WorkSafe Bulletin

Underground Distribution Cable Vaults: Guidance for Employers on Risk AssessmentEntering an underground distribution cable vault can put workers at risk of injury from a wide range of hazards. Some of these hazards include the following:

• Electric shock hazards (for example, water, faulty cable splices, or damaged cable insulation)

• Confined space hazards• Asbestos exposure• Atmospheric hazards (from by-products of

cable faults)

Before workers enter a cable vault to carry out maintenance or inspections, employers must identify the hazards, assess the risks, and implement controls to ensure workers' safety.

This document provides guidance for employers on key elements of the risk assessment process for cable vault entry. The scope of this document is limited to cable vaults that contain electrical equipment and to inspection work required before and upon entering such vaults. This document is not a confined space entry procedure; however, it may be used together with a written confined space entry procedure.

About the risk assessment processAs an employer, you should implement and maintain a risk assessment process as part of your cable vault entry program. The risk assessment process should cover the following areas:

• Hazard identification and elimination of hazards

• Risk analysis of the remaining hazards

• Risk evaluation

WS 2017-04 WorkSafeBC Prevention Information Line: 604.276.3100 or toll-free 1.888.621.SAFE (7233)

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What is an underground distribution cable vault?

An underground distribution cable vault is an opening in an underground duct system that houses cables, cable splices, and other electrical equipment. The opening is large enough for a worker to enter on a ladder and is often called a manhole.

Hazard identification and elimination of hazardsAn effective planning process can anticipate hazards in a cable vault before work begins. De-energization of the electrical equipment must be considered as the first step in planning the work. If de-energization is not feasible, then you can use the following guidelines to identify the hazards.

Hazard identification starts with collecting information that could be useful before starting work. This information includes schematics, blueprints, and any hazard surveys prepared previously. The owner of the power system should be able to provide this data. Consider prior experience from previous entries and knowledge from workers familiar with the cable vault.

Energy hazards are sources of energy that can be harmful if workers come into contact with them. Energy hazards could convert to physical hazards (such as heat, light, noise, or gases) through their interaction with materials used in a product or process.

It’s not always possible to have accurate knowledge of all cable circuits within a cable vault. For this reason,

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before entering a cable vault, a qualified worker should contact the owner of the power system and arrange for a Live Line Permit (LLP) or an equivalent form of protection on all the known circuits located in the cable vault.

A qualified worker who is in charge should assemble the crew and conduct a briefing before work begins. The briefing should cover the hazards associated with cable vault work, the procedures involved, special precautions, the means to control the energy source, and personal protective equipment requirements.

The initial entry should be performed by a qualified electrical worker who performs a hands-off safety inspection within the cable vault. This inspection should include the following actions:

• Look and listen for any visible or audible tracking, arcing, etc.

• Note the location and state of cable covers, cable supports, etc.

• Check for leaking, swelling, or collapsed splices.

• Check for proper grounding within the cable vault.

• Check that all circuits have been included in the cable vault permit process.

• Check for vandalism, such as neutral harvesting.

• Perform temperature measurements on all splices and connections. Verify if they are within the allowable temperatures provided by the power system owner or known data references. Temperature readings should be taken again prior to work, and then repeated at a minimum of every four hours.

• Record temperatures on the tailboard form. If temperatures are:

• Within normal limits, repeat testing every four hours

• Higher than normal but below the maximum allowable, repeat testing every 20 minutes

• Above maximum allowable limits, stop work and vacate the space

It’s critical to inspect all high-voltage connectors, such as straight splices, T-body splices, insulated connectors, and transition splices. Check the cable

grounding and halo integrity of the vault.

For submerged energized cables, perform a thermal test every 20 minutes for 1 hour regardless of the initial temperature reading. Then test as per normal and above-normal limits. Water-cooling conditions can lead to a delayed rise in cable temperature.

Risk analysis of the remaining hazardsQualitative risk analysis may be performed by a qualified worker with the appropriate skills, knowledge, and experience to provide an informed judgment without extensive quantitative analysis. Once the risk analysis is complete, verify the controls put in place to ensure that they provide the expected degree of risk reduction.

The following factors may affect the level of risk determined by a risk analysis:

• Source of the electrical energy (for example, BC Hydro, an independent power producer, or a point of isolation)

• Type of current (AC or DC)

• Voltage and normal loading of the energy source

• Fault current-delivering capability of the energy source

• Potential for an arc flash event

• Hazardous live parts

• Parts that have become live under fault conditions, especially as a result of an insulation failure

• Insulation not suitable for the conditions of use

• Effects of arc flash (for example, projection of molten particles)

• Effects from short-circuits and overloads on cable splices and cable insulation

Electrical qualifications

For definitions of a "qualified worker" and a "qualified electrical worker," see OHS Guideline G19.1-2. Follow the link in the "For more information" section at the end of this bulletin.

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• Cable circuit loading due to switching conditions

• Damage resulting from climbing or stepping on cables or cable hangers

• Tools and materials lowered into the vault opening from above

• Ducts, rods, and worker position

• Damage resulting from spiking the wrong cable before starting work

• Secondary effects (resulting from electric shock, slipping, tripping, etc.) that cause workers to fall or drop objects

• Repair work that is due or has not been completed on the circuits inside the cable vault

Risk evaluationRisk evaluation is the last stage of a risk assessment. The goal of a risk evaluation is to determine whether a tolerable level of risk has been achieved. Risk evaluation aids in making decisions about whether a work activity can be undertaken within the expected degree of risk reduction.

As an employer, you should develop a qualitative risk-scoring tool to rank the different hazards according to their risk of injury to workers. The

completed rankings allow you to evaluate the results and prioritize rescue plans.

Factors that could negatively influence risk evaluation include the following:

• Work overload (for example, projects that cannot be managed with available resources)

• Work complexity (i.e., projects that go beyond existing skill sets)

• Excessive work pace and/or duration (for example, unrealistic timelines)

• Inappropriate shift work design (overtime, extended hours, shift rotation factors, etc.)

• Inadequate materials resource management (equipment, supplies, etc.)

• Poor design of the equipment, the cable vault, etc.

• Inadequate training and instruction

For more informationOccupational Health and Safety Regulation

• Section 4.13, Risk Assessment

• Part 19, Electrical Safety

Occupational Health and Safety Guidelines

• Guideline G19.1-2, Electrical Qualifications