Polymer Lithium Ion Battery and Ventilation Requirements

#1
Dear all

We have a Medical equipment with Ip clasification IPX4 than supplied from a polymer lithium ion battery with capacity up to 1000 mAhr.
The battery is in separate container in the case of the device.
IEC 60601-1 ed 3.1 in clause 15.4.3.1 refer the need of ventilation of this container in order to protect from accumulation of gases and possible ignition.

Is it necessery to ventilate the container for these types of small batteries ?
 
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Ninja

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#2
Re: Polymer lithium ion battery and ventilation

Caveat: I am not in medical or medical regulation...I'm just familiar with the batteries.

I would expect ventilation of the battery in any high load, high risk or extended use application. The batteries are way cool, and very effective, but can and do self ignite on avalanche discharge.

It may never happen, or it may, depending on the particular battery. {Not the particular battery design...the particular battery itself}.
The hotter the battery is, the higher the probability of unwanted discharge (read "short"). Should this happen, there is a bit of nasty off-gassing. If the gas is trapped either within the battery or within the enclosure, you can have a pressure effect (read "spray molten plastic parts all over the room").

Not helpful with your question regarding requirements, but hopefully helpful in some other way.
 

Mikishots

Trusted Information Resource
#3
The intent of the ventilation is to mitigate bursting of the battery container in the event of a malfunction of the battery. Any rechargeable battery can vent (during normal operation or malfunction), and the clause would apply to all of them. I would find it highly improbable that any medical device with a sealed battery compartment for rechargeables would be certified.
 
Last edited:

Peter Selvey

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#4
We need a real battery expert here, but just from my research I would disagree with the focus on fault conditions.

The specific clause refers to accumulation of gases during charging or discharging, so this implies consideration for normal condition, not sudden gases from venting under failure conditions.

Some types of cells create gases in normal charging, e.g lead acid creates hydrogen. Hydrogen is flammable, so venting is an important consideration.

Most of the modern cells (Li-ion, NiMH etc) are sealed so the only venting occurs in fault condition, which is a rare event.

If a Li-ion cell does reach the point of venting, it is likely to be severely damaged and already reaching the point of ignition (chemical fire). Literature indicates that the vented gases may be flammable, increasing the intensity of the fire. However, at this point, ventilation in the equipment is not going to make much difference. Actually it could make it worse, due to the supply of oxygen.

So I really think the clause is talking about normal condition, gases from charging and discharging.
 
#5
It may be worth bearing in mind that there is some changes to the battery clause brought in by Amendment 1.

So Amd. 1 15.4.3 states:
In ME EQUIPMENT, housings containing batteries from which gases can escape during charging or discharging shall be ventilated so that there is no unacceptable RISK from the accumulation of gasses and possible ignition is prevented.
Battery compartments of ME EQUIPMENT shall be designed to prevent accidental short circuiting of the battery where such short circuits could result in the HAZARDOUS SITUATIONS described in 13.1.
(Clause 13.1 is the list of fault conditions to consider).
 

Ninja

Looking for Reality
Staff member
Super Moderator
#6
...In ME EQUIPMENT, housings containing batteries from which gases can escape during charging or discharging shall be ventilated ...

Just thinking out loud here, with the same caveat as above:
Are there any batteries from which gases CAN'T escape during charging or discharging?

"Can" is such a loose word that it seems that the requirement is up to the mood of the auditor. Gases "can" escape from a block of granite in my garage...it just isn't likely to be much...

hmmmppphh.
 

Mikishots

Trusted Information Resource
#7
We need a real battery expert here, but just from my research I would disagree with the focus on fault conditions.

The specific clause refers to accumulation of gases during charging or discharging, so this implies consideration for normal condition, not sudden gases from venting under failure conditions.

Some types of cells create gases in normal charging, e.g lead acid creates hydrogen. Hydrogen is flammable, so venting is an important consideration.

Most of the modern cells (Li-ion, NiMH etc) are sealed so the only venting occurs in fault condition, which is a rare event.

If a Li-ion cell does reach the point of venting, it is likely to be severely damaged and already reaching the point of ignition (chemical fire). Literature indicates that the vented gases may be flammable, increasing the intensity of the fire. However, at this point, ventilation in the equipment is not going to make much difference. Actually it could make it worse, due to the supply of oxygen.

So I really think the clause is talking about normal condition, gases from charging and discharging.

I strongly disagree. The word "accumulation" is carefully chosen; it applies to ANY condition, whether it be from normal use, elevated temperatures or a failure of some kind. And just because Li-Ion batteries are venting does not mean that they are severely damaged or already reaching the point of ignition; that statement is opinion at most.

I have worked with primary and secondary battery chemistries and systems for 15+ years, including TUV certifications for battery powered solar systems and charging devices.
 

Peter Selvey

Staff member
Super Moderator
#8
This is a classic case where modern approach to risk falls down. Agencies like the TUVs scream that IT'S DANGEROUS, but then they turn around and accept weak risk controls like a few ventilation holes in the bottom of the enclosure.

What we would see under ISO 14971 would be something like this:

Hazardous situation: accumulation of gases from batteries, leading to explosion
Risk estimation: unacceptable
Risk control: ventilation
Residual risk: acceptable

What is missing is detail on the characteristics of the situation. In the first place, we need to know the types of gases, the quantities and rates under various conditions (normal, defective, severely damaged), the potential to be ignited and so on.

If that turns out to be significant (which I still have doubts), we then need to switch focus to the details of the risk control: ventilation - how many exchanges of air can we expect per hour, how does that match to the characteristics of the original hazard? Do we need forced ventilation? Do we need verification tests? What happens when the equipment is turned off or the fan stops? And so on.

I can accept that it could be a significant risk, but if so, we need some solid details. If the details are hard to find, and it is a common issue (as this one is) it's a good indicator the risk was never that significant in the first place.
 

Mikishots

Trusted Information Resource
#9
This is a classic case where modern approach to risk falls down. Agencies like the TUVs scream that IT'S DANGEROUS, but then they turn around and accept weak risk controls like a few ventilation holes in the bottom of the enclosure.

What we would see under ISO 14971 would be something like this:

Hazardous situation: accumulation of gases from batteries, leading to explosion
Risk estimation: unacceptable
Risk control: ventilation
Residual risk: acceptable

What is missing is detail on the characteristics of the situation. In the first place, we need to know the types of gases, the quantities and rates under various conditions (normal, defective, severely damaged), the potential to be ignited and so on.

If that turns out to be significant (which I still have doubts), we then need to switch focus to the details of the risk control: ventilation - how many exchanges of air can we expect per hour, how does that match to the characteristics of the original hazard? Do we need forced ventilation? Do we need verification tests? What happens when the equipment is turned off or the fan stops? And so on.

I can accept that it could be a significant risk, but if so, we need some solid details. If the details are hard to find, and it is a common issue (as this one is) it's a good indicator the risk was never that significant in the first place.
To be clear, it's not the danger of fire that's in question - a fire would be a result of an ignition event. The intent of the ventilation detailed is to prevent the situation of an enclosed/sealed compartment that can burst, and this bursting would certainly not be restricted to ignition as a cause.

If a battery is having an issue, vents hydrogen and then subsequently is ignited by some source, so be it; the ventilation requirement will not prevent or mitigate this because these events are wholly independent of the requirement. What it will mitigate is the risk of the battery's compartment (presumed to be part of the medical device) bursting. Fires have the possibility of being managed, but bursting due to a pressure rupture happens too fast and is over in a fraction of a second; the damage is done.
 
Last edited:

Peter Selvey

Staff member
Super Moderator
#10
The standard specifically refers to accumulation and ignition, so it is fire that is the point.

The bursting of a sealed battery compartment is theoretical but unlikely to be an issue; most battery packs in medical devices are small compared to the volume of the enclosure so the increase in pressure from venting would not be significant; and an IPX4 enclosure would be unlikely to be tightly sealed to withstand a large amount of pressure.

This is a very old requirement (more than 25 years old), and written at a time when lead acid batteries would have been popular. The risk for lead acid batteries is well documented in literature, you can find many references to accumulation and ignition - exactly what the clause is referring to.

But I cannot find any literature indicating the same problem for modern batteries like Li-ion and NiMH. In fact I found one article that specifically states Li-ion does not require ventilation. For the recent fire problems for Boeing, ventilation is mentioned as an issue, but the literature states this is for temperature, not accumulation of gasses. These are large packs and were probably overheating.

For reference. Li-ion cells have three protection devices: a PTC device to limit current, a pressure operated CID (current interrupt device), and finally a safety vent. Since the CID is a pressure switch, for it to work the cell must have a intact sealed enclosure. The safety venting is a last resort. This implies that venting from Li-ion is a rare event.
 
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