I had hoped someone wouldactually look up rhubarb toxicity to mammals and humans.  In World War I, when food was short, people,especially soldiers tried eating rhubarb leaves.  That caused sickness and a number of reporteddeaths.
Rhubarb varies in itsoxalic acid concentration.  Whereas the stalks are reasonably safe to eat, theroots and leaves are considered to at times contain dangerously highconcentrations of oxalic acid.  The LD50 (median lethal dose) to rats from pure oxalic acid is about 375 mg/kg body weight.  Various reports estimate that about ¾ ounce of acid can be toxic to (143 lb) humans.  That would mean eating a few pounds of fresh leaves, but no one said one had to eat it all  in one sitting.  I suspect for the deaths, it was a cumulative dose.
Cooking the leaves withsoda can make them more poisonous by producing soluble oxalates.  The leaves are believed to also contain anadditional, unidentified toxin, which might be an anthraquinone glycoside(also known as senna glycosides). 
Admittedly, one could eat arather larger amount of rhubarb leaves without being killed, but there are along list of other symptoms that may occur at lower doses.  And, for those who question eating enoughrhubarb leaves to be at risk of death – I again remind you, there are credible reports of it happening,either due to food shortages or, I suspect, self-medication with a natural product– lots of references to rhubarb in Chinese medicine. 
From an occupational healthperspective, I found this summary:
“Effects of Overexposure toOxalic Acid:
1.      Short-termExposure:  Exposure to either solid orliquid oxalic acid can cause severe burns of the skin, eyes, and lining of therespiratory tract.  A number of deathshave occurred from swallowing oxalic acid. The symptoms appear rapidly and include shock, collapse, and convulsiveseizures.  Such cases may also havemarked kidney damage.
2.      Long-termExposure: Prolonged or repeated skin contact with oxalic acid solutions maycause pain and discoloration of the fingers. This may lead to gangrene.”

First Responders are warned to stay away from down-windexposure to oxalic.  The kicker in all of thisseems to be possible interaction with a second suspected toxin in the leavesand roots (rhizomes).  Industrial workers are warned about risks of inhaling the vapors.  Again, we all know this about oxalic, just don't forget, the primary poison in rhubarb is oxalic acid.  
Personally, I really like rhubarb in pies, as a sauce,etc.  We always had a big patch on thefarm, and we found our calves really liked the leaves.  We didn’t kill any of our calves or cows, butas the data says, people and other animals have died from eating them.  We cut a few stalks at a time, tossed theleaves over the fence, so the calves probably didn’t get enough to be aproblem.  So, I'll continue to eat rhubarb stalks, which have the lowest concentrations of oxalic acid.
As per burning rhubarb – industrial inhalation casesindicate that oxalic acid isn’t good to breath, and long-term exposure has beenassociated with lung disease.
I respectively disagree with the burning in a smoker - can’tbe any worse than anything else notion. I’ll elect not to burn dried rhubarb leaves or roots.  I'm not  going to burn oxalic acid, either as the pure substance or as a constituent of rhubarb.
My father and I made a mistake when I was in highschool.  We were cleaning up weeds in apasture near the house.  We had a 55gallon burn barrel for trash.  It wasfall, plants were frozen off, leaves and stalks dry.  We knew that there was some poison ivy in theweeds, but wore gloves.  What we didn’tthink about was inhalation of the smoke from the trash barrel fire.  
Fortunately, we were both relatively far away when wehappened to end up down wind.  Ourreactions were swift and undeniable.  Istrongly recommend, don’t breath in smoke from burning poison ivy.  We were very lucky, got out of the smokeimmediately, and the effects were fairly short-lived.  
Later, we found stories of forest fire fighting personnel, and even people burning of logs in the fireplace, where severe allergic reactions occurred upon inhalation of poison ivy, sumac, etc.  Open, raw sores in the lungs didn't sound like an experiment I want to  try.  We got away with a lot coughing; eye, skin, and some lung irritation.  Just glad neither of us was close to the barrel when the wind shifted.

 


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