I've been asked my views on a recent #forensic #fibres paper published by @NUCFS describing 'contactless' fibre transfer. Longish thread, but firstly big thank you to @Kjsher for sharing with me a copy of the work. /1
Bravo to Kelly and co for an exceptional piece of work. Those who have access to paywalls etc can find the paper here. /2
sciencedirect.com/science/articl…
Reaction to the work, particularly to this tweet from @CrimelineLaw
Joking aside, no surprise there, this is twitter after all and who hasn't responded to a headline without checking the actual document first. /4
Perhaps my views may help clarify some issues for those who take the headline as meaning that this work somehow calls into question the validity of textile fibres as #forensic evidence. Spoiler alert - it doesn't. /5
The paper is entitled "A study on contactless airborne transfer of textile fibres between different garments in small compact semi-enclosed spaces ". So a bit of background first. /6
The fact that fibres exist in the air is not new as @defencebrief points out. Studies have shown that outside surfaces such as window frames for example, tend to have fibres (mainly cotton) on their surfaces
Surfaces such as window frames tend to have very little physical contact with human beings so such fibres are likely to have been carried there on the air. Why cotton? Most common fibre type worn by people and it sheds well from garments. So we know this already. /8
What this study attempts to do is to quantify the number of fibres that could transfer to surfaces via the air, this is new and hasn't been a feature of previous research. /9
So what did the research team do? In summary, they put 2 people in a lift, one wore a "donor" garment, one wore a "recipient" garment. The two people had no contact. /10
Immediately after the "recipient" exited the lift, they counted the number of fibres from the "donor" garment on the surfaces of the "recipient" garment. /11
They repeated this 6 times with 4 different donor and recipient fabrics and looked at primary and secondary transfer scenarios making 48 experiments in all /12
In a little more detail. The lift measured1.3x1.7x2.3m. This is a very small space. The farthest away anyone can be from another person, diagonally in the corners, is just over 2m. It would fail social distancing in a post covid world /13
The donor entered on one floor and stood in the corner. The recipient entered on another floor and stood in the diagonally opposite corner. So the donor is in the elevator for a period of time (unknown) before the recipient enters /14
They both stay in the elevator for 10 mins, before exiting separately on different floors, so both parties would come into much closer proximity when the first party to exit, exited the lift. /15
Other people do enter and exit the lift during the experiments, these are not party to the study being undertaken and have no knowledge of it. The lift essentially operates entirely normally throughout the experiments. /16
It's not clear from the data how many people entered the lift for any given experiment, although this data is recorded. It's not clear where they stood in the lift or whether they may have had contact with either or both parties. /17
If they were British I would suggest that contact was unlikely 😉, but it is a confined space. Over the course of all of the 48 experiments it appeared that 10 people entered the lift /18
The picture this paints of the experiment is one where the recipient will enter either a "cloudy" box where the air contains airborne fibres or a "clear" box where there are very few or no airborne fibres. /19
The research team found both outcomes and concluded that the type of fibre used in the construction of the donor garment was the major factor in determining whether the box became cloudy or stayed clear. /20
A fibre needs to be (a) shed to the air and (b) persist in the air long enough to land on the recipient. It is not merely a question of fibres but of aerodynamics. Not a surprise that the shorter, thinner, lighter fibres were superior vehicles for airborne transfer /21
The number of cotton and polyester fibres found on the recipient was very interesting and should give caseworkers reason to pause if ever they dismissed airborne transfer of these fibre types solely based on the number of fibres found /22
But perhaps what was more telling was for wool and acrylic fibres, in an experiment which largely optimised the environment for maximum airborne contamination, airborne transfer was negligible. /23
In effect this study could be relied on by some to dismiss airborne transfer entirely in cases where even relatively few numbers (>2) of these fibres are found. /24
The authors are quite right to point out that in cases where very few acrylic or wool fibres are found (1 or 2 in this data) that such results would be in keeping with both airborne transfer and physical secondary transfer, however that is true for all fibres. /25
So after all that, what does it mean? This is a very welcome piece of research of very high quality. It improves our knowledge of airborne transfer. /26
Experts will have to get to grips with it because the lawyers have a headline which they can use to either attempt to strengthen, or more likely, attempt to weaken fibre evidence. /27
I would recommend that if the results of this study are used to bolster a case for airborne transfer that do not include people in a lift 1.3 x 1.7 x 2.3 together for 10 mins that such a scenario should be tested experimentally, there are so many complex variables at play. /28
For example what would be the outcome if the recipient had entered first? What about the possibilities for airborne two-way transfer? what would happen if the period in the lift where the two were together was very short? what if the lift were packed with people? /29
What if the lift was bigger? Can we measure the radius of the cloud of airborne fibres that are emitted by cotton garments? Hopefully there will be follow ups to this study /30
If defence teams seek to rely on this data they should understand that they are asking the court to believe that their client was in a confined space with the other party for at least 10 mins, but with no contact at all /31
It does not support a defence of merely passing by somebody on the street without knowing it, or sharing the same train etc. In some cases this may be a viable approach, but it would largely depend on other evidence such as CCTV or witness statements. /32
In reality all of these assessments should be done by the prosecution prior to undertaking fibre examinations as part of due diligence /33
Sadly our fragmented CJS is such that fibre experts, if they still exist in England and Wales, are not always provided with the information they need by the police, including CCTV. /34
Defence teams, never assume that the prosecution scientist has the same information you do, or that the police have. The scientist will always review any findings when 'new' information comes to light. Statements are not written in stone. /35
You must hire your own expert to review. They will know what to ask, who to ask, where to find it, and what it all means for you /36
Great piece of work which improves our understanding of airbone transfer of fibres in enclosed spaces. It doesn't undermine the integrity of fibre evidence. The likelihood of finding matching fibres by chance remains exceedingly low. /37
Our understanding of how fibres persist on surfaces has not been altered by this study, in fact the findings bolstered it. /38
Once again exponential loss was observed with all fibres transferred secondarily being lost within 2 hours ( in fact most were lost entirely within 30 mins). This was most pleasing for me personally - I will explain that more in the future 😉 /39 /Ends
