[Stoves] health impact follow-up (fixed broken image)

[Marc-Antoine Pare]

Hi everyone,

Thanks for the discussion so far. I've looked at the health numbers for
improved cook stoves in some more detail.

I found two major approaches to quantifying the impact on health by stoves:
long term studies and modeling based on exposure response.

They both point to the same overall conclusion: improved biomass cook
stoves will only reduce a small number of the “4 million deaths” you hear
about from indoor air pollution.

Also, it appears that there isn't an existing biomass technology that will!

Please bear in mind that this is just a few days of compiling results from
research. All of these conclusions are tentative. I welcome any and all
criticism. The reading has been quite educational so far.

One note at the start: the studies here consider the negative effects on
respiratory health by particulate matter (PM). The studies I read note that
this is by far the largest contributor to the burden of disease from indoor
air pollution.


*Long-term studies*

*Effect of reduction in household air pollution on childhood pneumonia in
Guatemala (RESPIRE): a randomised controlled trial (2011)*

523 households involved. About half get an improved plancha stove, which
reduces exposure about 50%. Eighteen months later, there was a 22%
reduction in cases of pneumonia.

Note that in this population, there were 9 deaths attributed to pneumonia.
This is important later.

Also important to note is that aid workers regularly coached these
households in usage and maintenance.


*A Recipe for Success? Randomized Free Distribution of Improved Cooking
Stoves in Senegal*

98 households get a stove for one year. Respiratory disease symptoms for
cooking women drop by 8%.


*UP IN SMOKE: THE INFLUENCE OF HOUSEHOLD BEHAVIOR ON THE LONG-RUN IMPACT OF
IMPROVED COOKING STOVES*

5 years, 15,000 Indian households (!) “We find no evidence of improvements
in lung functioning.”

The critique of this study is that they used mud stoves with chimneys that
weren't all that clean-burning.

*What the long-term studies tell us*

I was surprised that the number of stoves required to impact health was so
high. In the Guatemala study, you need 250 stoves to prevent about 10 cases
of pneumonia.

Another interesting thing to note is that I didn't find any studies that
monitor big enough populations for long enough to quantify how many
*deaths *are prevented by improved stoves. Again, in the Guatemala study,
the stoves saved somewhere between 1-5 lives. This number is so small that
it's really tough to extrapolate it at all.

Clearly something funny is going on here. Why exactly are the numbers so
small? Did people use the stoves incorrectly? Would better stoves have
helped? And why did nothing happen in India?

One approach to answering these questions is to dig in to the mechanism for
saving lives with stoves. We do this with the exposure response to
pollutants.


*Modeling based on exposure-response*

Health impact from exposure to PM is well studied. Exposure amount predicts
quite accurately future health problems. This is great because it let's us
start answering the question: just how clean do stoves need to get to
meaningfully impact health?

We can really get into a lot of detail here. It's a dissertation's worth of
calculation to come up with these numbers (see: THE DEVELOPMENT OF
NUMERICAL TOOLS FOR CHARACTERIZING AND QUANTIFYING BIOMASS COOKSTOVE IMPACT)

Kirk Smith presented a summary of what exposure-response can tell us about
stoves at the Clean Cooking Conference just this May.

Here's the graph:

[attached]

The key note is that a rocket stoves “leaves ~80% of the burden [of
disease] untouched”. That means that even if we give everyone a rocket
stove, only 20% of the 4,000,000 deaths from IAP will be affected.

Here's the reasoning. The red line in the graph is called the
“exposure-response relationship”. It's a log-linear relationship. That
means that most of the damage from PM exposure occurs from zero exposure to
a very small amount of exposure.

It turns out that improved cook stoves – even the very fancy fan stove
developed by Phillips – don't reduce emissions below that initial amount of
very dangerous exposure.

Kirk Smith provided this summary in London: “Current Health Evidence shows
now that even major reductions (<90%) in emissions still lead to small
health improvements”


*Conclusions: just how small?*

We can do a back-of-the-envelope analysis to tell the story of the numbers
presented here. If we assume six billion people use primitive stoves, then
one hundred million of them is 1/60 of the total. 1/60 of the four million
deaths worldwide is ~67,000. Rocket stoves would save 20% of those lives
according to the exposure-response model: just 13,400.

So, you get out 100,000,000 stoves, and you save 13,400 lives. This also
assumes that you achieve the PM emissions reductions in practice. There are
mountains of evidence (academic and practical) that this is not the case.

I am trying to find what I am missing here. I really expected the link to
be much more clear and significant. Is there some other reason that stoves
are promoted besides health benefit? Is there some overarching strategic
goal that I'm missing?

Really, I'm looking for some number to tell the story. All the numbers I
have found point to the fact that stoves, even the very best ones we have,
won't move the needle on deaths from IAP.

I would be very happy to be wrong about this. I know that development
issues can be confoundingly complex, and I would welcome another
perspective on this.

One silver lining to all of this is that I think it would be great for
technology developers to hear that current technologies are totally
inadequate. There's nothing like an impossible challenge to galvanize the
inventor :)

- Marc Paré
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