Can rocket candy explode during the preparation?

I would like to follow the steps in this video: <https://www.youtube.com/watch?v=hyPysthIRss>


After I mixed the `Potassium nitrate KNO3` and the `sugar`, I start to cook it in a pot, and stir it very often. After 25-30 min, the KNO3 and the sugar will melt together, and become a brown mass.


My question is: Can this mixture explode during the heating somehow? Or it can just burn, not explode? How to prevent it, and do it the most secure way?




See James Yawn's website [${\it Recrystalized\; Rocketry}$](http://www.jamesyawn.net/), which is all about solid propellant rocketry of the type you're interested in. It's really an exceptionally comprehensive site.



> 
> Can this mixture explode during the heating somehow?
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> 
> 


It appears that it's more likely to catch fire, and do so rather vigorously, as in cases where it's exposed to a spark or an open flame. Because the system (pan and mixture of $\ce{KNO3}$ and sugar) would be open to the atmosphere (and not confined to a fixed volume), there's more of a risk of fire than of an explosion. As reported by [James Yawn in the subsection on "Skillet Rcandy"](http://www.jamesyawn.net/skillet/large/index.html):



> 
> This stuff looks innocent enough in the pan. But if you have ever seen a quantity this size burn you will have more respect for it. This batch could send a tongue of flame 20 feet in the air and engulf the person stirring it, if only briefly. Burns to the body would likely be second degree, and I am willing to tolerate that level of risk. But eyeballs don't recover from this kind of trauma easily.
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> 
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See [this safety page from James Yawn's site](http://www.jamesyawn.net/rcandy/safety.htm).



> 
> Or it can just burn, not explode?
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> 
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Yes, it can just burn: that's essentially what's going on in the rocket engine. The exhaust from the burn is channeled in one direction (${\it via}$ the hollow core in the engine itself), resulting in thrust in the other direction.



> 
> How to prevent it, and do it the most secure way?
> 
> 
> 


From [James Yawn's site](http://www.jamesyawn.net/rcandy/safety.htm):



> 
> **Basic Safety Precautions**
> 
> 
> At present, I do NOT recommend making this propellant in a household kitchen.
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> Make small batches only! No more than one standard recipe, which yields about 160 grams of propellant.
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> 
> Wear protective gear. You should have a full-face shield, long sleeved heavy cotton shirt, heavy apron and heat-resistant gloves. These must be worn at appropriate points in the process.
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> Do not allow children or rambunctious pets in the room where you are working.
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> Do not allow distracting, inattentive, inebriated or otherwise incompetent adults in the room, especially if they smoke.
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> Be vigilant of possible sources of sparks, flame, or high temperature that could ignite propellant on contact.
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> If you smoke, place your cigarettes and lighter in another room so you will not light up unconsciously.
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> Clear your work-area of any flammable materials.
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> Have a good fire extinguisher available. Also a 5-gallon bucket of water nearby and a garden hose outside.
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> Make sure there is good ventilation, and a quick escape route to fresh air.
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> 
> Avoid stupid rocket tricks.
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> Avoid excessive exposure to Potassium Nitrate.
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> 


All of the above points are elaborated upon at the linked page.


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