Biochar safety

I've heard a few references to being careful with how you store or handle biochar.  

I'm aware that hot char straight from the stove/retort/kiln will readily ignite if it's given oxygen.  I believe if it's covered it can still give off CO or other bad gasses.

But once it's cool I've heard warnings about not storing it in piles.  Is there any truth to that?  If so, what are the general guidelines to keep from running into pesky issues like our out buildings burning down?

Thanks!

I think if you want to store large amounts of dry biochar, it make sense to have it in a separate building far enough away from anything else… just in case.
For me, most of the biochar will be used for soil building, so there is no point in keeping it dry (or in a building).

The main thing to watch out for is dust, as it's a potent explosive when it's dispersed in air: Wikipedia entry for "dust explosion"

If you're stockpiling dry biochar, keep it in closed bags or barrels and move them carefully if they are in enclosed spaces. Don't bunker the stuff. And if you fill a bin or barrel with it, remember that it's more dangerous when you've emptied the contents and there is a mix of dust and air inside.

I'm a fan of keeping it slightly damp, storing it outdoors, and getting it into applications. Non-dusty chunks are safe and I have some on my desk. They are pretty.

Gotcha...  Dust + spark = boom

So is having five chicken food sacks of the stuff sitting in the barn a risk?  I do have the bags open but there's no movement so no dust being generated or escaping.

For some reason I was thinking that I read that just having a pile of it (say a full wheelbarrow) could ignite on its own in some circumstances.  I have noticed that when I apply a bag of it to a compost pile I can hear it crinkling for a while after I dumped it out.  That made me kind of wonder...

I just keep mine mixed into compost heaps, that way it is charged and ready to go when I need it.

The only reason I can think of to store char indoors would be having a business where you are going to sell and ship non-charged char for others to make into biochar.

big piles of charcoal or true char will have a tendency to heat up and the purer the stuff is, the more likely it is to spontaneously combust.

If you have the piles out doors you will be gathering bacteria and fungi spores just by having it stored outside, and rains will keep it wetted.
Wind would also get rid of the dust created.

If the pile was big enough, and got wet or had some critter using it for a toilet, it's theoretically possible that bacterial growth could cause a build-up of heat, similar to what you'd get with damp hay. I don't know how likely that would be, and I've never heard of it happening with biochar, but theoretically it could happen.

We make it in our wood stove during the shoulder season and once it's been cooling in a metal container for 24 hours, we put it in the chicken food sacks.  I'm not building compost piles in the winter so I may have some in storage till spring.  That's where my concerns originated.

So I seems like I'm fine with my quantities and method of storage and I shouldn't worry further about it.  Thanks!!!

Mike, If you are planning to add it to compost to charge it, why not just pile it outside where the pile would be? It would be wet and cold (not very conducive to fire), and it's not like it's going anywhere...
I could see keeping charcoal dry and indoors to use as a fuel, but not for biochar for your own use.

The only stuff I keep in dry storage is mostly the portion that I intend to use in the chicken coop. I want that dry because part of its task will be absorbing moisture in the litter. It sits in chunk form in feed sacks in the carport or out in the feed shed. I only crush it when I'm ready to spread it on the litter, so I'm not keeping any appreciable amount of finely divided material in one place. Everything else lives outdoors, mostly in wool fadges, barrels where it steeps in manure slurry, or in the compost bins..all damp most of the time.

Kenneth Elwell wrote:Mike, If you are planning to add it to compost to charge it, why not just pile it outside where the pile would be? It would be wet and cold (not very conducive to fire), and it's not like it's going anywhere...
I could see keeping charcoal dry and indoors to use as a fuel, but not for biochar for your own use.

Well, I'm hoping to add it in as I build my pile in the spring.  I could just pile it there now but unless I want it at the bottom of the pile I'd have to move it again to layer it in with the compost stuff.  I could put the bags out there though...

I also have notions of making a char crusher that I'd be able to run all the char through before putting it in the pile.  I'm stomping the bags now but I figure crushing it more would probably help.

hau Mike, to crush char stored in bags I have had good success with using a sledge hammer, my pickup truck tires and a lawn roller.

Of those three the truck was the easiest and gave the best crush. I used empty hog feed bags and tied them shut with baling twine stitched through.

Cool, I've heard the truck tire method before so I'll give that a shot next time.  Better than building a machine (I hope).

Mike,
I was really into biochar. I still think its a great idea to get stable carbon into the soil. But aside from the explosive factor there are lots of volatile organic rings produced. I think it is odd that this is not discussed more, since I would in no way tolerate these compounds in my house. Aromatic rings produced during the pyrolysis are essentially quite a lot of literally benzene with substitutions. This is literally how gasoline is referred to in Europe in most places, some variant of "benzine". This was an issue in my pilot, I could smell these compounds after the quench, and there are several papers from retort operations discussing the levels in fresh char. Its really really high. This probably is OK in the retort in your stove as they burn readily when they escape the retort into an oxygen rich environment, but quite a bit remain in the char, and need to be bioremediated (I hope) before you handle or breath them.

Some will leach into the groundwater over the winter, but some microbes are capable of using them as a feedstock, especially pleurotus or oyster mushrooms which seem to be the "tiger shark of the fungi" TM. I have a settlement area downhill from my shop that probably has some oils and nasties, with a bed of wood chips with some contaminated oyster logs in there. I think that would do some good work on the carcinogens before you get exposed to them.  I didn't make char this year due to one big project which is still ongoing, but the idea is that each year I will lay a bunch of chips in the oyster bed, add char and some nitrogen and scraps, and replace annually with the remediated char being used wherever I need it.  

Hmmm, thanks TJ!  I currently make a batch in a SS steam pan with a lid in the wood stove and then swap it out with another pan when I think the first one is done cooking.  To get it out, I grab it with a pliers and carry it outside and set it on a cement stoop outside to cool.  

But in traveling across the basement it often does give off an aroma.  I'll change my process to just do one batch a day so it can cook and cook and cook and cool off in the stove before I remove it the next day.  

Tj: I think you're confusing aromatic C structures with polycyclic aromatic hydrocarbons. The C rings in biochar form between 400 and 700 degrees and are C=C bonds in complete or incomplete rings, with no hydrogen or oxygen hanging off them (the H was all driven off in the process of pyrolysis and there was no O to react with...that's why you get char instead of ash). Chemically, the carbon in biochar is graphene. If you had a process that involved high pressure as well, the aromatic ring structures would layer into crystalline sheets and you would have graphite.

If you are producing char that has a smell (tarry or smoky), is greasy to the touch, or leaves discoloration when soaked in water, your process temperature is too low (or residence time too short) and you're not driving off all the volatile compounds.

I agree with Phil.  Properly made biochar is very light, because the aromatic compounds have been burned off. You have metallic sounding, nearly only carbon, which will then have amazing amounts of surface area. It has no aroma.   Charcoal made for burning will still have wood and aromatic compounds in it. It gives off oils.  It's heavy, has an aroma and is very different than pre-char.  These are two different things, with different characteristics.  

Like many others, I am mixing compost, urine, rotten fruit, worm castings and other nutritious products in with my pre-biochar.  You couldn't light it on fire even if you tried really hard to do that.   After burning, I inoculate it this way, and then I dig it into the soil where it becomes productive.

John S
PDX OR

Amen to what John said above.  For clarity sake, charcoal becomes biochar once it's "charged" with microbial life by mixing it with compost and letting the microbes infiltrate the pore spaces.  

Unlike charcoal, biochar isn't unsafe and at risk of combustion because it's moist from the compost and mixed with non flammable decomposing/rotting plants.  Yes, charcoal must be handled and stored with care but you wouldn't be able to light biochar on fire unless it had sat out in the sun for weeks and had completely dried out. (But at that point, it really wouldn't be biochar any more, as all the microbes would have died).

And the best biochar is made from wood that has heated to the point where it no longer contains any oils or anything that would smoke if you lit it on fire again.  It should tinkle like broken glass when you run your hand through it.  It shouldn't be the least bit greasy.  If the wood is not heated hot enough for a long enough period, it won't make very good biochar.