Lithium Ion Batteries Exhaust Ventilation

[sider]

Does anybody have experience with the design of exhaust ventilation for off-gas event for lithium-ion batteries?

I have a few questions regarding FM Loss Prevention Data Sheets and NFPA 855.

1. In NFPA 855 4.9.3, the mechanical ventilation rate is defined to be not less than 5.1 l/s/m2. Could somebody clarify the logic behind this? This rate apparently depends on the area of the room, and it would be the same for a small room with x amount of batteries and a big room with a similar x amount of batteries, however, the exhaust rate would be different, so I am not sure how to approach this.
2. NFPA 855 states that if not continuous, the ventilation should be triggered on 25% LFL. Does that LFL refer to CO, since that gas is consistent in the whole process?
3. If the exhaust ventilation is turned on, and off-gas products are taken out of the building, is it necessary to have a supply fan on in order to further lower the percentage of explosive gasses in the enclosure?
4. Is there any requirement for fans to have ATEX? I understand that if we keep below LFL there is no explosive atmosphere, but would also like to clarify this.
5. NFPA 855 states that at least a minimum of 2 hours of standby power is needed. Do you usually connect explosive gas detectors which start the exhaust fans to the same standby power source?

 

[3DDave]

Are you sure that li-ion out-gas/off-gas? Liquid lead acid batteries electrolyze hydrogen and oxygen when over charged.

Li-ion tend to explode and burn when over charged. AFAIK they don't produce hydrogen.

 

[HVAC-Novice]

i didn't look up NFPA 855... but are you sure they talk about CO, as in carbon monoxide?

if hydrogen is a concern (i don't see how that is in Li-ion), also refer to NEC since that has had lead acid battery room requirements for a long time (to prevent H2 creeping into conduit etc.)

 

[nuuvox000]

1. That sounds like it's just prescriptive code you need to follow. Based on historical data and battery charging theory, I would imagine.
2. As far as I know, hydrogen is the gas that code is worried about. Very explosive.
3. If a certain volume of air is exhaust, it has to be made up somehow; either by infiltration, relief damper, or supply fan.
4. Not sure what ATEX is, but is it referring to an explosion-proof motor? My code (IMC) doesn't require it but I usually specify it just for good measure. If you don't want an explosion proof motor, I typically make sure the motor is outside of the airstream.
5. I would think you would have to, otherwise there's no point in the fans being powered. Either that, or set the fans to run if there's a power interruption which seems like a waste of energy.

Also, from what I understand, lead-acid batteries are the batteries that give off hydrogen, not lithium-ion. However, in my code there is no distinction made so we have to provide ventilation for both.

 

[sider]

Li-ion tend to explode and burn when overcharged. AFAIK they don't produce hydrogen.

Yes, but before burning and exploding, the batteries go to thermal runaway and produce explosive gasses (hydrogen, carbon monoxide, etc.) which could be vented to ensure the LFL is below so there is no explosion.

I didn't look up NFPA 855... but are you sure they talk about CO, as in carbon monoxide?

I have read that during thermally runaway both hydrogen (LFL 4%) and carbon monoxide (LFL 12,5%) are released, however, CO starts first to appear so my thought was maybe to measure it first?! But as I said, this ventilation should address the issue of the off-gas event, which only happens when the battery goes into thermal runaway (not normal state), while during the normal operation I don't see the need for ventilation since batteries during charge and discharge don't produce any gasses.

1. That sounds like it's just prescriptive code you need to follow. Based on historical data and battery charging theory, I would imagine.
2. As far as I know, hydrogen is the gas that code is worried about. Very explosive.
3. If a certain volume of air is exhaust, it has to be made up somehow; either by infiltration, relief damper, or supply fan.
4. Not sure what ATEX is, but is it referring to an explosion-proof motor? My code (IMC) doesn't require it but I usually specify it just for good measure. If you don't want an explosion proof motor, I typically make sure the motor is outside of the airstream.
5. I would think you would have to, otherwise there's no point in the fans being powered. Either that, or set the fans to run if there's a power interruption which seems like a waste of energy.

1. It is still unclear to me which code even addresses this issue, since in NFPA required quantity is mentioned for ventilation and I think they meant it for continuous ventilation in the case of VRLA batteries (they also state lithium-ion doesn't need ventilation), however in FM Guide the same ventilation rate is mentioned for ventilation of lithium-ion during off-gassing. Seems a little weird to me.
2. I understand since it has lower LFL, but on the other hand CO is also produced during off-gas with an LFL of 12,5% and if it vents first maybe the explosive atmosphere would be reached first under its influence?
3. I see, so the supply air fan makes sense. I assume it would be wise to ensure that there is certainly under pressure in this event in the building, supply air amount slightly lower than exhaust?
4. Get it. My concern is that the fan is located in the room, and the motor would be inside the atmosphere.
5. My thinking also.

Also, from what I understand, lead-acid batteries are the batteries that give off hydrogen, not lithium-ion. However, in my code, there is no distinction made so we have to provide ventilation for both.

You are right, but as I stated earlier in the post, this ventilation would not work during the usual operation of the batteries. It would only work in the case when there is an imminent thermal runaway and the battery starts to dissolve and vent out with explosive gasses and fill the room with it.

 

[nuuvox000]

The code you have to follow is whichever one the AHJ knows about and requires; it could be any or all of them. Frustrating but true.
I haven't heard about CO off-gassing, but if you're right about that then yeah, you'll have to provide exhaust and detection for that as well.
Yes, I would definitely keep the room under negative pressure.
I would get an explosion proof fan with a non-sparking blades in the airstream (I think they use aluminum or a plastic).

 

[chicopee]

The NFPA has values for lower explosive limits for flammable gases and the American Conference of Governmental Industrial Hygienists have values for permissible concentration limits for work environments for explosive and toxic gases. OSHA has also its own values which may or may not correspond to the NFPA and the ACGIH. Use the most stringent values from these three entities. So you have to know the generation rate of such gases, the size (volume) of the room where such gases is generated and calculate the flow rate of make up air to maintain the concentrations with the limits established by either of these three entities.