Can't bomb near powerlines?
 

ABC TV Australia reporting on the Bushfire Royal Commission evidence given by an Air attack supervisor this week, say that water bombers like the skycrane, can't fight fires near power lines.

Vic Bushfires Commission hears of diverted waterbombers - ABC News (Australian Broadcasting Corporation)

So how close can water be dropped near high or low voltage powerlines?



Mickjoebill

I would like to know also, I live in the Adelaide hills, and we have a very high bushfire danger with thick gum scrub right up to our property. The house has plastic water piped protection system but the fire in Vic brought to light how many systems melted or were inactive, and how fast and fierce the correct conditions can bring open devistation

Many High voltage powerlines in the area, This is something i hadnt worried bout till now :\

The work they do is so very appreciated, really putting it on the line for those who they dont even know... :D

Was watching the bombers last year on a fire bout 20km away from my place, this wasnt so dense with wires but very amazing to see a mix of 204, 214b, 206's, 350s and a skycrane up close

Complete routine and flying lined up ready to get back onto the blaze, thats fireman kinda stuff true heroism

I would appreciate if anyone knows anything about the above


Thanks Simon

About three weeks ago I was bucketing 20ft from wires. Not a problem.

RH

But, what happens when it rains, isn't that kind of the same as dropping water on them...?

Think they're talking about the risk posed by wires to aircraft rather than the risk of water on wires...

Could be major high tension runs that the AAS is referring to, but normal domestic supplies are all part of the mix that have to be considered when in and out of the smoke. Many are the SWR's that have loomed out of the murk when running in with a load on a long line :ooh:

DSE do have a long standing preferred policy for belly tanks, their stated reasoning being both safety over the "urban interface", plus reduced risk in a wire environment. All contracted aircraft are required to have WSPS, although the cranes and S61's are exempted :hmm:

But then the SAU and its policies have always been a bit of a mystery to outsiders ;)

Agree - we do it here. Just need to practice, practice, practice. Having a crewman in the back who can see the effect of each drop and plan the next one works for us.

If you need a crewman to tell you the effect of your drop and plan the next one!-best you keep practicing. And stay away from a real fire.

From the powerline point of view! I can think of a number of issues.

Whilst rain water and to some degree tap water may not be an issue, water from other sources could contain enough contaminates (possibly even the retardant chemicals) to cause a serious electrical arc onto the ground/vegitation if a large amount is dropped on a live powerline.
Similarly a few tonnes of water dropping on a line could cause structural failure, bringing the line down onto the ground similarly causing arching.

Neither of these would, I think, help in preventing the spread of fire and may even cause secondary ignition of vegitation.

Granny:

What a shame that you have to drag down what was becoming an interesting thread with comments designed to raise the hackles.

All I am saying is that we can bomb with a lot more accuracy with someone in the back.

Plse feel free to contact me PM if you would like to pay us a visit - maybe we could learn from each other instead of making personal attacks.

a long overdue thankyou
 

Last year when the big fires went through Marysville & Labertouche (Vic/Aus) my Brother & nephew were helping a mate defend his property at Labertouche near Drouin just north of the twin BP roadhoses on the Princes Freeway. By the time I got back, all the roads were blocked & I couldn't get through to assist.

Skycrane boys (& many others) were using his large dam as a water source & kept the front at bay or concentrated their efforts saving dwellings, at one point though, the wind swung around & turned on them, & the lorry truck with the makeshift tanker 6 x 1000Lt crate tanks was almost engulfed, were it not for the actions of the skycrane driver who dumped a load right on top of them, there might have been a few more names to add to the statistics of that day.

I thank you sir, for a job well done & assure you that they lads had a beer or two on your behalf that day.

hats off to anyone who any chopper pilot in heli-tak role.

Transcript
 

Here is a transcript of the exchange between commissioner McLeod and DSE manager and air attack supervisor on the 7th, Mr Lawlor.
Page 45 of the transcript of 16th Sept. in general they were discussing the Beechworth fire.
Some context, earlier in the week the commission heard from a scientist who said the Beechworth fire started when an electrical line touched a pole which then sparked. He said the line probably broke when hit by a falling tree.

http://www.royalcommission.vic.gov.au/getdoc/60d94c96-6166-442b-85f7-a0cd2e54b5ce/Transcript_VBRC_Day_052_16-Sep-2009-(1)

It is worth reading all of the evidence from Mr Lawlor as it gives more contex to this exchange.
As far as I am aware it is the most explicit exchange during the commission regarding helicopters near powerlines.

Some say the majority of fires on Feb 7th started near powerlines so the fact that the question was raised by one of the commissioners is an indication that they want to get to the bottom of a helicopters capability at dealing with fires near powerlines.


Mr Lawlors response is prefixed thus ---

COMMISSIONER McLEOD: Could I just suggest, while counsel's proposition was a hypothetical one, could I suggest that had an Erickson been at Beechworth ready to be operational, it could have arrived at that fire as quickly
as the two fire tankers had arrived which, with the load of water, it would have had the advantage of being able to use the water on the fire where there were electrical lines insecure in a way that it wouldn't have been possibly for the attended fire trucks to be able to apply water to the fire when it was in a very small area?
---It wouldn't have dropped on the lines.

COMMISSIONER McLEOD:For what reason?
---Safety reasons, would be my judgment.

COMMISSIONER McLEOD:What would be the safety issue with dropping - doesn't it rain occasionally?
---Aircraft don't operate near wires. They are one of the principal causes of fatalities in aircraft operations.

COMMISSIONER McLEOD:But a helicopter of that size wouldn't be down at electrical pole level?
---It has a very long snorkel that it sucks up, so it would have to drop from a long way up and again you are getting the dissipating effect of the winds, but they don't operate on or above electrical lines while they are dropping water or foam.

COMMISSIONER McLEOD: That surprises me, but anyway, I accept your advice.


Could this exchange be used to characterise helicopter activities around fires that start near power lines as being somewhat limited?

Mickjoebill

Operate near lines all the time---It's not a problem, as long as you know about them:

http://i76.photobucket.com/albums/j3...lawareness.jpg

Generally speaking, the biggest problem with dropping water on energized powerlines is the possibility that the water will act as a conductor between the helicopter and the powerline. I have dropped on (over) powerlines many many times, and it has never been a problem for me, but I have always dropped from a fairly high altitude and made sure that the drop was cut off well before the bottom of the drop reached the lines. Having said that, I know of at least one collegue that has received a jolt from a drop over energized lines.

I have done fires and I work on energized lines, it is impossible to get a jolt in the helicopter. The lines can flash if the water provides a path from the phase to the ground or earth/shield wire to phase but the helicopter is not earthed and is therefore not in danger from the flash-over. If it was, your colleague would not be alive to tell the tale.

For the pilot, the worst case scenario is getting the bucket caught, for the guys on the ground it is the water providing a path for the current to flow which will result in a HUGE bang and a secondary fire. Dense smoke does the same thing as water and can create a flash-over risk.

I understand that high altitude drops were being dispersed by the high winds.
But based on the expert testimony one would think that there is little point in sending a helicopter to a fire that has started near a powerline.

Even if the power line is energised, surely a nearby drop would help containment?



Mickjoebill

In response to Jab, if there were no possibility of a flashover due to there being no ground from the helicopter then why do the powerline repair guys wear a mesh suit and zero out the relative potential between the airframe and the wire before reaching across??

Still a difference in potential exists, not as large as the one to ground but surely enough to flash over?

Any sparkys or electro weenies out there willing to chime in??

Jab, I would assume that if the water column were to stretch from the tank to the ground, with the wires in the middle, I would think that there is definitely a potential for a jolt. That's been my concern anyway.

The colleague I was referring to above informed me that he did not receive a jolt himself, but rather, observed a jolt (flashover) below him after the drop.

PT6ER

There is a potential difference between the helicopter and the conductor or shield wire and may be up to a few thousand volts so the linemen need to be protected, but it is very minor compared to the voltage of the transmission lines which range from around 130 KV up to 765 KV. If you have seen the videos, you will see the arc from the wand to the conductor from around 12 inches depending on the line. The safety distance for phase to ground for an average transmission line of 230 to 242 KV is 5 foot 3 inches, a very different beast from static electricity. A 765 KV line has a minimum approach distance of almost 15 feet and a phase to phase safety distance of 26 feet! Drop a load of water across that line and it is going to be spectacular but it is an unrealistic scenario. For interest, a 765 KV structure is so large that if you try to land on the cross-arm on the top, the skids of a LongRanger are not long enough to fit across the gap between members. It is a very large structure and water drops are normally made from a lower height so dropping from overhead a 765KV line is unlikely to happen.

As the helicopter is, or should be, above the power line, the current will follow the path of least resistance which would be from the line, through the water to the ground leaving the helicopter pilot amazed at the violence of the explosion but otherwise unscathed. If you have thick smoke under the line and add a water drop to that equation, a phase to ground flash-over is a distinct possibility. I have dropped water near lines but have never had the need or desire to drop directly over any and wish to keep it that way.

Jab, thanks for the explanation.