Archive for July, 2010

Just been busy – Final Prac, stuff like this:

July 24, 2010

This is an example of what will keep me offline for most of the next three months.

I wanted to explain an event, but the schedule is too crowded for the science lesson.  However, the class needs some training in research and report writing approaches.  I therefore made this one evening:  an exemplar to help develop research skills.  Now I have to write the lesson plans to go with it …

How I found out about the causes of compost fires: A description of research

What is the problem?
The compost heap is very large, with a thick layer of wood-chip mulch over it. One of the students reported smoke coming from the compost heap, and it was so. How can compost catch fire?

What I already knew:
Fire requires a heat source, fuel, and oxygen. I remembered that haystacks can catch fire spontaneously after rain, and that turpentine-soaked rags can catch fire if their container is left in the sun. So, organic matter can start burning without an obvious ignition source.  I know that compost heaps get warm.

Is my memory correct?
I checked my memory online: Search terms “haystack fire cause”; I examined only “.gov” and “.edu” sites, and sensible-looking “.org” sites.
www.bcg.org.au/public_resource_details.php?resource_id=862 has some great pictures, and explains the cause.

Given what I know, can I predict what experts will say?

I think compost probably catches fire the same way – as a gardener, I know that I have to keep my compost quite moist (squeeze hard and a little moisture comes out) for efficient and safe decay. I predict that: part of that is reduction of fire risk.

What do experts say?  Is my prediction correct?
I checked online.  Search engine : Search terms ‘ “compost heap” fire cause’; I again selected .gov, .edu, .org. I checked only two sites of the promising ones, as they agreed:

http://www.uow.edu.au/~mnelson/research.dir/compost.html

It mostly made sense to me, but I didn’t have the time to translate the maths. This example shows why, and has an important point about the microbes involved (I have put that part in bold type):

“We model the heat release rate due to biological activity as a function which exhibits two types of behaviour: over the temperature range 0<= T<= a it is a monotonic increasing function of temperature whereas for T>= a it is a monotone decreasing function of temperature. This function is given by
(1) k(T) = A1exp[-E1/(R*T)]/ (1+A2exp[-E2/(R*T)].
… This formula encapsulates that activation and inactivation processes occur over different temperature ranges. At low temperatures the metabolic activity of the biomass increases with increasing temperature as enzyme activity raises. These processes are governed by the growth parameters A1 and E1. However, for sufficiently high temperatures the essential cell proteins which are heat sensitive start to denature leading to cell death. …
In practice there is not a unique microbe reasonable for heat generation in a compost pile, but rather many different species which thrive over a sequence of overlapping temperature intervals (Kubler, 1987). The temperature varying active biomass concentration temperature is implicitly incorporated into the model through the chosen functionality for the biological heat release rate.”

Is there an explanation I like?  Should I invent one?

A Good Explanation is at http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex10721
(Printed out, attached for class.) This is from Canada, but biology is global.

Conclusion: If you just need the knowledge for your own use, there is no need to rephrase it.