually made before workers are employed. As such, discussions with workers may not be possible at an early stage. However, it is important to discuss them as excavation work progresses.
1.3.5 Consultation, cooperation and coordination with others who have obligations
Construction sites are often shared with multiple parties, such as civil engineers and contractors. People with overlapping responsibilities should exchange information about the risks associated with the excavation work, including any traffic and plant movements near the excavation area. They should work together in a coordinated manner so that all hazards/risks are eliminated or minimized as far as is reasonably practicable. Consultation should include discussion of:
- (a) the nature and condition of the soil and working environment;
- (b) weather conditions;
- (c) the nature of work and other activities that may affect safety and health;
- (d) static and dynamic loads near the excavation;
- (e) interaction with other crafts;
- (f) site access;
- (g) PKKS;
- (h) management of surrounding vehicle traffic and ground vibration;
- (i) the type of equipment used for dredging work;
- (j) public safety;
- (k) existing utility services and their locations;
- (l) the dredging period will be left open;
- (m) adequate welfare provisions, and
- (n) procedures for dealing with emergencies.
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