Apart from visible damage and normal Risk Assessments specific hazards may exist from:-
Soots
Hazardous Chemicals
Soots are the result of incomplete combustion and will be a mixture of who knows what. Certainly we know that where plastic or PVC has been burnt the formation of acid from the soot is likely. Breathing in any type of soot or smoke is a health hazard. The tiny soot particles will enter your lungs and go very very deep. Don't take chances, wear a mask and ventilate your property if you can, and call for expert help, this is usually covered by your insurers.
Soot is a chemical mixture, not just carbon but the result of many chemicals burning.
Although the soots are tiny (.5 of a micron), they can have a huge surface area because of their honeycomb construction. This can hold the vapours, "odour" and chemicals. Although small amounts of contaminants are present remember (homeopathy) herbal health treatments, it is always said that Less is More!
Fire Damage
Soots penetrate almost all surfaces including hard surfaces, corrosion and staining follows.
Surfaces expand in fire scenes, pores open and soot odor, under pressure, enters. As the fire scene cools the odor pores close and the odor is locked in.
Following poor restoration the building warms up as normal living conditions resume and as the building fabric warms, pores open and soot odour returns.
Professional decontamination is necessary to prevent and avoid the latent and hidden effects of corrosion, odour and stain bleed where soots re-appear through redecorated surfaces.