"Intrinsically Safe" requirement - EtO sterilization of device with Battery

G

gruhfy

#1
Thank you everyone, I have gotten a lot of great information from past posts. I finally have a topic which is new thread worthy.

We manufacture a battery powered device which gets EtO exposed, and my sterilizer just brought this to my attention:
[FONT=&quot]Per ISO 11135:2007 - Medical devices containing batteries or other stored energy must be “Intrinsically Safe” as defined by the NFPA 70 standard for Class 1, Division 1, Group B hazard areas such as EO sterilization chambers.
[/FONT][FONT=&quot]

Has anyone dealt with this? Is intrinsically safe certification required? This could be tough since I think devices are typically hermetically sealed to achieve this requirement, which our product is not. We contain a 3 volt lithium battery which I think excludes us from the "simple apparatus" exclusion in the NFPA standard.

Any help is much appreciated. Glad to be on the forum.

[/FONT]
 
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M

MIREGMGR

#2
It's common to see articles in engineering publications saying that EO sterilization of lithium-battery-containing devices is OK. There must be consideration of the process effects, though, because EO can exothermally decompose even in the absence of oxygen if momentarily exposed to a hot spot. That's the reason for the "intrinsically safe" guideline one sees from the sterilization folks. They don't want their plants blown up and people killed.

Specifically, how would your device deal with the pre-humidification stage of the sterilization process, which is conducted under condensing conditions? Is your device proof against high-rate electrical discharge in the presence of a condensed water film on your circuitry and components?
 
A

arios

#3
Thank you everyone, I have gotten a lot of great information from past posts. I finally have a topic which is new thread worthy.

We manufacture a battery powered device which gets EtO exposed, and my sterilizer just brought this to my attention:
[FONT=&quot]Per ISO 11135:2007 - Medical devices containing batteries or other stored energy must be “Intrinsically Safe” as defined by the NFPA 70 standard for Class 1, Division 1, Group B hazard areas such as EO sterilization chambers.
[/FONT][FONT=&quot]

Has anyone dealt with this? Is intrinsically safe certification required? This could be tough since I think devices are typically hermetically sealed to achieve this requirement, which our product is not. We contain a 3 volt lithium battery which I think excludes us from the "simple apparatus" exclusion in the NFPA standard.

Any help is much appreciated. Glad to be on the forum.

[/FONT]
As far as I understand, one of the concerns is the risk of explosion: You are having a battery powered device [which can be a source of ignition], exposed to a flamable gas (EtO) during the sterilization cycle.

To address this issue you could have a provision in your device to prevent the chances for the unitended activation (e.g. switch moving to "on" position, or causing the circuit to work) during sterilization.
.
 
M

MIREGMGR

#4
If the battery, power switch and interconnecting circuitry were located within an intrinsically safe sub-enclosure, such a system would be EO safe.

If there's a non-zero length of conductor path exposed to the sterilization atmosphere between the battery terminals and the power switch, the presence of that power switch does not make the device intrinsically safe or condensation-short-circuit-proof.
 
G

gruhfy

#5
Thanks Guys,
The design presently has an interrupt which separates the battery from the circuit board until the user pushes the power button for the first time. This button push mechanically moves the interrupt without the user even knowing what happened inside the handle, and establishes power connection to the board. My goal was to remove the interrupt in a cost saving measure, but maybe the can of worms is bigger than the savings. If I want to remove the interrupt, does the product need to be certified as intrinsically safe? Any recommendations on a test house or applicable test standard?
 
M

MIREGMGR

#6
In my experience, usually "intrinsically safe" has a situational definition...meaning that an energy source or circuit element is either physically isolated from an environment, or physically cannot release enough energy or voltage to cause an adverse consequence in that environment.

Even when disconnected from most of a circuit, how is a battery with exposed terminals intrinsically safe and therefore suitable for EO sterilization, assuming that its energy capacity is greater than the second condition would allow? What would happen if condensation bridged the battery terminals?
 
S

Sarge

#7
The company I work for manufactures devises for use in the mining industry among others. Before they are used in subsurface mines in the US, they must to have Mine Safety and Health Administration (MSHA) approval. Part of that approval process is to submit the power source for Intrinsic Safety Testing. They look at such things as heat generation during normal operation and what happens if the battery is inadvertently shorted.

In our case we design-in circuitry to disconnect the battery in the event of excess current draw (a sophisticated fuse circuit) and encase the battery in potting compound that acts as a heat sink.

This works for MSHA but your application may be different.
 
M

MIREGMGR

#8
Does MSHA have an "intrinsically safe" definition for safety in an explosive or otherwise-exothermally-reactive atmosphere?
 
G

gruhfy

#9
Mining tools need to be intrinsically safe during operation in a potentially explosive environment. I would think that a medical device being sterilized would need to be safe in the off position, and any possible fault conditions while off. I am speculating that the device doesn't need to be intrinsically safe during operation, unless inadvertent operation is an anticipated fault.
 
M

MIREGMGR

#10
I agree that it's reasonable to stipulate that this thread's device will be "off" when it goes into sterilization, particularly given the designed battery-isolator before first intentional operation.

Maybe others have more specific device-expertise, but my EO sterilization experience is that the concern is with the potential for a battery to be shorted in the "off" state by environmental conditions at a time when the device is immersed in EO, thereby initiating an EO reaction.
 
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