High Temperature - Grass Fires

[richlist]

Over the last week there have been a number of reports of serious fires during the heatwave. They start off as grass fires in adjoining fields. What I don't understand is how a grass fire sets a house alight. Can anyone explain how it happens ?

[servodude]

Over the last week there have been a number of reports of serious fires during the heatwave. They start off as grass fires in adjoining fields. What I don't understand is how a grass fire sets a house alight. Can anyone explain how it happens ?

In places where wildfires are expected there is the concept of firebreaks; a managed gap between the burny part and where the humans are; you don't have them in the UK - why would you?

Even then fire travels through/over breaks via embers on the wind

During an event these don't take much encouragement to propagate/start a new blaze because of the hot dry environment
- once your vegetation, which when you think about it is plants with roots that normally are adept at pulling water from the ground, is burning, the jump to burning other stuff is pretty easy

I can remember as a child our neighbour knocking over a charcoal bbq and burning a few acres of gorse on a golf course. This was perhaps '86, just south west of Paisley - and it was fierce taking a few tenders to get under control
- with the right/wrong conditions it would have been much much worse

-sd

[swill453]

Over the last week there have been a number of reports of serious fires during the heatwave. They start off as grass fires in adjoining fields. What I don't understand is how a grass fire sets a house alight. Can anyone explain how it happens ?

Grass fire spreads to wooden fence, which ignites garden shed, then flames lick towards house window frames, or eaves.

Or similar.

Scott.

[DrFfybes]

Gutters full of dried leaves and moss, grass clippings

It isn't the high temperatures as such making things burn (unless you have a very hot compost heap, but I've seen those catch fire before), it is more that they dry everything out so it catches fire much easier if a spark does reach it.

Paul

[richlist]

Yes that all makes sense.
I think my problem with understanding the issue stems from my having a long garden, wire fencing, a wooden shed a long way from my house (which doesn't contain paint, other flammables or gas cylinders) and very little wood in the house construction.

[Dod101]

I have often thought about the timber construction of modern houses compared to old stone houses. Obviously even stone houses have a lot of timber in them but not far from me a modern timber house burned to the ground and it was caused by a heater used on colder evenings. Apparently the heat got onto the soffit boards and they caught fire, quickly engulfing the entire fairly large property. It was quite new so it was quickly reconstructed as the foundations would have been unaffected and no doubt they had all building plans.

Dod

[UncleEbenezer]

It isn't the high temperatures as such making things burn (unless you have a very hot compost heap, but I've seen those catch fire before), it is more that they dry everything out so it catches fire much easier if a spark does reach it.

Paul

This is also a point where litter matters most. Anything that can focus the sunlight to a point in the manner of a lens or mirror has potential, and that is maximised when the sunlight is strong and conditions are dry.

Note that litter here could include things that weren't intended to be permanently discarded. A car left for the day, for instance.