Search and rescue canines can be trained to find missing persons in many different circumstances  using "Air Scent" or "Tracking" methods.  Air scent is the most common method.  The dog finds lost people by picking up traces of human scent in the air until he finds the "cone" of scent where its most concentrated.

Tracking/Trailing  dogs have their "nose to the ground" so to speak (bloodhound) as they pick up heavier particles given off by humans that fall on the ground, as a bloodhound is given an article of clothing of the missing person. The dog will track the path of the person instead of air scenting.

Disaster dogs are trained to find human scent in the aftermath of earthquakes, explosions, torndadoes and other disasters.  The dogs are trained to work on unstable surfaces and confined spaces.

Water search dogs can detect human scent in/under water. The dogs pick up the scent from bodily gasses rising up to the surface.

FEMA Canine searchers play a critical role during structural collapse incidents. The canines help search teams to locate victims, using their incredible sense of smell to detect live human scent, even from a victim buried deep in the rubble.

Each canine/handler team must pass rigorous national certification in urban search and rescue. Canine/handler teams must be re-certified at least every two years in order to participate in search and rescue operations.

For the handler, certification includes written and verbal tests regarding search-and-rescue strategies, briefing and debriefing skills, and canine handling skills.

For the search-and-rescue canine, certification includes proper command control, agility skills, barking alert skills to notify rescuers of a find, and willingness to overcome innate fears of tunnels and wobbly surfaces under the guidance of the handler.

There are two levels of certification for search-and-rescue canine/handler teams.

• Basic certification (Type 2) requires the search animal to perform to specific standards under the handler's direct supervision and guidance.
  
  
• Advanced certification (Type 1) requires the search animal to perform to those standards outside the direct supervision and guidance of the handler, and to successfully search more difficult rescue simulation courses.