Excavation - Strategies & Effective Practices to Manage and Mitigate Hazards

Effective Practices to Manage and Mitigate Hazards

Defer excavation to a future turnaround or outage

• When the risk of excavation is considered unacceptable, consideration should be made to defer it until the plant is in a safer condition.

Identify all underground utilities and pipelines

• All utilities and lines should be properly identified and appropriate parties notified before beginning any digging or clean-up work.

Prevent spoil falling back into excavation

• Spoil piles should be at least 0.6 m (2 ft.) from the edge of the excavation.

Erecting scaffolding in a safe location

• Scaffold bases should be at least 1.5 times the depth of an excavation away from the edges of the excavation (including trenches).

Protecting hidden pipes and cables

• Mechanical excavators should not be used within 3 m (10 ft.) of any pipes, cables, or other obstructions.

Effect of plant and vehicles

• Do not park plant and vehicles close to the sides of excavations. The extra loadings can make the sides of excavations more likely to collapse.

Preventing excavation collapse

• Heavy equipment should not be operated within 1.8 m (6 ft.) of any excavation.
• Cranes should not be operated closer than the depth of the excavation.

Recognizing hazards

• A qualified person should make daily inspections of excavations using the approved checklist prior to the start of the work shift.

Protecting the excavation

• Guardrails or barricades, as necessary, should be established a safe distance from the excavation to protect individuals and mobile operating equipment above the excavation, or if the excavation is left unattended overnight.

Restricting access to excavation

• No personnel should be permitted in the excavation or trench when power equipment is being used to perform the excavation.

Identifying excavation

• Blinking warning lights should be used at excavations at night where there are personnel or vehicle movement.

Preventing authorized access

• Only authorized personnel should enter the excavation.

Keeping excavations dry

• Ensure there is no water seepage into the excavation

Ensuring safe atmosphere for working

• Qualified personnel should test and monitor the atmosphere while personnel are present (e.g., combustibles, toxic gases, or low O2).

Providing safe egress and access

• Ladders or other means of access should be provided every 7.5 m (25 ft.) in all occupied excavations, extending a minimum of 1 m (3 ft.) above the top of excavation wall.

Preparation for an emergency rescue

• Emergency rescue equipment should be immediately available for excavations considered as confined spaces.

Recognize changes in process conditions

• Excavation permits that extend over many hours should be reevaluated to ensure the surrounding area and plant conditions have not significantly changed, and that the controls detailed on the permit remain valid.

Ensure resources to adequately assess safe work activities

• Time pressures and/or task complexity stresses placed on authorizing personnel to get permits issued can compromise the safety process through the adoption of a “seems OK to proceed” mindset. These situations are associated with a higher frequency of process breakdowns and the introduction of additional risks.
• Specify degree of operator presence, consistent with magnitude of identified hazards.

Use hazardous area classification to prohibit specific activities and specify classification of equipment usage

• Hazardous zoning of the site enables the specification of the type of equipment allowed within each area.
• Only electrical equipment meeting the requirements of the hazardous area classification should be used in those areas.  This can include, but is not limited to intrinsically safe equipment.

Use of ventilation to bring fresh air into excavation

• Make sure excavation is not enclosed.
• Ventilate excavation to ensure hazardous fumes do not collect.

Use of bonding and grounding to ensure that static electricity does not accumulate and cause a spark when disconnecting pipes in an excavation

• Understand what processes and equipment are subject to static electricity.
• Install grounding and bonding cables to applicable equipment.
• Inspect grounding and bonding cables prior to performing excavation.
• Replace grounding and bonding equipment if damaged or compromised.

Continuous monitoring of the environment; stopping work if combustible gas levels are detected

• Gas testing should be carried out by certified gas testers.
• Gas test equipment should be periodically calibrated and tested before use.'
• The authorized gas tester should instruct the work party on the type of continuous gas monitoring (audible alarm preferred) being used and ensure they know how to respond to rising % LEL levels.
• Work should commence no later than 1 hour after the initial gas test is recorded.
• If work is suspended for any period, another gas test should be performed before the excavation permit is reissued and work recommences. 

Clear identification of equipment on the plant

• Ensure that the equipment to be worked on is correctly identified and labelled so that it will be correctly isolated and purged.  

Isolate, depressurize and purge equipment to be worked on as well as other potential nearby combustible fuel sources

• Lock Out / Tag Out should be linked to the permit and a necessary precursor for commencing work.
• Good practice is to demonstrate the equipment is energy- and gas-free before excavation commences.

Use of dedicated worker on standby with communication capability in the event of an emergency

• A dedicated standby person should be part of the work party for any excavation.

Ensure that all workers are competent to execute their responsibilities

• Provide training to all personnel in excavation policies and procedures.
• Ensuring contractors have required craft qualifications.
• Closely supervise all contractors to ensure they are aware of all hazards and how to respond to emergencies.

Ensure excavation equipment is in good condition

• Grounding of electrical equipment should be within the excavation area in case of grounding sparks.

Communication is essential between the control room, the operating personnel, and the people conducting the work

• Communication with the control room at all times is essential.
• If an emergency alarm is sounded, all excavation work must immediately cease.  All gas checks must be repeated before work can recommence following an emergency alarm.