I suppose it's similar position to the petrol regulations (https://www.hse.gov.uk/fireandexplosion/petrol-storage-club-association.htm) - it's seems you can only (easily) store 30 litres "at home" (e.g. in a garage in cans) but a couple of cars could easily hold three times that.

   - Andy.

Hi Andy, 

The new guidelines advise domestic Battery Energy Storage Systems to be installed outside if possible but if within a garage or outbuilding the conditions mentioned must be met. In addition if an EV is kept in the same space it's kWh value is counted in ie. added to the value of BESS units and the total must not exceed 80 or 40 kWh (depending on the garage/outbuilding being attached or detached from the domicile.

Regarding the example of my neighbour, obviously with the storage capacity of his two EV's he could not have any separate BESS installed within the garage space, but should anyone have EV's with +40/80 kWh capacity kept in the same space (the PAS is not a Regulation and will be revised in 2 years time). 

Is that somehow worse than parking internal combustion engine vehicles in a garage, given that only 1 litre of diesel holds about 10kWh?

the difference, and it is a biggy, is that we have many centuries of experience with hydrocarbon fires and in all cases, either cooling or removing oxygen quenches the fire and stops the production of heat and we know we can be confident that once extinguished, the fire stays out.

The problem with a battery fire is that when the battery is charged, it provides its own source of (resistive) heating and re-ignition, making it far harder to put out, and once out there is a significant risk of re-ignition.

Mechanical damage to the battery that allows the plates to move and then touch inside leaves it in a 'could trigger at any moment' state which is hard to make safe until is has been made flat, slowly and safely.

In a great many cases it is not just the energy that needs to be compared - consider if you like that a small stick of dynamite, and a mars bar - both store about the same chemical energy and release one megajoule when oxidised fully , but the nature and rate of the energy release makes them the solution to quite different problems.

Mike.

In addition to the above, I wonder if some of the thinking is that the certification process of a car considers management of fire risks in the the systems design of the vehicle. Not to say this isn't covered by the regs for e.g. solar PV installations (I'll admit I don't know, what does the team think?) but maybe not to the same level of detail or policing? On the other hand it could be pure pragmatism that trying to ban people from keeping their cars in their garages is not going to go anywhere, but that doesn't mean that we want to make the situation even worse...

My personal bomb (my wife's petrol hybrid car, with its charger, parked right next to my diesel car) is tidily in the driveway at a safe distance from the house. But that's pure chance.

There a an odd schizophrenia with risks - On one hand cars, with enough fuel in to put the driver in orbit are seen as mostly safe, and are parked almost willy nilly and driven at speed over rough ground, and stairs without handrails that allow folk  to fall and injure themselves are common, even in new build, but on the other hand fixed gas appliances are regulated heavily,  (but not camping gas) and part P does a half cock version of the same thing for fixed wiring, but anyone can plug in an extension lead without training.  

The degree of regulation  is often as much about how easy it is to inspect and control something as the wisdom of bothering to do so.

Meanwhile, large batteries are a reasonably novel risk, and it is fair to say that the public, and fire brigades, are learning on the hoof and in the meantime, anything that publicizes best practice and informs new designs, without scaremongering is to be welcomed.

Mike.

Phased said:

As EV's are battery storage systems, how does this stack up when there are two vehicles with a total of 140 kwh of storage in the same garage?

A fair question ... Other countries have also selected, through some of their national standards, to consider similar limits.

The debate on this is not short.

Phased said:

A neighbour of mine has such in an integral garage with a questionable 1 hour fire rated separation from their timber framed house. 

Depending what happens in the battery fire ... which in turn depends on the specific batteries involved. Some lithium batteries (but not all) might exhibit jet-like flames which get through the 1 hour fire separation in 10 minutes.

Given the house is wooden framed, what does the insurer recommend (or what will they accept) would perhaps be a more pertinent point?

Phased said:

As EV's are battery storage systems, how does this stack up when there are two vehicles with a total of 140 kwh of storage in the same garage?

Why stop at two, electric or hydrocarbon?

Apart from getting planning consent, there appears to be no limit on the capacity of one's motorhouse.