Hardness of floors

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Brennan - 29 Dec 2006 10:38 GMT

I am a doctor in the Children's Hospital in Manchester, United Kingdom.
Among other things, I deal with children who injure themselves falling
from heights on to indoor floors. Parents, lawyers and other doctors
often ask me whether injuries are more likely when children fall onto
hard floors such as concrete rather than softer ones such as carpeted
floors. I am trying to find someone who knows how to measure the
hardness of floors. Can anyone help me? Brennan

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Bob Morrison - 29 Dec 2006 15:42 GMT

In a previous post Brennan wrote...

> I am a doctor in the Children's Hospital in Manchester, United Kingdom.
> Among other things, I deal with children who injure themselves falling
[quoted text clipped - 3 lines]
> floors. I am trying to find someone who knows how to measure the
> hardness of floors. Can anyone help me? Brennan

Common sense will tell you that someone falling onto a concrete floor will
more likely sustain an impact injury that some falling onto a heavily
carpeted floor.

If you insist on having test data, then I think that a local testing
laboratory might be able to devise some sort of impact test. Or you could
devise you own test. Perhaps you could use hard boiled eggs dropped from
various heights onto various surface types. Of course, the eggs will crack
differently depending on whether or not they impact on the side or on the
ends. Eggs are stronger when dropped on their ends.

Obviously with children, the damage inflicted in a fall will depend on how
they land as well. Land on their bottom and almost no damage -- land on
their head and there is potential for serious damage.

Signature

Bob Morrison, PE, SE
R L Morrison Engineering Co
Structural & Civil Engineering
Poulsbo WA
bob at rlmorrisonengr dot com

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dpb - 29 Dec 2006 16:29 GMT

As Bob Morrison points out, the actual hardness of the floor is only
one variable, and probably not the most significant one at that in the
severity of injury.

It is not at all difficult to ascertain the actual hardness of a
flooring material itself such as wood, tile or concrete. That
measurement, however, isn't feasible for soft or resilient materials
such as carpet or even the cushioned vinyls, say.

What is really significant is more nearly described as the elasticity,
but again as Bob points out, it only is common sense that a poured
concrete floor has the ability to impart more damage for a specific
fall height, attitude, etc., than a carpeted one.

I really see little point in the question other than the obvious one --
litigation. Can you explain in more detail what your end result of the
question is intended to be? That might provide futher insight on how
one might investigate the issue. I would think the best data, however,
would be empirical observation of reported accidents supported by
decent forensic examination of the accident site and reconstruction of
the accident itself to generate the parameters thereof. I would be
surprised if the medical literature doesn't have at least something
along these lines already.

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Matt Whiting - 29 Dec 2006 16:56 GMT

>>I am a doctor in the Children's Hospital in Manchester, United Kingdom.
>> Among other things, I deal with children who injure themselves falling
[quoted text clipped - 17 lines]
> concrete floor has the ability to impart more damage for a specific
> fall height, attitude, etc., than a carpeted one.

It isn't just hardness or elasticity, but also mass of the material and
other variables. The issue for soft tissue damage is likely related to
the stress applied to the tissue and this is mainly a function of the
area over which the load is applied. A hard floor that isn't very
resilient will concentrate the force over a small skin area, whereas a
floor that is resilient will allow the head to sink into it greatly
increasing the area over which the force is distributed. From a brain
injury perspective, the main issue is likely to be the acceleration
experienced. This is a function of both static and dynamic nature of
the material. For example, water is very "soft" and resilient
statically, but can be very "hard" dynamically due to its fairly high
density. So, if you hit water hard, it will impart huge acceleration
forces, whereas, in a static sense it imparts almost no force at all.
That is one reason that wood floors are so much more impact friendly
than concrete. They are both lower mass and thus provide less dynamic
force at impace, but they are also more resilient to allow more
spreading of the impact area on the soft tissue.

This is obviously a very complicated issue that goes well beyond the
hardness of the floor material.

Matt

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bowgus - 29 Dec 2006 17:34 GMT

Hardness is not the term you should be focussing on. Hardness typically
refers to the ability to resist scratching (e.g. diamond harder than
glass). You might look instead into shock absorption - flooring. Or how
about keep it simple. Drop a basketball onto different surfaces ...
concrete, carpet with underpad, ... or ... "this is your head on
concrete, this is your head on carpet." ... and leave it at that :-)

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CWatters - 29 Dec 2006 22:24 GMT

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Homeowner Forum / Construction / December 2006

Hardness of floors