Thread: First Fire of the Season

Back late from listening to a lecture in town on Cosmology. Yes, haystacks can self ignite as noted above. Basically bacterial action, and hay being a very good heat insulator, the heat generated by the bacteria can raise the temperature enough to start a runaway chemical process that changes into actual burning as it gets close enough to the surface to have enough oxygen to actually burn. The secret is to let the hay get dry enough before baling it. You'd think that with the drought that would be easy enough, but I suspect that farmers have thought it was so dry it couldn't be a problem, but the hay being still a bit green, it was. Problem is if you let it get too dry, it breaks up when you try and bale it.

John

Originally Posted by Blknight.aus

the cotton and linseed oil thing I knew about but always assmed that it was a warning as most of the fires I know of involving those had other initiators and that just provided a dandy accelerant and cinder material.


I also knew that mulch piles got hot but they;re also fairly wet and was under the impression that the moisture content would be enough to stop it from flaming up.

This is the process Dave

A hay explosion occurs as a result of the following situation. Hay is stored at a relative humidity above 75% (all relative humidity figures in this article refer to the relative humidity inside the stack, not the relative humidity of the air outside the haystack). This initiates microbial action. This microbial action produces heat which raises the temperature of the stack to 76 C. If the relative humidity in the middle of the stack is below 95% then the microorganisms become inactive and the temperature of the stack drops. If the relative humidity in the middle of the stack is above 97% then the resultant heat of vaporisation of the water dissipates the heat rapidly and the temperature of the stack drops. This explains why very wet silage does not explode. However if the narrow window of 95%-97% relative humidity is obtained then the microorganisms continue to produce heat, which cannot escape, which raises the temperature. This temperature rise accelerates the chemical oxidation of the hay releasing more heat. An ever increasing rate of temperature rise is obtained, i.e. bang - one haystack fire. It is indeed an unfortunate fact that the microbial tolerance of temperature and the start of the chemical oxidation of hay overlap at around 76 C when the relative humidity is 95%-97%. A small window of opportunity (see figure 1) but one which never-the-less can occur.

This is from this article/site http://www.bioline.org.br/request?au97017

very cool... urmmm you know what i mean

Just spent pretty much the whole day with the RFS. Decent MVA rollover this morning on New England Hwy then large bushfire on Waterfall Way this afternoon. Got back at half eleven tonight. Can't believe how dry it is!

Rookie driver still managed to bog the truck though...


Headfire in trees, properties to left of Tanker (Pumper in attendance for property protection) and a last minute backburn in foreground conducted by Tanker crew

Originally Posted by Roverray

.........A small window of opportunity (see figure 1) but one which never-the-less can occur.

.....

It is actually much more likely to occur than it would seem from a first reading - the relative humidity through the bale of hay is likely to vary all over the place, and if it gets as high as 95% anywhere in the bale then the chances of fire become very high provided the hay in question is in a large enough and tight enough body to retain heat (heat not escaping as fast as it is generated) - in other words, a large bale very tightly packed, or more commonly a hay stack. This is why the hay is commonly left lying after being cut and before being baled, and why bales themselves are also often left in the paddock before being stacked.

If you are making silage, on the other hand, it becomes essential to ensure that humidity is above 97% almost everywhere in the bale and/or oxygen strictly excluded to prevent combustion.

John

What is the difference between "hay" and "silage"? On the open downs country in Western Queensland, Tambo-Blackall-Barcaldine-Muttaburra-Longreach-Winton, years ago, there was a practice of laying down stores of "native hay" in "silage pits" and covering with the earth removed to make the pit. This could be stored for many years against the inevitable major drought. I haven't heard of the practice for years and do not know if graziers still do this.

Originally Posted by Brian Hjelm

What is the difference between "hay" and "silage"? On the open downs country in Western Queensland, Tambo-Blackall-Barcaldine-Muttaburra-Longreach-Winton, years ago, there was a practice of laying down stores of "native hay" in "silage pits" and covering with the earth removed to make the pit. This could be stored for many years against the inevitable major drought. I haven't heard of the practice for years and do not know if graziers still do this.

Silage is basically fermented hay. It is stored wet and cut off from oxygen (or it will spoil or catch fire).

My next door neighbour has been feeding his stock for the last year from two large silage pits just outside my fence (now empty, drought still going), so at least in some places it is still an active practice. Not too sure how old the pits were, I don't remember them being filled, but I've been away often enough that it could have been done within the last few years while I was away.

John

Originally Posted by JDNSW

Silage is basically fermented hay. It is stored wet and cut off from oxygen (or it will spoil or catch fire).

My next door neighbour has been feeding his stock for the last year from two large silage pits just outside my fence (now empty, drought still going), so at least in some places it is still an active practice. Not too sure how old the pits were, I don't remember them being filled, but I've been away often enough that it could have been done within the last few years while I was away.

John

Ah, hay is cabbage, and silage is sauerkraut?