What are the consequences of of nasogastric tubing in wrong place?

Serious to deadly. If you route the NG tube incorrectly, esophageal perforations, pneumonitis, pulmonary hemorrhage and pneumothorax are all possiblities, and all of these can have a fatal outcome. The best way of checking placement is an xray. Clearly this is impractical at an emergency scene. Instead, check the aspirate for pH and and look at it -- see if it looks like gastric contents. pH, while usually effective, is fallible in cases where the patient has an unusual gastric pH (GERD for one obvious example). Normal pH for gastric is 1 to 4 -- it'll be higher if you've missed and gotten into the lungs or the small intenstine. Gastric aspirate will usually be clear or light yellow, but if there's a GI bleed, expect blood tones (black and tarry, "coffee grounds", etc.). I know about dipping the tube into water and watching for bubbles, listening, etc. but most of these methods turn out to be inconclusive.