Maximum temperature during normal use - non-skin contact

[Avidan B]

Hi, my 2 cents:
1. medical gloves are not a thermal isolation means
2. as you wrote, the ambient temperature in OR are controlled (20-25degC)
3. find a reference from other standard like IEC 80601-2-60 (dental equipment):

 

[jddad19]

I think the use of the gloves to avoid Table 23 is itself not relevant, since presumedly the gloves are fairly thin and wouldn't reduce the temperature significantly. But it could be worth a shot (to get around Table 23) as long as if the actual temperatures are anyhow safe.

In my opinion (of course, it might not count!) the use of an object to simulate the thermal loading of hand is not outside of the standard, as it's incorporated in the first line of Clause 11.1.1, compliance is tested "When ME EQUIPMENT is operated in worst-case NORMAL USE ... ". While Clause 11.1.3 a) 3) does refer to putting a hand held device in still air, this clause (title: positioning) should itself not create an abnormal test condition. But, there is the side issue that 48C seems high for a part that must be held by the operator, especially if it is more than 10min, but it gets complicated as the wrong ambient is used. So the 48C might be itself a massaged messed up limit based on open air test.

As a side note: the standard IEC 60601-2-37 for ultrasounds is a good reference, as it has good methods and limits for the ultrasound probes which can get warm and need to contact the patient. I just check and found for skin contact it uses 33C (not 35C) and has a limit of 43C, which means an effective 10K rise for skin contact, when tested with material mimicking tissue for thermal properties. It also has a separate test in still air which allows up to 27K rise (50C in 23C ambient).

Anyway, step one for dealing with a test lab is to have your own data or plausible rational to show that it is safe with good design margins. It could be cooling by the body, it could be short usage time, it could be that the gloves are somehow really reducing the temperature. Then show this to the lab in advance of the test. If necessary document it in risk management. A good lab should be able to appreciate the effort and work with it.

Thanks so much for your input and insight, really appreciate it.

 

[jddad19]

Hi, my 2 cents:
1. medical gloves are not a thermal isolation means
2. as you wrote, the ambient temperature in OR are controlled (20-25degC)
3. find a reference from other standard like IEC 80601-2-60 (dental equipment):
View attachment 30897

That's an interesting thought. Assuming I'm reading the note correctly though I think that means those limits apply for up to 10s intended contact, which would align with the 60601-1 standard (Table 23). Do you know if the 80601-2-60 standard provides a different limit for prolonged contact (>1min) on the operator side? I don't have the standard myself but will purchase it if the reference proves helpful.

 

[Peter Selvey]

It looks like the limits in IEC 80601-2-60 are based on the operator's "reaction time" (per Note "a" in the table), In other words, 56°C would be uncomfortable and potentially dangerous with time but the operator can just put the tool down before they get a burn. The back story here is that typically the heat source is the motor which is normally designed for intermittent use. So for example a motor might be specified as 10s on 20s off (1/3 duty cycle) and could reach temperatures of 50C or more if tested continuously under a 1/3 duty cycle. But in practice the tool would not be used that way, and everyday temperatures would be fairly low. So in truth a duty cycle like 1/3 is is really a quasi-abnormal condition, with an inherent risk control measure based on the operator putting the tool down if it feels too hot.

By "quasi-abnormal condition" I mean something that occurs occasionally during the lifetime of the device. It shouldn't cause any significant harm, but it might interrupt a procedure. A common example might be a low battery, filters getting blocked, user miss, getting wet, and in this case, things getting used at a high duty cycle. IEC 60601-1 doesn't really have a category for this, only "normal condition" and "abnormal condition" and latter is really for rare things like component faults. Often these quasi-abnormals are lumped in with normal condition, which then requires a fudge on the criteria, such as -2-60 allowance for 56°C in "normal condition".

 

[Avidan B]

That's an interesting thought. Assuming I'm reading the note correctly though I think that means those limits apply for up to 10s intended contact, which would align with the 60601-1 standard (Table 23). Do you know if the 80601-2-60 standard provides a different limit for prolonged contact (>1min) on the operator side? I don't have the standard myself but will purchase it if the reference proves helpful.

Hi,
That's the whole refence for the max temp. of operator side taken from the Dental equipment particular st.
Re. the 10s, why do you need a longer contact time?!
Since the operator consider to be fully conscious (hopefully ), a normal reaction time in case of over heat of 10s is acceptable.
I recommend rationalizing all of this in your risk file (and add a reference to IEC 80601-2-60 cl. 201.11.1.1).
Avidan

 

[Tidge]

I don't want to chime in on the temperatures (I think this was well-covered earlier in the thread) but I wanted to agree that the risk management file really ought to have all this documented, and be in alignment with the final certification tests.

As for "10 seconds" (maximum length of time to cause injury), this reminds me very much like the "immediate" category for onset of potential harm from 60601-1-8.

 

[jddad19]

Hi,
That's the whole refence for the max temp. of operator side taken from the Dental equipment particular st.
Re. the 10s, why do you need a longer contact time?!
Since the operator consider to be fully conscious (hopefully ), a normal reaction time in case of over heat of 10s is acceptable.
I recommend rationalizing all of this in your risk file (and add a reference to IEC 80601-2-60 cl. 201.11.1.1).
Avidan

In our case the operator would need to handle the device for an extended period of time (>1min and likely >30min in practice) to delivery therapy so it would render the device useless if we can't design the device to meet acceptable touch temperature limits for prolonged use.

All in all, I think the conclusion is that we should stick to the limits defined in 60601-1 regardless of the fact that the device is not touching "bare skin", but that we should consider normal use with a body (or surrogate) pulling heat from the device in the test method for measuring heat as opposed to the "in air" method only. And of course document all of this in our risk management file.

Thank you everyone for you inputs!