> I don't want to re-invent the wheel, but I'm looking to find a simple
> way to communicate the idea that some systems don't need protection,
> others need protection, others need protection that will still protect
> even with a single-fault present anywhere, and so-on. Somewhere somebody
> must have codified this idea for example with type 0, type 1, type 2,
> etc. I'm sure there are standards out there for this - can anyone point
> me to one or more?
>
> Thanks,
>
> Jim
Hi Jim:
The new IEC 62368-1 standard does exactly what you wish
for.
The standard asserts that injury (or fire or whatever)
is due to a transfer of energy (from an energy source)
to a body (or other susceptible part).
Energy sources are classed as:
Class 1: Little or no perceptible effect on the
body (or other susceptible part) even in the event
of a single fault. No safeguards are required.
The energy source is inherently safe.
Class 2: Sensation to pain on a body part but no
injury or equivalent on a susceptible part) even
in the event of a single fault. At least one
safeguard, e.g., a basic safeguard, must be
interposed between the energy source and a body
part (or other susceptible part).
Class 3: Severe pain or injury to a body part or
equivalent susceptible part). At least two
safeguards, e.g., basic plus supplementary, or
a reinforced safeguard must be interposed between
the energy source and a body part (or other
susceptible part). The energy source is inherently
hazardous.
The only difference between what we do today and this
new standard is the inclusion of the Class 2 energy
source criterion. Class 2 was included because most
telephone circuits fall between Class 1 and Class 3.
The standard applies this concept to electric shock,
electrically-caused fire, thermal injury, mechanical
energy, radiated energy (acoustic, electromagnetic,
and optical), and chemically-caused injury.
All of these energy sources have continuous
gradations from low (marginally detectable) to high
(injurious). Most energy sources have well-defined
and researched limits for "low" (non-hazardous).
Best regards,
Richard Nute
Product Safety Consultant
San Diego
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