With Hawaii Island’s power supply riding on wooden, flammable utility poles, what can be done when they’re threatened by 2,100-degree molten lava?
That’s the question employees at Hawaii Electric Light Co. have been asking themselves as the June 27 lava flow has appeared likely to cross Highway 130 near Pahoa. And on Friday, they constructed as proof of concept two different models for protective structures designed to surround the poles and dissipate the intense heat that would ordinarily cause them to burn and fail.
Following widespread power outages brought on by Tropical Storm Iselle, HELCO has publicly stated in recent weeks its intention to maintain electrical power to communities in lower Puna in the event that the lava flow encroaches on populated areas. Plans for doing so have been broken down into three broad categories, explained HELCO spokeswoman Rhea Lee.
First, the company has been working on extending transmission lines from Makuu Drive along Beach Road into Hawaiian Beaches, providing a secondary route to get electricity into affected areas, should lines be cut further mauka at Highway 130.
“Secondly, we’ve looked at, should the area get cut off from the rest of the grid, how do we continue to serve sections of Puna?” Lee said.
To that end, HELCO has moved a large, 1 megawatt diesel-powered generator into an area near Kapoho to generate enough power to keep the lights on for at least some of the homes that find themselves without power.
And third, the utility has taken a long, hard look at how it can protect its utility lines. One method, which HELCO has discussed in the past few weeks, is to extend the length of the span between utility poles. By using taller, reinforced poles, the company can increase the average distance between poles from 250 feet to a limit of 1,800 feet, she said.
In the event that the lava flow remains narrow, spanning across the lava flow could be a workable solution, Lee said. The wires are seated high enough in the air that any radiant heat given off by the lava on the ground would be dissipated in the air before affecting the lines.
But, if the flow spreads out over a large area as it approaches transmission lines, spanning the lava may not be enough to maintain electricity to lower Puna, and that’s where the idea to shield the poles comes in, Lee said. It’s an idea that HELCO had to largely explore on its own, because as far as anyone there knows, it’s never been tried before.
“The design has gone through many different iterations. It’s something that was developed internally in consultation with experts,” she said.
What the designers learned from lava experts is that a flow doesn’t necessarily create a very strong lateral force, meaning that when it runs into objects, it tends to flow around them like water, rather than pushing strongly against them. If an object is rooted well, like the utility poles are, and it can resist the intense heat of the lava, it has a chance to survive the flow.
The design that HELCO employees believe will work the best is one that begins by wrapping the wooden pole with a blanket-like strip of thermal insulation. Then, a large concrete dry well pipe about 9 feet in diameter and 6 feet tall is placed at the base of the pole, and wire horse fencing is used to create an approximately 15-foot retaining wall around the pole. An excavator is then used to fill up the wall with porous cinder. The bottom of the whole structure is then covered over with a mound of loose cinder to protect the dry well pipe.
The cinder, Lee said, is a poor conductor, and therefore dissipates much of heat from the lava before it can penetrate to the wooden pole.
“This is experimental,” she added. “We don’t know if it will work. But we hope it will.”
The next step will be to test the design and see if it has the desired effect. HELCO will continue to monitor the flow and set up a test of the shields. The devices take about 2.5 hours to build, and use readily available materials.
Email Colin M. Stewart at cstewart@hawaiitribune-herald.com.