Tip:
Highlight text to annotate it
X
[ Music ]
>> Thank you David.
Our next speaker is Louisa Marsh,
from LGC Forensics, out of the UK.
We welcome her, and she will be talking to us about airbag dust.
The name of her paper is "*** Goes the Airbag:
Using Dust from Deployed Airbags as Trace Material
in Automotive Crimes".
>> Louisa Marsh: Thank you.
Good morning.
First of all, I'd like to thank everybody for the opportunity
to talk to you today about my research
and for attending my talk.
Like every good story, there's a beginning, a middle, and an end.
And as a bench caseworker, as most of you guys are,
it started really with a problem.
Cases were coming in to try
and identify whether somebody was a driver in a vehicle
at the point of an impact.
Now, traditional techniques generally look
at whether you can tie someone to an airbag that's detonated;
for example, by looking for things like fibers or hairs,
or even blood, and maybe fingerprints, with the point
to try and identify whether someone was actually the driver
or the passenger in a vehicle, at the point of an impact.
But there are some issues and some problems with this,
although they're fairly routine.
There has been a study that showed in 20% of cases,
there was no usable DNA from airbags which had exploded.
And this generally is not
because there's a poor technique.
It's generally because they're complex mixtures.
Airbags are not packed in clean environments;
and so quite often, when they detonate,
you end up with a mixture coming off.
The other problem with cases in -- such as this type,
are when there are suspects
who have prior legitimate access to a vehicle.
So maybe it's their car,
or maybe that they have been allowed to drive it in the past.
And the next logical step, really, for us was to look
at the airbag debris itself.
Anyone that's ever examined airbags themselves can't fail
to notice the fact that they're extremely dirty items.
When you pick them up, they've got a lot of dust on them,
and that dust is actually spent propellant.
And being a trace person at heart,
I realized that this is going to be --
this is going to be a good target, really.
Moving on to some of the background, if you have a look
at the picture here -- the picture on the left --
this is a typical driver's airbag that's been detonated.
And I draw your attention to the fact that the middle
of the airbag actually has some stitching in it.
And when I embarked on this research,
I didn't know how important that stitching was going to be.
So this particular one has red stitching.
Now, I've spoken to lots of people who work
in the airbag industry, and they tell me that the stitching
on airbags is there purely to identify -- in terms of color --
you know, which airbags they're putting in vehicles.
And the colors are random.
So some are pink, some are blue,
some are green, and some are red.
And they also use different dye techniques
to dye these particular airbag stitches.
The picture on the right is actually a passenger airbag
that had been unfolded, so that particular one hadn't detonated.
A little bit more background.
I'm sure people are very aware of the fact
that airbags are designed as safety features in vehicles.
The whole idea is that as a collision occurs,
you actually ride down on these airbags, so your face
and your body sort
of essentially are cushioned by the airbag.
And they inflate extremely fast, in an extremely hot manner.
And there have been some great papers published which look
at the scorch marks on clothing or on skin of people who've come
into contact with exploding airbags.
So that's always another technique that could be used,
if you're trying to tie someone up to an airbag themselves.
This is a busy slide, and I'm not going to go
through all the background.
But quite often people assume that airbags are packed
with cornstarch or talc.
And that's actually a very old technique, now.
The original airbags back
in the early 90s used lubricating powders to try
and stop the lining from sticking to it.
So the old-fashioned idea of people sort of looking
as if they've had sort of bags of flour thrown at their chests,
when they've been in an accident, you could still find,
but they would be extremely old vehicles.
Nowadays, modern airbags tend to have silicon lining
on the inside and no new pre-lining,
so the need for lubrication has gone down.
Needless to say that each individual airbag going off is a
pyrotechnic explosion and hence has starting materials
and spent propellant.
And it is quite an explosion, actually.
I don't know if anyone's ever been in the misfortune to have
to come into contact with an airbag at the business end,
so to speak, but they really, you know -- they really go ***.
They're very, very forceful explosions.
So what particles are produced?
Well, the manufacturers tend to be very cagey
about letting you know what they've put into their airbags.
So there are commonalities between airbags
with starting materials, but they also often add sort
of special ingredients that they don't like to tell you about.
But the most important thing I found out during my research is
that the starting materials is really only the first part
of the story, because in any good reaction --
as proper chemists know -- it's the environmental issues
that also have an effect on that particular explosion.
So, in my opinion, every airbag going off really is a
unique explosion.
So if you took a hundred airbags
with the same starting materials, it is quite likely
that you will end up with slightly different particles
coming out at the end, because each one really would be a
different temperature, a different pressure.
There has been some research done in the past --
there's been some excellent papers studied --
I've added some references at the end of this talk --
looking at airbag debris, from the point of GSR.
So studies have shown
that particles produced during airbags exploding actually are
very similar to GSR particles, down to one or two microns.
And in some instances, it's not possible to tell the difference
between these GSR particles from an airbag
and a GSR particle perhaps that's come from a firearm.
And one paper actually noted that they had not seen any
such thing as a unique airbag particle.
That's really the background to where I was going.
We had the opportunity to conduct some research,
and unfortunately, my company couldn't quite rise
to buying vehicles and crashing them,
although I did try and ask.
But we went to the next -- the next possibility,
which was to attend our local scrapyard,
found a very helpful scrapyard,
who actually detonated the airbags for us.
And that gave us a unique opportunity to teach each --
to treat each individual vehicle as a separate experiment.
And they're actually deployed using a nine-volt battery,
so you sort of ripped the housing off underneath the
steering wheel, and the engineer was able
to deploy the airbag while we were standing and watching.
And if you've never see these things go off,
they really do go off with a ***, and they sort of smoke
for ages -- extreme heat.
We had to stand well back,
because I am told they can take glass out,
as well, when they go off.
Because we were able to treat each individual one
as an experiment, we actually were also able
to leave open tape lifts on the seats,
to try and capture the powder as it moved around the vehicle
at the point of detonation.
And we also SEM stubbed the inside of the vehicle, before --
before and afterwards.
And unfortunately,
those particular SEM stubs haven't been processed yet,
so I know a lot of you guys are GSR experts.
I'm afraid that really is beyond the scope
of this particular talk.
Then once the airbag had deflated and wasn't so hot,
so I wasn't going to burn myself,
I then taped the front of the airbag.
And the point of that really was
at that point the airbag was still in situ.
It hadn't been in contact with the inside of the vehicle.
And so, by taping the front of the actual airbag was going
to try and gather some information about what kind
of extraneous fibers or other extraneous material were
actually present on the airbag after it exploded,
before it had come into contact with the vehicle.
I'm guessing those of you who are caseworkers,
if you get items in, you often don't know the story behind
what's happened to it.
And obviously this was a unique opportunity
to know exactly what's happened to my items.
Once we taped the front of the airbags, we're then able
to cut the airbags out and forensically bag them.
And we actually undergone --
underwent a couple of experiments, where we were able
to put dummies in the front seats, as well,
to see what happened to the clothing that they were wearing.
And again, unfortunately,
those clothing items haven't been processed yet,
so that's a story for the future.
If you have a look at picture Number 1, this is a photograph
after the airbags exploded and then I half cut it out,
so it shows the back of the steering wheel.
Picture Number 2 is the open tape lift behind the steering
wheel itself, so I was able to capture some of the particles
as they flew around the vehicle.
Number 3 is the open tapes on the back of the seat,
and actually put the open tapes on the passenger seat
and the driver's seat, to try and gather some information
about how far these particles were flying.
And Number 4 shows a couple of the dummies that we put
in the seats in two experiments,
and they were wearing brightly-colored T-shirts,
with the idea that we could try and find out if those fibers
on those T-shirts turned up on the airbags.
Once the airbags had actually been cut out of the vehicle,
we got out of the rain --
because it was chucking it down that day,
went back to the laboratory, and actually opened up the items
and tipped all the dust out from the inside of the airbag.
And anyone that's ever looked at these airbags will realize
that they are really, really dusty.
And it's immediately obvious there's a huge difference
in the dust that's coming out of them.
And there's a -- just four descriptions here of --
four photographs here of some
of the petri dishes that we tipped out.
And they really ranged from, you know, dark, dark,
black carbon material down to sort of white, fluffy material.
So there was a huge range there.
And then going back to simple light microscopy techniques,
all the dust was looked at with a low-power microscope,
to identify what on earth we'd got here.
And having identified the morphology
of these particular particles, we started to move
on to high-power techniques, so polarized light microscopes,
and also what flourescent effects were going on.
Alongside looking at the scrapyard samples,
also had the opportunity to collect some dust
from real casework samples.
So this results table here shows some
of those casework samples themselves.
And the dust in these was actually processed alongside the
airbag -- airbags that we took from the scrapyard.
All vehicles have round airbags in the driver's seat --
thank you -- round airbags in the driver's seat
and rectangular airbags in the passenger seat.
And moving on to the scrapyard samples, again,
we started noting whether there was linings
in the actual vehicle airbags themselves.
Quite often what was happening is that there was no lining
at all, or there was a sort of a central lining
over the front of the airbag.
Remember the first photograph I showed you
with the red stitching on the inside.
On the back of that red stitching is actually a
partial lining.
So quite a lot of the airbags we saw had these partial linings.
Didn't have a choice, though, with the vehicles that we chose.
Unfortunately, we were very tied
by what vehicles were available to us.
I mean, the scrapyard that we attended, the vehicles were sort
of all higgledy-piggledy and on top of each other,
and it became a safety issue.
So really, we exploded whatever airbags we could safely get at.
We weren't too picky.
But it did mean that we were sort of almost stuck
with the older-type vehicles.
So it was a real -- it was real range of vehicles
that we ended up with.
So my results.
By looking at all the individual dust particles that we got off,
we started to identify what I've termed as forms.
And rather than looking at the GSR-sized particles --
the one or two microns that David was talking about --
I really went for the big boys, really --
anything that I could pick up with a pair of tweezers
and manipulate onto glass slides.
So really, between sort of 40 microns and up to 600 microns,
really, were the ranges that we saw.
And I identified 50 different forms --
50 different morphological forms that I would be comfortable
under low-power, stereo microscope
as saying different -- were different from each other.
All these dust forms were actually analyzed using
polarizing microscopy.
And one of the interesting points that I noticed is
that virtually none of them exhibited any birefringence.
And thinking that through, that makes perfect sense to me,
because as part of the pyrotechnics explosion,
these forms are being created extremely --
under extreme heat and then cooling extremely fast,
so there's no crystallinity forming.
So that actually kind of made sense to me.
Many of these different forms cropped up again
and again in different airbags.
But of all the airbags that we looked at,
none of them had exactly the same ratios.
And often there was maybe three or four forms in one airbag,
but perhaps in another airbag we were seeing maybe 20
different forms.
So there was an enormous variation
between the airbag dust themselves.
One of the most distinctive and interesting forms I saw is --
it's what I've described as worms.
And that's exactly what they look like: Small, glass --
glassy-like materials that contain air bubbles,
and they are very wormlike.
And we kept seeing those again and again.
They kept cropping up in the debris.
And they kept cropping up in different colors.
Going back to the beginning of my talk, where we were talking
about how important the colored stitching was, it took a while
to cotton on to the fact that there was quite a lot
of correlation between the color of these glassy-like worms
and the color of the stitching
that was actually on the airbag itself.
Preliminary results from the tapes inside the airbag are
indicating that approximately half the level of dust
from the exploding airbag is reaching the passenger side
as the driver side.
So although that's expected, it is a limitation,
because I don't think you would ever be comfortable saying
if someone's got dust on them,
that they were definitely the driver; because knowing
that the dust is flying around the vehicle means sitting
as a passenger they would also pick that up.
So that is a limitation of this -- of this procedure.
Having a lining inside each airbag, as well,
did reduce the amount of debris, obviously.
There's less being thrown outside the airbag itself.
But in every single airbag,
we did end up with a significant quantity of debris --
at least half a teaspoon from each airbag.
So this pyrotechnic explosion is producing spent particles
in every case that we looked at, with one exception.
We had one airbag that we took from the scrapyard
that hadn't detonated, and that became a lovely control,
because obviously there was no particles inside that for us.
So moving on to some of the forms that we saw.
I'll run through these fairly quickly.
The most common form that we saw was this sort
of flat particle -- the silver-grey particle,
and that turned up in almost half the airbags.
And there's nothing really particularly special
about that one.
And although it was there, you know,
I wouldn't put any inference on the fact that it was there,
because it was so common.
The bottom left form, obviously, is the glassy-like worm
that I was talking about, and that turned up in six
out of the 23 airbags that we looked at in total.
I'm going to skim through quickly the next slide,
just to show you -- the next two sides,
just to show you here some of the correlations that we noted
between the airbag stitching and these forms themselves.
And my hypothesis -- as yet untested,
and I'm very interested to see what you guys think --
is that the dye actually in the airbag stitching is sublimating
at the point of impact and getting caught
in the formation of these worms.
So I think this is going to be -- of all my results,
this is going to be potentially the most diagnostic.
And it came up again and again.
The one at the top, this Toyota, had blue stitching.
We ended up with blue worms.
Orange stitching, orange worms.
And it was a correlation that we saw again and again.
So just -- I'm afraid I'm going to run out of time to go
through this, but this is just showing some of the fibers
that we actually found on the front of the airbag,
and there was a significant number.
There was also hairs cropping up on this, as well.
So just as a conclusion, dust was produced in every single --
in every single deployed airbag.
The dust recovered was distinctive and was searchable
with a low-powered microscope and a pair of tweezers.
The color of the stitching is extremely important,
because of the possible sublimation
of the dye coming out of that.
I think that it's fair to call each explosion a unique
detonation, and, subsequently, it's not unusual
to expect what you end up with varying slightly
in each individual case.
What we're finding it's best actually to shake the items
of clothing to recover the debris, because in trace terms,
these things are quite big.
I wouldn't recommend taping them,
because the adhesive does actually distort them.
We did find a significant number of fibers on the front
of the airbag, because these things are not packed
in clean environments, and that's something just
to be careful, if you're trying
to use fiber evidence to link them.
And of course, the limitation:
I would never be comfortable saying someone was the driver,
simply because we know that this dust moves
around the inside of the vehicle.
And again, this -- the distinctive forms show melting
and -- heating, melting and cooling -- rapid cooling.
And as expected, it shows very little birefringence.
I have included a case study, which will be available
on the website, if you would like to have a look
after the end of the conference.
Unfortunately, I haven't got time to go through it here.
But this -- the results of my research have actually been used
in anger in about four or five cases now
and actually have been accepted in court in the UK,
so actually adds quite a nice validity to the story.
And, you know, if you'd like to catch me after this session,
I'm more than happy to show you this particular case study,
if you are interested.
One final -- one final slide.
I just like to say a massive thank you to my two students,
who've been squirreling away for the last couple of years
on this project: Anna Kelly, who was my student back in 2000;
and Jack Gallagher, who's been working away this summer on it.
So I'd like to say a massive thank you to them
for the processing of all the different forms.
Obviously, it's been an enormous amount of work.
And, obviously, I'd like to say thank you to you guys very much
for listening to my presentation.
[Applause]