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We are using about 10 115ah wet lead acid batteries to provide electricity for our business in the field. At night, we charge them all in the same space. The space does have a bit of airflow, but it's not like we are leaving a window open. Is charging this many batteries together in close proximity safe? I am asking due to the gases that are given off by them all while charging. Thank you for your help!

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Is it an enclosed space? Of what size? How much is "a bit of airflow?" Is there a vent or two? How big?

Lead-acid cells give off hydrogen gas when charging, which can be very explosive and even dangerous to breathe. Is there anything nearby which could spark and ignite it? (Light switch, faulty wire, sparks from grinder, etc.) They also get warm, so need some convective airflow to stay cool. Excessive heat shortens their usable service life greatly.

Essentially, if these are all crammed into a tiny space with no ventilation, then it's asking for trouble. Like this: https://www.youtube.com/watch?v=d_TnsHu2u4c

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  • \$\begingroup\$ Thanks, the video was helpful. The batteries are in a large open industrial kitchen space. So, there are no sparks flying. We are talking probably, 2k sqft of open space, with high ceilings. For ventilation, there is a nearby window that is left open some. \$\endgroup\$ – vcardillo May 15 '15 at 2:40
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    \$\begingroup\$ That sounds reasonable to me in terms of available air volume, but let me investigate. Are you using a commercial "smart" charging system? The type of charger used can have a large influence on the amount of gas evolved. IEEE 484 states “5.4 Ventilation - Maximum hydrogen evolution rate is 1.27 x 10-7 m3/s (0.000269 ft3 /min) per charging ampere per cell at 25 °C (77 °F) at standard pressure. The worst-case condition exists when forcing maximum current into a fully charged battery.” So in other words, if the charging system "floats" the batteries when charged, things will probably be ok. \$\endgroup\$ – rdtsc May 15 '15 at 3:39
  • \$\begingroup\$ Lead-Acid batteries in a kitchen??? I hope you don't have gas stoves or other open flames. To my mind, this would be a violation of all sorts of health and safety regulations. How much ventilation do you get from a window that is "left open some"? I think the batteries should be sealed off from the kitchen, and the battery compartment should have forced ventilation to the outdoors. \$\endgroup\$ – Peter Bennett May 15 '15 at 3:47
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    \$\begingroup\$ However, hydrogen is flammable/explosive in concentrations from 4-74% in air. If we said the ceiling was 12ft and the area 2k sqft, that's a volume of 24k cuft. 4% of that is 960 cuft. So if more than this much gas is produced overnight in a sealed room, things start getting dangerous. \$\endgroup\$ – rdtsc May 15 '15 at 3:50
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    \$\begingroup\$ Using IEEE 484, if there were 10 cells in each battery, and the charger gave an overnight average current of 1 ampere per cell, then each battery could release 10 x 0.000269 ft3 /min = 0.00269 ft3/min X 60s = 0.1614 ft3/hr x 8 hours = 1.3 ft3/night x 10 batteries = 13 cuft for all of them overnight. Of 24k cuft, 13 cuft is (13/24000*100) = 0.054%. However if it was a 100 ampere constant voltage "dumb" charger, you'd be at 5.4%, and the entire room could explode when someone flipped the light switch... \$\endgroup\$ – rdtsc May 15 '15 at 4:10
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The regulations that apply to this scenario will vary from one country to another, and from one scenario to another (domestic, commercial, industrial). I strongly recommend you find out what applies in your location & situation.

Forced air extraction AT THE ROOF LEVEL is highly recommended, as lead-acid batteries WILL vent significant amounts of H2 (qty depends on many factors), and it will pool at ceiling level & work downwards, displacing ordinary air. Concentrations of as little as a few percent become explosive.

As @rtdsc said, how much H2 depends on many variables, including charge profile, battery types, temperature, etc. Also an acid-resistant 'drip tray' for all the batteries to sit in would be a good idea.

The proximity of the batteries to each other isn't so much of an issue from a H2 gas perspective, but it can be in terms of cooling - lead-acid doesn't like heat, & giving them as much space between them (i.e. a few inches) is ideal.

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Normal safe handling rules are more important for the situation as described: Charging Lead-Acid batteries. If you require mechanical ventilation, you should also install a hydrogen level alarm.

Typical standards require hydrogen concentration less than 1-2%: On the description you've given, that would require a complete air change every week or so, and you probably have a complete air change several times an hour.ventilation requirment guesser

Note: Hydrogen is flammable, but difficult to ignite, at 4%. Explosive at 18% safety sheet

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