Hello Israel:
Unfortunately, safety standards only address one of the
critical parameters, temperature, when specifying
requirements for protection against a burn injury.
You are absolutely correct that a metal surface with a
temperature exceeding 50 C is capable of producing a burn
injury.
There are four parameters that must be taken into account:
1. temperature
2. thermal conductivity of the material
3. thermal capacity of the material
4 duration of contact
One can easily touch aluminum foil at 100 C and higher for
an indefinite duration because its thermal capacity is very
low.
One can easily touch plastic at 100 C for an indefinite
duration because its thermal conductivity is very low.
One cannot touch a 25 mm or larger cube of aluminum at 50 C
for longer than 10 seconds without burning the skin because
its thermal conductivity and thermal capacity are high.
There is no regulatory source that addresses all four
parameters. Instead, you must consider your training in
the field of thermodynamics, and you must consider the
literature where the burn parameters of human skin are
published. If you look, you will find published data
relating skin temperature and duration to pain and to skin
burns.**
Unfortunately, the authors of our various safety standards
chose the BOGSAT* method of determining safety rather than
doing research.
The requirements you mentioned are indeed inadequate. But,
you have already determined that. So, using your training
as an engineer, you can make your product safe for both the
hot surfaces and the hot air in spite of the standard.
Best regards,
Rich
-------------------------------------------------------------
Richard Nute Product Safety Engineer
Hewlett-Packard Company Product Regulations Group
AiO Division Tel : +1 858 655 3329
16399 West Bernardo Drive FAX : +1 858 655 4979
San Diego, California 92127 e-mail: [email protected]
-------------------------------------------------------------
* BOGSAT = Bunch Of Guys Sitting Around Talking.
** Stoll, Alice M., "Thermal Properties of Human Skin related
to Nondestructive Measurement of Epidermal Thickness,"
Journal of Investigative Dermatology, September, 1977,
pp. 328-332.
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