OT Firemen unable to tackle fire effectively due to solar panels on roof

[Man at B&Q]

*very* sticky foam, preferrably.

MBQ

[Nightjar]

It seems they have - evacuate everybody and try to contain the fire while it burns itself out.

Colin Bignell

[Chris Hogg]

The item came up on our local BBC TV this evening. Apparently it's guidance issued by Devon&Somerset Fire and Rescue Authority, as opposed to an on-the-spot decision by the fire officer in charge. They're worried that the fire crew may be electrocuted when hoses are sprayed onto the panels or exposed wiring. The makers of the solar panels say it can't happen.

[Andy Burns]

I checked the standard operating procedures of a local fire service, their documents for dealing with fires in buildings and fires involving electricity were update a few years ago to take account solar panels.

In short ... make sure all personnel know that solar panels present, they and their wiring may remain live even after isolation (possibly under moonlight, or emergency scene lighting) so don't touch, they might fall or result in broken glass so don't work under them, there's a small risk they might give of nasty fumes so wear breathing apparatus anyway.

Nothing to say avoid tackling the fire because of them.

[dennis]

So what's the big electrical different between the water from the hoses and rain? Solar panels sit in all sorts of weather and nobody gets electrocuted because they are wet.

[polygonum]

Not a lot. But...

Cold water onto hot glass might break it. Water sprayed upwards at high pressure might get to parts rain doesn't reach. Fire might already have damaged the panels. With rain there is no potentially conductive stream of water from a person to the panel.

And probably dozens of other differences.

[tony sayer]

Stunning knowledge of the leccy den;!...

[John Williamson]

They are, of course, willing to conduct the experiment by spraying the water onto an overheated set of their solar panels while holding the brass end? No? I didn't think so...

One important difference is that rain isn't being delivered at high pressure through a hose with a conductive end fitting being held by an earthed fireman. It's also slightly less conductive than most tapwater.

[js.b1]

and specifically HID lighting as I recall.

[js.b1]

1m of water has quite a high resistance.

a) additional external thermal fuses on a per-panel, 85oC or even 63oC trigger would be sufficient to drop out panels.

b) N.O. relay on every panel which disconnects following loss of external 240V power (SELV relay feed supplied from a grid PSU).

Sounds like we might also need thermal fuses on the connection boxes using a system like "b)".

[Dave Liquorice]

How about a solar panel heated to a few hundred degrees from the fire below and sprayed with loads of cold water? Will the glass take that sort of thermal shock or just explode? Then of course is the insulation on the wiring from the live panels, at over 500V DC, able to withstand a fire where it can easily get to over 1000C inside the building?

[dennis]

Stunning lack from you. You just haven't thought about what happens if the fire happens while its raining, but you don't think at all AFAICS.

[harry]

e:

Well if the fire had got that bad, not a lot to save.

[harry]

I think probably more danger from the wiring that the panels.

[harry]

igger would be sufficient to drop out panels.

240V power (SELV relay feed supplied from a grid PSU).

g a system like "b)".

There was a programme on the TV about "Is is possible to get electrocuted by pissing on a live/third rail"?

They did a lot of tests and the answer was no, not really.

[dennis]

I can't see why they wouldn't be prepared to do that.

Well that raises some interesting questions..

First the question about the solar panels...

what potential is going to be between an earthed fire man and a floating DC source? AFAIK there is no low impedance path to earth via the inverter.

What is the resistance of a water jet several feet long compared to all the other paths caused by the water spill also going to earth.

Then there is the design of fire engines...

Isn't it rather poor H&S to design a pump to put water over unknown electrical stuff without making provision to keep the metal bits bonded to a safe potential?

What about the insulation in the protective clothing?

There are lots more questions that can be raised if anyone really wants to know the true hazards, however small.

[Andy Champ]

I think there's a high chance that it will cease to float in the circumstances. Either through damage to something, or because another fireman is playing another hose on another part of the system.

Andy

[tony sayer]

Yes the firemen will get wetter than what they otherwise might do;)..

Still smarting from, the dual RCD issue I see;!..

Theres a lot more to this then what it seems you realise. For one during the night or most of the day in this climate there won't be much power they are producing, the real danger is if the mains gets accidentally connected to them and a current might then be conducted through the water thats being played on the fire.

Course unless thats being pumped from a pond or simpler then that won't be that conductive, suggest you look that up on the IEE site theres a very good article on how conductive clean water isn't.

So where does the rain --connect-- them to;?.

Also what happens in the inverter unit?, how is that or does that actually "connect" the panels to the mains incomer?..

[tony sayer]

So where is the other end of the rain connected to;?..

[polygonum]

For fully detached building with plenty of space around, maybe true.

For a semi, a terraced, one right by several other buildings (typical of cities), then failure to fight that one might have very severe consequences for neighbours. And if any of the neighbours also have solar panels...