Hey Charles, Thanks for your reply. First off I'd like to suggest that anyone truly interested in Fire Ground Activities and serving their community, should join their local fire department if possible. I'm sure the community would appreciate it and the fire dept. could most likely use the help.
I did read that section of the UL document outlining the test they performed using class A foam as well as much of the other resources you suggested and I do appreciate your advice. I do however have several observations I'd like to explore. But first, I'd like to share a perspective from a rural Volunteer Fire Fighters point of view (who just happens to have been installing PV since 1991). Although each fire is unique, Fire ground activities can generally be broken down into two distinct categories: Initial attack (Scene Size up, Ventilation / Knock down) and Overhaul (clean up).
Initial attack happens very quickly. Ideally within the first half hour or less. Scene Size up (The first step in Initial Attack) usually happens within the first five minutes. During that time the IC (Incident Commander) needs to quickly and accurately determine the scope of involvement and formulate a safe and effective plan based on the circumstances and resources available. Ventilation and fire suppression tactics (Knock Down or Fire Control) go hand in hand. Toxic smoke, heat and even flames can be controlled using ventilation. In some cases, applying water to a fire without proper ventilation can actually exacerbate the situation because water turns to scalding steam and expands rapidly. It's primarily during the ventilation / knock down phase when folks cut hasty holes in roofs and walls and find themselves crawling around in attics and such.. many times in poor visibility or by feel alone. While using foam is not a perfect solution, it's during this Initial Attack / Ventilation phase I propose the use of properly applied foam on a PV array can quickly and effectively help mitigate a potentially lethal situation.. using equipment already familiar to most departments.
Again, I did read through the UL document outlining the tests they conducted using class A foam to reduce Voltage in a PV array. I found it interesting that they conducted the test in less than ideal conditions (approaching darkness and changing weather conditions). They eventually pulled the plug because of these conditions and stated "More research needed to be done". The second chin scratcher for me was that they only tested with a 1% mix (Very wet) and applied only 2-3". While a wet mix is appropriate for extinguishing a wood fire (basically it's a wetting agent at that point), as they noted, it did not stick well to the glass panels. They did say however it did stick better to the laminates and was effective in reducing that output voltage. The more troubling point for me is that they seemed to only apply 2-3" of wet runny foam, watched it run off, gave up and packed out.. and concluded that Class A foam was not effective in significantly reducing voltage in a PV array.
Obviously, if a dept. has the resources (and the proper training) to quickly and safely apply black plastic sheeting to an array during the Initial Attack phase, that should be their first choice. (Assuming it's an older install without rapid shutdown). But if they're anything like our average rural Dept. (where we're lucky to get 6 people to show up), a sticky / dry (5%+) mix applied at least 6-10" thick might be a good temporary option in an emergency situation.. certainly better than no protection at all.
During the mop up phase, yes, a more permanent method of disabling an array may be necessary. I also like to suggest sending a team in with yellow spray paint to identify all DC home runs if possible.
Also I feel worth mentioning here, I was involved with one commercial project where we were required to short all strings and home runs prior to final termination. The logic was that by shorting, it reduced the voltage to zero (Eliminating a potential shock hazard) and made it easier to identify current carrying conductors and connections with a thermal imaging camera.
In conclusion, I could not find in any of these resources any statement the read "Foam should not be used". Agreed, it's not perfect and should not be relied upon, but neither should black plastic or even some connection strategies. Wind can blow tarps around, or they can be torn. Wires can get jostled around and open or make contact. In my view, a thick layer of sticky, heavy / dry foam piled up on an array can be quickly and safely applied by one person (and a pump operator) and can temporarily reduce array voltage in a short term emergency situation.
Certainly if you could refer me to information that suggests this is not the case or is dangerous and "Should not be used", I would appreciate it.
Thank You. db
Foxfire Energy Corp.
Renewable Energy Systems
-------- Original Message --------
Subject: Re: [RE-wrenches] Fire fighters safety class
From: Charles Picard <cpic...@solarcity.com>
Date: Wed, September 21, 2016 9:39 am
To: "d...@foxfire-energy.com" <d...@foxfire-energy.com>
I’ll try to stop short of playing armchair firefighter here, and stick to what legitimate data is available. I follow most of the prominent Firefighter trade rags, and while there is some good technical content, there are also a fair amount of opinion pieces.
The UL study linked earlier is typically the basis for any credible guidance on tactics or strategies, largely because there has been very little research done in the U.S.. In section 9 of that document you’ll find the analysis of the de-energizing experiments conducted. These quotes stand out to me:
1. “It was the consensus of those witnessing this experiment that this Class A foam was generally ineffective in blocking what little illumination the sun was providing that day.”2. “The application of ordinary Class A foam with a compressed air foam system did not prove to be effective or reliable in blocking sun to an array of PV modules.” (Note: VT is likely to have much steeper roofs than used in these tests.)3. “…firefighting foam should not be relied upon to block light.” – Section 14
You bring up a great point about the rank-and-file firefighter needing something quick and effective. Foam may be quick, but we would never say with confidence it is safe and effective. (How does an “average Fire Fighter” confirm that hypothetical 20Vdc?) I’d also ask that we start first by examining the need…Why would the firefighters need to de-energize the array during active fireground operations? Are those scenarios both plausible and likely?
As a practical matter, de-energizing the array itself is going to be most important post-incident. This is admittedly a gap in coverage in this country. “Board-up”, or salvage companies may not be trained to make these systems 100% safe, so each Fire Department is left to seek out a local PV professional to offer guidance.
Another document that may serve as a blueprint for developing standard procedures is here: http://www.nfpa.org/news-and-research/fire-statistics-and-reports/research-reports/for-emergency-responders/fireground-operations/fire-fighter-safety-and-response-for-solar-power-systemsThe bibliography is quite extensive.
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