OHS Code Explanation Guide

Published Date: July 01, 2009
Bookmark this page

Part 32 Excavating and Tunnelling

Section 448 Exposing buried facilities

Subsection 448(1)

The “hand expose zone” is the zone lying within 1 metre of each side of the locate marks that identify the location of the buried facility. Before allowing mechanical excavation equipment to be used within this zone, the employer must ensure that the buried facility is exposed to sight by hand digging, a non-destructive technique acceptable to the owner of the buried facility, or an equivalent method. New water-jet or hydrovac excavation systems for example, can quickly remove soil and under the right operating conditions, do so without damaging buried facilities.

Because of the potential for damage, particularly in the case of water jets cutting through or damaging electrical cables, any non-destructive technique used as an alternative to hand digging must be acceptable to the owner of the buried facility. The employer is responsible for checking with the owner.

Manitoba Hydro has determined that water-jet excavation systems are capable of damaging almost any type of electrical cable, especially 5 kilovolt to 15 kilovolt cables installed prior to 1974. The most susceptible cables cannot be exposed while energized and can be damaged at extremely low water pressures. If the water stream is applied directly to these types of cables, damage can be expected.

Some water-jet excavation systems can reach temperatures approaching 66° C (150° F) and pressures approaching 20.6 kilopascals (3000 pounds/square inch). As good practice, it is recommended that when excavating within 1 metre of any energized or de-energized cable, the water temperature should be limited to 38° C (100° F) and the pressure limited to 10.3 kilopascals (1500 pounds/square inch). The water-jet excavation system should allow workers using it to monitor both temperature and pressure to ensure that the limits are not exceeded.

Wand tips should be of the oscillating type to prevent the release of a concentrated water stream. This type of tip can be identified by the circular pattern created by the water leaving the wand when pressure is first applied to the wand. Tests performed by Manitoba Hydro showed that cables could be damaged when a single stream nozzle end was directed toward a specific location on the cable. Damage was also observed when the single stream nozzle end was used in a sweeping motion.

The damage to a cable created by excessive water pressure appears as a slice of unknown depth, or the outer surface looks as though it has been torn and pulled outward. Cable damaged by excessive water pressure can fail immediately or at a later time as moisture penetrates broken sheathing. Before backfilling, all cables exposed by water-jet excavation should be inspected for damage.

Hand digging requires the use of hand tools. Hand tools are defined in the OHS Code as hand held equipment that depends on the energy of the worker for its direct effect and it does not have a pneumatic, hydraulic, electrical or chemical energy source for its operation.

Subsection 448(2)

Hand digging to expose buried facilities is an important safe work practice that protects workers from potential injury and reduces the likelihood of facilities being damaged. However, hand digging to expose buried facilities that are no longer in use can be avoided if the employer ensures that the planned work does not present a hazard to workers and the employer has the written approval of the facility owner to remove the facility.

Written approval is necessary because the owner may have important knowledge about the facility. For example, a hydrocarbon or gas pipeline could still contain explosive hydrocarbon residue or quantities of a chemical. “Dead” gas mains may contain residual natural gas concentrations in the 5-15 percent range – this is the explosive range for natural gas – making it potentially more hazardous than a live or operating line. Hand digging would still be required in such instances.

An electrical cable or conduit can be mechanically excavated only if it is grounded and isolated so that its disconnection is visible.

Subsection 448(3)

If a high-pressure pipeline (operating pressure of 700 kilopascals or more) falls within the scope of the Pipeline Act, then a mandatory 5 metre hand expose zone must be maintained. If the Pipeline Act does not apply to the high-pressure pipeline, then the pipeline may be treated like any other buried facility and the 1 metre on each side of the buried facility hand expose zone requirements apply. If the employer plans to reduce the hand expose zone to the 1 metre limit, the employer must get the written approval of the owner of the high-pressure pipeline to do so.

Subsection 448(4)

Even if the planned disturbance lies more than 30 metres away from a buried facility, the operator or licensee of a pipeline right-of-way must be contacted if the disturbance is to take place within that pipeline right-of-way. The owner or licensee’s approval must be obtained before any ground disturbance begins.

Subsection 448(5)

Where the use of mechanical equipment is required to excavate within 600 millimetres (24 inches) of a buried pipeline, the activity can only be undertaken under the direct supervision of an owner’s representative. The owner’s representative is the person most knowledgeable about the characteristics of the buried pipeline. This knowledge will help to ensure that workers and the pipeline are protected from injury or damage. Whenever possible, powered excavation equipment should be operated to dig parallel to the direction of the buried pipeline.

Subsection 448(5.1)

This subsection establishes an acceptable option for situations involving emergency work.

Subsection 448(6)

Once a buried facility is exposed, the employer is responsible for making sure the facility is protected and supported so that workers are not injured.

Subsection 448(7)

Once a pipeline is exposed, the operator or licensee must be notified before the excavation is backfilled. This notification provides the operator or licensee with an opportunity to examine the exposed pipeline and to ensure that appropriate protective measures are taken before backfilling proceeds. The operator or licensee also has the opportunity to oversee the backfilling operation.