Fiber optics install gone BAD.

[itsmoked]

Crews putting in a fiber optic line breached a gas main.

SF Gas fire

Several links on a page

Keith Cress
kcress -

http://www.flaminsystems.com

 

[JAE]

I heard there is a lot of methane on the streets of SF these days.

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[VEBill]

Good old fashioned wooden Telephone Poles have their advantages.

 

[itsmoked]

Not for gas lines.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[oldestguy]

Those "locate services" sometimes make mistakes. This is not an isolated goof.

 

[davidbeach]

Yes, locates are sometimes wrong, but excavation without locates is far too common. Or in the case of a similar type of event in Portland a few years ago the contractor got locates on the south side or the road and then excavated on the north side.

 

[VEBill]

"Good old fashioned wooden Telephone Poles have their advantages."

"Not for gas lines."

When FO was installed (strung along telephone poles) in our neighborhood in 2014, they managed to avoid rupturing the large natural gas pipeline that runs through the area.

So I'd argue that good old fashioned wooden telephone poles have their advantages, especially for any nearby natural gas pipelines.

;-)!!
_{(Just kidding. I know what you meant.}

 

[thebard3]

I heard there is a lot of methane on the streets of SF these days.

I get it.

Brad Waybright

It's all okay as long as it's okay.

 

[Spartan5]

As for the advantages of good ol' fashioned wooden telephone poles...

https://www.ntsb.gov/investigations/AccidentReports/Reports/PAB1302.pdf

On June 7, 2010, at 2:40 p.m.,a truck-mounted power auger (auger truck) operated by C&H Power Line Construction (C&H)struck and punctured a 36-inch-diameter natural gas transmission pipeline operated by Enterprise Products Operating, LLC (Enterprise). C&H, a contractor working for Brazos Electric (Brazos), was using the auger truck to dig holes for the installation of new electric service utility poles. The accident occurred about 45 miles southwest of Fort Worth, Texas, near the town of Cleburne. The natural gas ignited and killed the auger operator and burned six workers, who were transported to a nearby hospital for treatment. The pipeline had a maximum allowable operating pressure (MAOP)3of 1,051 pounds per square inch, gauge (psig) and was operating at 950 psig at the time of the accident. Total property damage and clean-up costs were estimated to be $1,029,000.

The C&H auger operator was preparing to bore a hole for an electric utility pole to be installed near a pipeline right-of-way. Temporary pipeline markers identified the location of what the C&H and Brazos crews believed to be the only underground pipeline, a 36-inch-diameter, high-pressure, natural gas transmission pipeline operated by Energy Transfer (ET). Before digging the hole, a Brazos worker moved the dig location marker to increase the distance between the pole location and the marked underground pipeline to ensure that the power auger would not come close to the pipeline. Unknown to the workers, the new dig marker location was placed directly above a second, unmarked underground natural gas transmission pipeline owned by Enterprise. After the C&H auger operator bored to a depth of about 4 feet, the auger punctured the Enterprise pipeline. The eruption of high-pressure gas threw the 60-ton auger truck more than 100 feet and violently ignited. (See figure 1.) The C&H auger truck operator was killed. Six other workers sustained non-life-threatening burns from the intense fire. The ET natural gas transmission pipeline was not damaged.

That's just one example. Hitting subsurface utilities is a universal hazard.

 

[cranky108]

I still think it is more, amusing among other things, when they hit a brown water line.

 

[ScottyUK]

How does a 36" gas pipeline get missed off the services schedule? Small branch mains I can understand getting missed, but a 36" pipeline??

 

[itsmoked]

Scotty; It's probably one of those things where there are big

signs everywhere and so it's assumed when a USA call is made all the yokels show up to mark the lack of sewer lines and water pipes and maybe no one shows up to mark the 36" transmission line because, well, DUH, there are already signs. Problem is they don't actually say where the line is other than 'near by'. Then if someone digs by hand carefully and finds the line safely they know where it is and proceed to drill their hole. Unfortunately this doesn't work well if there are more transmission lines then one present.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[VEBill]

In general, trenches are much much much much longer than holes. Risk of intersection is thus vastly higher. Obviously. Finding a counterexample doesn't change that.

There would be other factors.

I understand that telephone poles go about 4 feet deep. Who buries pipelines that shallow? Our local NG lateral is (IIRC) about 8-feet deep.

 

[fel3]

VE1BLL…

In the areas I have worked the most (central and southern California), it is very common to see water distribution and natural gas distribution pipelines designed for 3 ft minimum cover (water and gas transmission pipelines are typically deeper). Gravity pipelines, such as sanitary sewers and storm drains, also have this requirement, but in my experience it rarely governs (the need to be below the water and gas mains and the slopes required by hydraulics sends these pipelines deeper). I see this requirement in most of the cities and counties I have worked for, though one city I can think of requires 4 ft minimum cover. I have designed state and federal prison in California and both agencies required 3 ft minimum cover.

Fred

==========
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[BridgeSmith]

"I understand that telephone poles go about 4 feet deep."

Maybe in some places, but not here - utility poles never go less than 8 feet here, since the top 5 feet is subject to frost heaving and therefore ignored for lateral stability.

 

[cranky108]

In many older parts of cities, the old maps were not very good. Wood pipes don't show up with metal detectors, and clay pipes don't either.

Old is a subjective term (30 years is a common failure time of UG electric, 75 to 100 years is likely the limits for water and sewer).

I would guess a 36" gas line would be made of steel, where the new and smaller lines are now made of plastic.

The location of this event I would doubt would have much frost heave, and might be shallow because of past earth quacks, or other ground movement/water table.

Then again a 36" gas line maybe a transmission line, and the transmission company might not have been given notice to locate. That's likely why they place so many marker posts.

 

[Spartan5]

it seems as if two things are being conflated.

The line that was hit in the original post was a 4" distribution line.

The line that was hit by the auger rig boring a hole for the installation of the utility pole was a 36" transmission line with four feet of cover over it. This was the result of multiple breakdowns in communication as explained in detail in the NTSB report here:

https://www.ntsb.gov/investigations/AccidentReports/Reports/PAB1302.pdf

I was on a job site once where a 4" distribution line was clipped by a 4" auger being driven by a horizontal directional drilling rig. This became evident when all of the mud in the annulus was blown back suddenly and sprayed all over the rig with no warning, followed by a continuous roar of natural gas. Fortunately (miraculously?) they got the machine turned off before the fuel-air ratio hit the sweet spot for ignition and it just made a lot of noise before the gas company showed up to kill the flow. I was long gone by that point.

There are pros and cons to installing utilities above or below ground. Utility locates are imperfect in either case.

 

[fel3]

Spartan…

About 15 years ago I did the site civil design for an ethanol production plant. One thing the owner required of the design-build team (and which I thought was a great idea), was to perform a record survey of the new construction, including N, E, & Z for all underground piping, vaults, etc. before burial. They also surveyed building corners and FF, edges of pavement, etc. The prime contractor told me it added about $30k to a $40M project. The final product from the surveyor was a 3D Autocad drawing of everything underground and at ground. The process team did something similar for the above-ground piping.

Fred

==========
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[bacon4life]

Event without frost heaving, 4 feet would be very shallow for a pole any more than 15 feet tall. Although some folks use the 10% plus 2 feet rule for pole setting, most soil conditions require an even deeper embedment depth.