Gas Service Strike During Shaft Drilling
During a 0.9 m diameter, 12 m deep shaft in a commercial lot, the auger penetrates a 100 mm plastic gas service at 2.8 m. The crew hears a hiss and smells gas. The rig is 7 m from a site trailer with a running diesel generator; the wind is blowing from the shaft toward the trailer. The rig operator is in the cab with the engine running; two laborers are at the shaft edge; no one is in the hole. The site is fenced but a public sidewalk is 15 m away. The foreman radios 'pull the auger and move the rig' and walks toward the shaft to look.
1. What are the immediate emergency actions? Why is the foreman's instruction wrong?
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Immediate actions:
- Stop work and sound the alarm. Order everyone away from the shaft and upwind. Do not approach the shaft to look.
- Eliminate ignition sources. Do not start, stop, or operate the rig, generator, vehicles, or electrical switches in the gas area. The rig engine and generator are running ignition sources; evacuating people is more important than shutting them down if approaching them is unsafe.
- Evacuate upwind and account for personnel. Move the crew and the trailer occupants upwind, away from the gas plume, and establish a assembly point. Keep the public off the sidewalk if the plume or evacuation route affects it.
- Call 911 and the gas utility. Give the location, gas service size, and wind direction. Do not use radios or phones near the leak; use them from the safe area.
- Establish an exclusion zone. Keep vehicles and people out until the utility and responders declare the area safe.
The foreman's instruction is wrong because pulling the auger can release more gas and create sparks or static, and moving the rig brings a hot engine and exhaust through the gas cloud. Walking toward the shaft to look exposes the foreman to the leak and may put him in the ignition zone. The correct priority is people away, ignition sources controlled from a safe distance, and emergency services notified.
2. How would you establish the exclusion zone and notifications, and what information must be given to responders?
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Establish the zone from the upwind side, using gas readings if a calibrated meter is available from a safe distance. For a natural gas release, start with a conservative zone of at least 50 m in all directions and expand it based on odor, sound, gas readings, and responder direction. Because the wind is carrying gas toward the trailer, include the trailer and the downwind area. Close the sidewalk and access road as needed. Deny entry to all but emergency responders and utility personnel.
Notifications should include 911, the gas utility, the site owner, the general contractor, and the local authority having jurisdiction. Give responders:
- Exact address and access route.
- Gas service size (100 mm plastic) and depth (2.8 m).
- What was hit and whether flow is still escaping.
- Wind direction and the location of the trailer, generator, and public sidewalk.
- Number of personnel accounted for and any injuries.
- Whether the rig and generator are still running.
Do not re-enter to shut down equipment unless responders or the utility say it is safe. Record the time of the strike and the actions taken.
3. What must happen before work resumes, and what changes should be made to prevent a recurrence?
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Work should not resume until the gas utility has isolated and repaired the service, responders have declared the area safe, and calibrated gas readings show no hazardous accumulation. The excavation and shaft should be inspected for damage, and the gas main should be exposed and protected before drilling restarts. Any ignition sources must be controlled during re-entry and repair.
Prevention changes:
- Obtain a current utility locate and pothole all services within the tolerance zone before drilling. A painted mark is not verification.
- Revise the drill plan to show the service location, depth, and clearance, and relocate the shaft if clearance cannot be maintained.
- Brief the crew on the strike procedure: stop, evacuate upwind, no ignition sources, call 911 and the utility, and do not pull the tool or move the rig.
- Keep the generator and trailer outside the drill exclusion area and establish a designated assembly point.
- Have a gas monitor and a written emergency plan on site.
- Report the strike as required by the site safety plan and the authority having jurisdiction.