Jim Choate
Plastic should burn fine, as most is polyethylene (CH2) which produces water and carbon dioxide when burned, leaving virtually no residue. The only plastic that you'd need to worry about is chlorinated stuff like PVC.
If it has any N in it then don't burn it in a closed space otherwise you will get various xCN compounds. These are very toxic, KCN is Potassium Cyanide.
As usual Jim, your posting is prolific but your science is lacking. Since N2 is highly stable, CN ions are not an energetically favored result. Some amount may be produced, but CN- is highly reactive and will quickly bind to whatever it comes in contact with (usually oxygen). The only way cyanide could escape in gaseous form is as HCN, however this cannot happen because the hydrogen has a lower activation energy for combining with oxygen, and thus the reaction is starved of free hydrogen by the time the carbon begins to burn. Various other nitrogen compounds are produced, such as NOx, but this is true of all combustion and not limited to plastic. A more likely (and deadly) result, which you did not mention, is sulfur dioxide. Most plastics don't contain sulfur, but rubber products may. Sulfur dioxide combines with water to produce H2SO3 and H2SO4 (sulfuric acid) which is quite toxic if inhaled.
When my house burned 3 years ago both my cats were killed because of smoke inhalation (approx. 9 computers and bunches of other plastics went up). It was not a pretty sight. Congealed blood from lung eruptions on their lips, very blue tinge to the skin, etc. Not a pretty sight.
Most smoke inhalation deaths result for particles clogging the lungs rather than gases. Cats have a tendency to hide when they feel threatened or injured, an instinct which often imperils them in a burning building. Also remember that computers have materials in them other than plastic, for example lead and other heavy metals. Batteries and electrolytic capacitors are also sources of many toxic materials. In short, it's not the plastic that's toxic, it's all the other crap (ink, dye, glue, solder, batteries, dielectric, etc)