Hi Brad:
I am the one who proposed the limit of 15 watts for 3 seconds.
With others, I performed several experiments to ignite plastic materials
with various resistive power dissipating devices. I found that ignition
could occur with 50 watts, but not easily at 15-20 watts.
Most plastic materials will not ignite at at less than 300 C, but are likely
to ignite at more than 300 C, with some plastics as high as 450 C.
Time of exposure to a heat source is a necessary element in heating any
material and attaining self-ignition temperature.
However, 15 watts is usually heat-sunk by the local environment, so heating
a flammable material to more than 300 C is not likely in 3 seconds.
Consider a 15-watt incandescent light bulb; you can touch it indefinitely.
By the way, a candle flame is about 50 watts. A match flame is closer to 15
watts.
Flint and iron or steel breaks off a piece of iron or steel which bursts
into flame (iron and steel are pyrophoric materials) that ignites the
tinder. Because of the mass of the piece, I suspect that it is 50 watts or
more.
So, 15 watts for less than 3 seconds is not likely to start a fire.
Best regards,
Richard Nute
formerly chief technical officer, IEC TC108
From: Willard, Bradley <bradley.will...@zebra.com>
Sent: Thursday, July 26, 2018 2:29 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: [PSES] PS1 limit?
Hello Everyone,
I'm looking for guidance on how the PS1 limit of 15 watts for 3 seconds in
IEC 62368-1 was determined.
Thanks in advance!
Best regards,
Brad
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