Tag: fire triangle

Burning is when you are burning something with fire …

Iconic chemical triangles

Keith S. Taber

Derek was a participant in the Understanding Science Project. When I interviewed Derek soon after the start of his secondary schooling, he told me he liked science, and was currently studying 'burning'.

So, I asked him what that was:

What is burning?

[pause, c.2s]

When [pause, c.2s] a fuel, oxygen and heat gets – in, erm, I'm not quite sure how to explain, but it's like – you get the triangle of fire, and then, burning is just when you've got fire and you're burning something with it.

Okay, so you'd recognise it if you saw it, would you?

Yeah.

Yeah, but maybe it's not that easy to explain?

Yeah.

The notion that 'burning is just when you've got fire and you're burning something with it' – might be considered tautological:

  • burning is when you are burning something

Scientists look to explain natural phenomena with theories, principles, models, and so forth. But for most people, phenomena that they have been familiar with since very young (such as a dropped object falling) do not seem to need explanation – as they are seen as just natural events (Watts & Taber, 1996).

Derek knew about the fire triangle, but his response reminded me of another triangle that is often referred to by science educators.

Johnstone's triangle

For many years Prof. Alex Johnstone (1930-2017) worked at the Centre for Science Education that he founded at the University of Glasgow; where he undertook, supervised, and collaborated on, a good many projects in science education – especially, but not only, relating to the teaching and learning of chemistry and physics in higher education.

However, one of Johnstone's most influential publications must be the short article he published in the School Science Review (Johnstone, 1982) – the secondary science journal of the Association for Science Education. In this short piece he argued that in each of biology, chemistry, and physics, learning difficulties in part derived from how the subject was taught at several 'levels' at once, asking young learners to think simultaneously on different planes as it were. In each of these science subjects, this could be represented by a triangle. In many lessons students would be asked to think about, and inter-relate, considerations from the viewpoints of several vertices.

Johnston's chemistry triangle distinguished between three levels:

  • the macroscopic (the scale at which people observe and handle materials);
  • the submicroscopic (molecular) scale at which many chemical explanations are developed;
  • the symbolic level – where abstract symbols are used to represent the chemistry

"Those of us who are academic chemists can view our subject on at least three levels.

There is the level at which which we can see and handle materials, and describe their properties in terms of density, flammability, colour and so on. We are also interested in the possibility of conversion of one material into another with consequent changes in properties.

A second level is the representational one in which we try to represent chemical substances by formulae and their changes by equations. This is part of the sophisticated language of the subject.

The third level is atomic and molecular, a level at which we attempt to explain why chemical substances behave the way they do. We invoke atoms, molecules, ions, structures, isomers, polymers etc to give us a mental picture by which to direct our thinking and rationalize the descriptive level mentioned above.

These levels could be called (a) descriptive and functional, (b) representational, (c) explanatory. Trained chemists jump freely from level to level in a series of mental gymnastics. It is eventually very hard to separate these levels."

Johnstone, 1982 (added emphasis)

Over the years there have been many attempts to apply, elaborate, and refine Johnston's triangle, and it has been an idea that has proved very productive in thinking about learning difficulties in the subject.

"Chemistry seeks to provide qualitative and quantitative explanations for the observed behaviour of elements and their compounds. Doing so involves making use of three types of representation: the macro (the empirical properties of substances); the sub-micro (the natures of the entities giving rise to those properties); and the symbolic (the number of entities involved in any changes that take place). Although understanding this triplet relationship is a key aspect of chemical education, there is considerable evidence that students find great difficulty in achieving mastery of the ideas involved…" (Publisher's description)

One well-respected, edited, scholarly book ('Multiple Representations in Chemical Education' – Gilbert & Treagust, 2009) consisted of contributions exploring implications of the idea. Indeed, now, there is even a book entitled 'The Johnstone Triangle' (Reid, 2021) with the telling subtitle: 'the key to understanding chemistry'!

Johnstone's triangle is now the subject of a book

Reconceptualisation

Derek was just being introduced to burning as a science topic, and for him it was still just a familiar phenomenon rather than a theoretical construct. We have all seen fires, and can recognise when something is burning – but how many people really know what fire is?1 Burning and fire are everyday concepts – fire is an impressive phenomenon to a young child: one that is salient enough to be noticed. The child's brain then recognises different instances of fire as being similar and it abstracts a spontaneous concept – that there is a category of events in the world that appear like this.

Of course, the brain of the young child does this without using language (it forms a category of events in the sense that it readily recognises new instances – it does not yet have access to have technical notions of 'category', 'concept', 'abstraction' of course.) And the child does not instinctively know this is called 'fire' or 'el incendio' or 'l' incendie' or whatever, until someone who is a more mature member of the child's natural language community shares this label.2

School science will involve learning that there is a formal scientific concept3 called 'combustion' that is basically the chemist's name for burning. However, 'combustion' is a technical term, so combustion will be defined in terms of other concepts. So, whereas in everyday life we recognise what counts as a fire or burning using the brain's inherent pattern-recognition mechanism (a spontaneous conception), in chemistry we have a technical definition (a scientific concept defined in relation to to other scientific concepts, and so 'theoretical').

That is, in everyday life, if you told someone you saw something on fire, it is unlikely anyone (leaving aside science teachers) would ask you which criteria you used to know this: you did not deliberate on the matter, you simply saw, and instantly recognised, a fire. When you refer to a fire, the other person recognises what you mean because they have learnt 'fire' to be the label for their own spontaneously formed conception that allows their perceptual-cognitive system to instantly recognise a fire.

But, for a chemist, combustion is one class of chemical reaction (so the learner can only understand combustion in chemical terms if they have an appreciation of what a chemical reaction is), which only makes sense to someone who has reasonable idea what a scientist means by a substance, as chemical reactions are changes resulting in different substances. Here we have shifted from everyday notions to the theoretical descriptions of science.

In school chemistry, everyday phenomena (e.g., burning) are reconsolidated in terms of technical concepts and language (e.g., combustion). (From Taber, 2013)

The invisible nanoscopic world

But chemists are seldom satisfied with macroscopic accounts – even when posed in technical language. Rather, students will be taught to explain the observable macroscopic phenomena in terms of invisible entities which have unfamiliar properties. Imagined entities such as molecules4, nanoscopic systems which are best understood as fuzzy balls of fields – that have no actual surface, and are mostly tenuous 'clouds' of charge. (Molecules are sometimes modelled as if billiard balls, or sets of balls connected by sticks, but this is just an attempt to represent entities quite unlike the familiar referents available to learners in ways they can make sense of.)

That is, combustion will be explained as a rearrangement of electrons and atomic cores that changes one set of molecules (of the reactants in the reaction) into another (the products). This process will involve energy changes, due to differences in stability of different sets of molecules, and will progress through the breaking and making of chemical bonds.

If the learner is able to form a mental image of (i.e., imagine) chemical reactions at the nanoscopic level, and see how this can be used to explain an actual observable phenomenon (such as a fire), they then also have to learn how chemists often represent these ideas in what is in effect a specialist language – involving chemical formulae, and reaction equations, and the like.

So, when Derek was using a Bunsen burner to set fire to pasta and (not quite set fire to) raisins as he reported to me, he was using a chemical reaction that might be summarised by the chemist or science teacher as:

CH4 + 2O2 ➞ CO2 + 2H2O

Johnstone suggested that the symbolic representation was the third level, alongside the macroscopic and submicroscopic. He was absolutely right that it added to the 'learning demand'. However, there is another complication in that many of these key representations (the formulae and equations) are ambiguous as they can represent either the macroscopic level of substances weighed out in grammes (2O2 would represent 64 g of the substance oxygen, although as it is a gas it would normally be measured by volume) or the individual imagined entities of the molecular world (where 2O2 would mean two molecules of oxygen).

Useful ambiguity

This is useful ambiguity for the chemist – but an added complication for the learner who has to follow the teacher's transitions where one moment a symbol reflects a test tube of stuff, and the next some molecule. Because of its role in bridging between the two very different scales at which we explain chemistry I prefer to see these symbols as being along one side of the triangle (whilst separating out the everyday phenomenological level from the technical, theoretical descriptions used by science). However, whatever version of Johnstone's triangle is applied, it has become something of an iconic image in chemistry education.

The chemist's triplet: a variation on Johnstone's triangle (from Taber, 2013)

Another iconic triangle

Derek had not yet been introduced to all this, and he was still operating with burning as a phenomenon:

And why is this important, do you think? Why do you think we study burning?

[pause, c.2s]

I'm not sure.

No one's told you that?

No.

Is it fun, is it a fun topic?

Yeah.

What Derek did seem to have learned well was the fire triangle.

But you have this 'triangle of fire'. So does that mean that fire is always a triangular shape?

No.

So, what's a triangle of fire?

You need three things to make a fire, which is oxygen, heat and fuel.

Okay, so what if I had erm some fuel and some heat, but I didn't have any oxygen, but maybe I've got lots of fuel?

No – wouldn't have fire.

I can't have extra fuel instead?

No.

No?

You need the three things.

What if I've got lots and lots of fuel, and lots and lots of oxygen, but it's very, very cold?

No.

No, that won't work either. So I always have to have the three things?

Yeah.

Derek stuck to his claim – you always needed all three. This is a useful heuristic (useful if ever one is faced with a fire as it tells you can act by just removing one of the three essentials) even if (like most heuristics) it will sometimes fail, e.g.

  • some materials will continue burning in the absence of an external supply of oxygen as they have an internal source;
  • chlorine will support combustion in place of oxygen (but that's seldom a practical issue in everyday situations) ;
  • substances have an auto-ignition temperature (where they can spontaneously ignite), and for a few substances this is around or below room temperature;

These exceptions do not undermine the general utility of the' 'triangle'.

Some useful learning had gone on here – and potentially not just about fire, because the idea that one factor may be limiting on a process is a generally useful principle (e.g., plants grown in a soil depleted in potassium will not thrive, no matter how much sunlight, water, nitrate and phosphate is present).

But the fire triangle, even if it is not supported by a deep understanding of chemical principles, is worth teaching because of its practical value. It seems to offer a heuristic that people accept and recall. And rather like Johnston's triangle, it seems to have become rather iconic. At least, I assume that is why when COVID-19 infection rates were high, the fire triangle was used as a familiar analogy to persuade people to avoid the 'oxygen' of social mixing…

"I like to think of COVID as a fire, if we are the fuel, social mixing is the oxygen that allows the fuel to burn…'"

Read 'COVID is like a fire because…'

Work cited
Notes

1 It has been mooted that fire should be understood as an example the 'fourth' phase of matter, plasma – that is an ionised gas.5 But actually fire is more complicated than this as it contains a mixture of reactant and product molecules and the molecular fragments that form intermediate and/or transition states. Some chemical reactions, when studied at the molecular level, largely follow a single reaction path. But combustion tends to be much more complex with multiple pathways involving many different ions and molecular fragments.

Read: The states of (don't) matter? Which state of matter is fire?

So, fire is a multiphase mixture, more akin to a solution, aerosol, or suspension, than to a gas or plasma.

2 The child does not know this is called fire, and when she is told this she may not realise that such names are social conventions – according to Jean Piaget's research young children may assume that things in the world have (that is, have always had) a name that people have had to learn.

This childish idea reflects superstitious notions about names that are part of some magical systems of knowledge – 'the law of names': the idea that if you know a person or thing's real name this gives you over over them/it.

3 A very influential theory due to Lev Vygotsky takes the distinction between spontaneous concepts formed automatically, and formal taught concepts that are shared through social interaction (such as teaching). These latter kinds of concepts are usually translated from Vygotsky's Russian as 'scientific' though this is meant in the broad sense of any formal field of study. A key point emphasised by Vygotsky was that, assuming the learners could relate a taught concept to existing spontaneous concepts (that is, 'meaningful learning' occurred), they would actually come to operate with a concept which was a hybrid developed from the interaction of the intuitive understanding and the learned technically defined notion – a melded conception.

4 By referring to molecules and ions and electrons as imagined entities, I am not suggesting they are only imaginary. Most (if not all) scientists today see them as real things (even if strictly our evidence is indirect, and they arguably remain theoretical constructs). But a teacher cannot directly show the class a molecule or an electron, even if some types of imaging equipment do now produce representations of individual atoms. For the learners (and I would suggest even the teacher) these are only ever imagined entities. Yet, we expect students to do a good deal of thinking about, and with, these imagined entities.

5 If we are expanding the three states of matter, then there is an argument for making plasma the 5th phase:

  • Bose-Einstein condensates
  • solids
  • liquids
  • gases
  • plasma
  • (quark 'soups'?)

COVID is like a fire because…

Keith S. Taber

Dampening down COVID? (Image by Iván Tamás from Pixabay)

Analogy in science

Analogy is a common technique used in science and science education. In scientific work analogy may be used as a thinking tool useful for generating hypotheses to explore – "what if X is like Y, then that might mean…". That is, we think we understand system Y, so, if for a moment we imagine that system X may be similar, then by analogy that would mean (for example) that A may be the cause of B, or that if we increase C then we might expect D to decrease… Suggesting analogies has been used as a way of introducing a creative activity into school science (Taber, 2016).

Read about analogies in science

Scientists also sometimes use analogies to explain their ideas and results to other scientists. However, analogies are especially useful in explaining abstract ideas to non-experts, so they are used in the public communication of science by comparing technical topics with more familiar, everyday ('lifeworld') phenomena. In the same way, teachers use analogies as one technique for 'making the unfamiliar familiar' by suggesting that the unfamiliar curriculum focus (the target concept to be taught) is in some ways just like a familiar lifeworld phenomena (the analogue or source concept).

Read about science in public discourse and the media

Read about making the unfamiliar familiar

COVID is like a fire…

So, I was interested to hear Prof. Andrew Hayward, Professor of Infectious Disease Epidemiology and Inclusion Health Research at UCL (University College London), being interviewed on the radio and suggesting that COVID was like a fire:

"Sometimes I like to think of, you know, COVID as a fire, if we are the fuel, social mixing is the oxygen that allows the fuel to burn, vaccines the water that stops the fuel from burning, and COVID cases are the sparks that spread the fire. So, we are doing well on vaccines, but there's lots of dried wood left."

There's quite a lot going on in that short statement. If Prof. Hayward had stopped at "sometimes I like to think of COVID as a fire" this would have been a simile where it is simply observed that one thing is conceived as being a bit like another.

Simile offers a comparison and leaves the listener or reader to work out the nature of the similarity (whereas metaphor, where one thing is described to be another, an example would be 'COVID is a fire',  leaves the audience to even appreciate a comparison is being made). Analogy goes further, as it makes a comparison between two conceptual structures (two systems), such that by mapping across them we can understand how the structure of the unfamiliar is suggested to be like the more familiar structure.

That is, there is a mapping (see the figure below) that is based on pairings across the analogy. Here fire and COVID disease are each treated as systems with components that are structured in a parallel way:

COVID (illness): fire
people: fuel
social mixing: oxygen
vaccines: water
COVID cases: sparks

A graphic representation of Prof. Hayward's use of analogy

A lot of us are like kindling

Moreover, having set up this analogy, we are offered some additional information – we are doing well on vaccines (= there is plenty of water to stop fuel burning), but there is still a lot of dried wood. The listener has to understand that the dry wood refers to fuel, and this maps (in the analogy) onto lots of people who can still become infected.

I suspect most people (science teachers perhaps excepted) listening to this interview will not have even explicitly noticed the nature of the analogy, but rather automatically processed the comparison. They would have understood the message about COVID through the analogy, rather than having to actively analyse the analogy itself.

We can stop the sparks spreading the fire

Professor Hayward was asked about contact tracing and suggested that

"…the key thing is the human discussion with somebody who has COVID to identify who their contacts are and to ask them to isolate as well, and that really stops those sparks getting into the population and really helps to dampen down the fire."

That is, that potential COVID cases (that are like sparks in the fire system) can be prevented from mixing with the wider population (who are like fuel in the fire system) and this will dampen down the fire (the illness in the COVID system). {Note 'dampen down' seems to be a metaphor here rather than a true part of the analogy (in which it is the vaccines that have the effect of 'literally' {analogously} dampening down the fire). Stopping sparks mixing with fuel will limit new areas of combustion starting rather than dampening down the existing fire.}

An argument about contact tracing made using the analogy

Again, most people listening to this would likely have taken on board the intended meaning quite automatically, without having to deliberately analyse this answer – even though the response shifts between the target topics (the COVID disease system) and the analogue (the fire system) – so the sparks (fire system – equivalent to infectious cases) are stopped from getting into the population (COVID system – equivalent to the fuel supply).

This is reminiscent of chemistry teaching which slips back and forth between macroscopic and molecular levels of description – and so where references to, for example, hydrogen could mean the substance or the molecule – and the same word may have a different referent at different points in the same utterance (Taber, 2013). Whether this is problematic depends upon the past experiences of the listener – someone with extensive experience of a domain (probably most of the audience of a serious news magazine programme understand enough about combustion and infection to not have to deliberate on the analogy discussed here) can usually make these shifts automatically without getting confused.

Fire requires…AND…AND…

An analogy can only be effective when the analogue is indeed more familiar to the audience (you cannot make the unfamiliar familiar by comparing an unfamiliar target with an analogue that is also unfamiliar) so the use of the analogy by Professor Hayward assumed some basic knowledge about fire. Indeed it seemed to assume knowledge of the so-called 'fire triangle'.

Three factors are need to initiate/maintain combustion: fire may be stopped by removing one or more of these.

This is the idea that for a fire to commence or continue there need to be three things: something combustible to act as fuel; AND oxygen (or another suitable substance – as when iron filings burn in chlorine – but in usual circumstances it will be oxygen); AND a source of energy sufficient to initiate reaction (as burning is exothermic, once a fire is underway it may generate enough heat to maintain combustion – and sparks may spread the fire to nearby combustible material). To extinguish a fire, one needs to remove at least one of these factors – water can act as a heat sink to decrease the temperature, and may also reduce the contact between the fuel and oxygen. Preventing sparks from transferring hot material that can initiate further sites of combustion (providing energy to more fuel) can also be important.

Unobtrusive pedagogy

The quotes here were part of a short interview with a broadcast journalist and intended for a general public audience. Prof. Hayward introduced and developed his analogy as just sharing a way of thinking, and indeed analogy is such a common device in conversation that it was not obviously marked as a pedagogic technique. However, when we think about how such a device works, and what is expected of the audience to make sense of it, I think it is quite impressive how we can often 'decode' and understand such comparisons without any conscious effort. Providing, of course, that the analogue is indeed familiar, and the mapping across the two conceptual structures can be seen to fit.

Works cited:

Taber, K. S. (2013). Revisiting the chemistry triplet: drawing upon the nature of chemical knowledge and the psychology of learning to inform chemistry education. Chemistry Education Research and Practice, 14(2), 156-168. doi:10.1039/C3RP00012E

Taber, K. S. (2016). 'Chemical reactions are like hell because…': Asking gifted science learners to be creative in a curriculum context that encourages convergent thinking. In M. K. Demetrikopoulos & J. L. Pecore (Eds.), Interplay of Creativity and Giftedness in Science (pp. 321-349). Rotterdam: Sense. (Download the author's manuscript version of this chapter.)