PC in patient environment - BF applied part that uses USB to connect to PC

L

Luk35

#1
#1
Hello,

It is my first post and I would like to say hello to every one.

In my device I have BF applied part that uses USB to connect to PC. I will use USB isolator between applied part and PC that have 2MOPP (for signal and power). Applied part hasn't direct contact with patient skin, only trough clothes. Device can be used by active patient only. PC is used as biofeedback and patient hasn't interest to touch it. Unfortunately PC is in patient environment and as IEC60601-1 Subclause 16.1 says
within the PATIENT ENVIRONMENT, the level of safety equivalent to ME EQUIPMENT complying with this standard;
Click to expand...
Clause 16.6.1 says that between devices in ME System (within patient environment) touch current shall not exceed 100uA. In our system probability of connection accessible parts of PC to a patient directly or trough the body of the operator is negligible like clause 8.4.2 c) says. Subclause 3.8 says that
On the other hand, a part that an active PATIENT can reach out and touch might present no more RISK to that PATIENT than it presents to an OPERATOR.
Click to expand...
Can I state from this that clause 16.6.1 is not required? PC of course bears CE mark and comply 60950.
 
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L

Luk35

#3
#3
In subclause 3.8 (repeated in first paragraph in subclause 4.6) is paragraph:
A part that unintentionally comes into contact with an unconscious, anaesthetized or
incapacitated PATIENT can present the same RISKS as an APPLIED PART that necessarily has to
contact the PATIENT. On the other hand, a part that an active PATIENT can reach out and touch
might present no more RISK to that PATIENT than it presents to an OPERATOR.
Click to expand...
So IMO, active patient will be conscious, not anaesthetized or incapacitated.
 
V

VinceTech

Involved In Discussions
#5
#5
If isolated usb used, how does the touch current can exceed 100uA.

I think operator touches PC and ME Device is possible, the touch current test shall be applied. Just IMO, someone comments?
 
L

Loekje

Involved In Discussions
#6
#6
My advice: talk to your test house.

If you can make use of a USB cable of sufficient length to place the PC out of the patient environment then you may be covered already. Your test house may argue that the USB plug attached to the cable (and thus PC) can be detached without the use of a tool, so it must comply to creepage and clearance for the highest available voltage. But at Medica 2018 i've seen recently approved ME systems with a medical CE that used an ordinary USB B plug. That type of plug does not have the 3.4mm creepage required for the +5V /GND pins of which one test house says they are touchable with the (children) test finger, passing the current limits, while another test house did not mind as the current will not pass the heart but only the finger tip.

We have a very inflexible test house, so we had to incorporated a non-standard modified plug and socket to comply with under 17V-DC creepages and clearances. Maybe your design can get away with using something like a plastic Redell series plug/socket?
Also our test house would argue that if the attached PC could be inside the patient environment then this must be a medical PC as well.

Personally i'm sometimes tempted to take the shortcut when I just know something is safe but may fail if tested under surreal circumstances. Like I know that a possible voltage source of 101 milliVolt may induce more than 100uA through the measuring device, but to make a required creepage of 3.4mm for two MOPPs (CF) for this voltage is IMHO insane (especcially when this voltage is never able to directly touch a heart during surgery..).

Wishing you lots of succes,
Loek
 
V

VinceTech

Involved In Discussions
#7
#7
I will argue the connector is patient (unconscious) accessible connector. It shall be operator (or lay operator, conscious patient) accessible only. Clause 8.4.2 c) shall apply, so that the touch current testing shall be exempt.

Need expert to confirm.
 
L

Luk35

#8
#8
@Loekje in my experience with test house each of their tester has own interpretation. Technically placing PC outside patient environment is possible, but it will impact functionality. PC is for a feedback and 16 inches screen from distance above 1,6m will be unreadable and spoil the concept of the device.

VinceTech said:
If isolated usb used, how does the touch current can exceed 100uA.
Click to expand...
Touch current is measured i. a. from parts to earth (in my case from PC connector to earth thought AC adapter).

VinceTech said:
I will argue the connector is patient (unconscious) accessible connector. It shall be operator (or lay operator, conscious patient) accessible only. Clause 8.4.2 c) shall apply, so that the touch current testing shall be exempt.
Click to expand...
Clause 8.4.2 c) and subclause 4.6 is exactly that way I want to go. PC is safe to an operator and following last paragraph added in A1 of subclause 3.8: touching PC is not intended use. I am worry about clause 16.6.1... It doesn't allow exceptions like clause 8.4.2 does. On the other hand subclause 4.6 is part of annex which is purposed to clarify requirements.
 
L

Loekje

Involved In Discussions
#9
#9
Yep, 16.6.1 is something to worry about.
You can try to keep the PC out of scope, by saying that it is not a part of the medical electrical system.
As we say on Hogwarts: "Draco Dormiens Numquam Titillandus"

With risk management you can safely state that you "did not identify any risk". Then you do comply to risk management requirements and the only reproach you can get is that you did not try hard enough to identify...
But then again that reproach is only likely to happen in case of an adverse event of which you and I know is very unlikely to occur.
 
V

VinceTech

Involved In Discussions
#10
#10
In subclause 16.6, "Interconnecting cables and their connector housings are parts of the ENCLOSURE and therefore
the LEAKAGE CURRENT limits within the PATIENT ENVIRONMENT, as required in 16.6.1, are applicable."

Does this means connector pins are exempt?
 
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