 |
| Dr Carvel, ready to begin. |
Saturday 20th September 2014 was the fourth "Bang goes the Borders" science festival, held at St Mary's School in Melrose, in the Scottish Borders. Each year the festival hosts researchers and scientists from several universities, schools and companies who present a variety of hands-on experiments, workshops and some demonstration experiments. Universities present included Heriot-Watt University (one of the event sponsors), University of Edinburgh, Newcastle University, and Glasgow University. Glasgow Science Centre were there too.
For the first time, a member of the fire research team from Edinburgh (me) was there to do some fiery demonstrations. We've been involved in a few 'public engagement' events in the past, but I've never tried to do fire experiments, outside, in such a way as to be entertaining, interesting, and safe. For this, my first attempt, the weather was very much on my side. There was little in the way of wind and the light rain earlier in the day had ensured that the grass around where I was going to be burning things was nicely damp.
The question I had to address in advance was what sort of fire experiments I could do to engage primary age kids (6-12 years old) and their parents? Having happened upon a quantity of 'Swedish Torches' (logs with cuts in them) in a local garden centre earlier in the summer, I decided to use these as the basis of my presentation:
Question: Logs don't burn by themselves,
so why do they burn by themselves when
all that's been done to them is a few cuts?
The answer involves explaining the relationship between fire, air and heat. In other words, the classic 'fire triangle', although I don't think I used that phrase while explaining things.
With two chunky logs quite happily burning away beside me, I asked the audience if they thought a inch thick stick of wood would burn by itself. Most of the kids said no, and they were right. I tried setting fire to the stick with a blowtorch and it self-extinguished as soon as the burner was removed. What I discovered at that point is that primary age kids think blowtorches are awesome. If I'd just randomly set things on fire with the blowtorch for half an hour, they'd have been happy. Anyway, I had three progressively thinner sticks with me as well. Do they burn by themselves? Most of the audience thought the two thinner sticks would burn in isolation. They were wrong. So why does a chunky log burn, but a thin stick doesn't? With a bit of hinting, the kids guessed that the answer was something to do with heat. Result.
Now to wow them with the effects of airflow on a fire. Spinning a small pool of heptane on a turntable has little effect on the burning behaviour, but put a wire mesh around it and spin, and you get a fire tornado. Simple and effective. There were literally gasps of excitement from the younger members of the audience.
Now, having explained the influences variations in airflow and heat flow can have on a fire's burning behaviour, we were ready for the big fire test of the day. I had two identical wooden cribs (a regular arrangement of wooden sticks), about 20cm x 20cm square and about 15cm high. One was going to be burning outside, the other was placed inside a 40cm x 40cm x 40cm wooden box; the lower half of the front of the box was open. I ignited both with the blowtorch and got them to about the same stage of burning. We were going to have a race.
I ran the demos three times during the day and each time about half of the audience thought the 'outside crib' was going to grow faster, while the other half thought the 'inside crib' was going to win the race.
Each time we ran the race, the outside crib showed early promise, clearly being the bigger fire after about three minutes, due to a plentiful supply of air. Meanwhile the inside crib was growing at a slower rate, due to restricted airflow, but retaining its heat for future use. After about five minutes of burning, the inside crib grew rapidly in size and clearly overtook the outside crib in terms of fire size. Then the box went to flashover and decisively won the race.
(Following flashover, the back of the box fell off, venting and cooling the fire; this was intentional and made the fire much easier to extinguish after the experiment...)
These fires were watched by a good number of interested and well behaved kids; perhaps the fire safety engineers or fire scientists of the future! I hope they learned something. Certainly they were entertained.
The greatest feedback I had on the day was from a boy of about 8 years old who shouted across the field at me towards the end of the day:
With two chunky logs quite happily burning away beside me, I asked the audience if they thought a inch thick stick of wood would burn by itself. Most of the kids said no, and they were right. I tried setting fire to the stick with a blowtorch and it self-extinguished as soon as the burner was removed. What I discovered at that point is that primary age kids think blowtorches are awesome. If I'd just randomly set things on fire with the blowtorch for half an hour, they'd have been happy. Anyway, I had three progressively thinner sticks with me as well. Do they burn by themselves? Most of the audience thought the two thinner sticks would burn in isolation. They were wrong. So why does a chunky log burn, but a thin stick doesn't? With a bit of hinting, the kids guessed that the answer was something to do with heat. Result.
Now, having explained the influences variations in airflow and heat flow can have on a fire's burning behaviour, we were ready for the big fire test of the day. I had two identical wooden cribs (a regular arrangement of wooden sticks), about 20cm x 20cm square and about 15cm high. One was going to be burning outside, the other was placed inside a 40cm x 40cm x 40cm wooden box; the lower half of the front of the box was open. I ignited both with the blowtorch and got them to about the same stage of burning. We were going to have a race.
I ran the demos three times during the day and each time about half of the audience thought the 'outside crib' was going to grow faster, while the other half thought the 'inside crib' was going to win the race.
Each time we ran the race, the outside crib showed early promise, clearly being the bigger fire after about three minutes, due to a plentiful supply of air. Meanwhile the inside crib was growing at a slower rate, due to restricted airflow, but retaining its heat for future use. After about five minutes of burning, the inside crib grew rapidly in size and clearly overtook the outside crib in terms of fire size. Then the box went to flashover and decisively won the race.
(Following flashover, the back of the box fell off, venting and cooling the fire; this was intentional and made the fire much easier to extinguish after the experiment...)
These fires were watched by a good number of interested and well behaved kids; perhaps the fire safety engineers or fire scientists of the future! I hope they learned something. Certainly they were entertained.
The greatest feedback I had on the day was from a boy of about 8 years old who shouted across the field at me towards the end of the day:
"Hey mister! Great show this morning! I'll come back again next year..."I think I might go again next year. I wonder what different tests I can do?
Brilliant, Ricky! I wish I could have attended.
ReplyDeleteI love the "for future use" comment, I think I will quote you.
note: for next year, my proposal is to show how to ignite a fire using friction (via smouldering) and how to suppress it (water on fuel, not water on flame).