The primary concern is that the fuel cells burn with an open flame which keeps the lantern afloat for several minutes. Technically the device should only fall to the ground when the flame is out but if a lantern is caught on a tree or building, there is a significant fire hazard. The paper that makes up the outer part of the lantern is flammable and if the lantern is out of balance, the entire lantern can catch light.
The list of safety instructions includes:-
Do not release any lanterns within a 10km radius of an airport or landing strip.
The flight path of the lanterns should avoid buildings and trees.
Do not release lanterns in winds stronger than 8km/hour.
Do not light lanterns within or close to dry crop fields and thatched roofed properties.
Do not launch lanterns in areas that are prone to veld fires.
Never light lanterns whilst under the influence of alcohol or drugs.
Never smoke whilst handling the lanterns.
Ensure that all young children are kept under supervision and away from the source of ignition during the release.
If possible, wear protective clothing when lighting the lanterns
Make sure you have water and/or fire extinguishers at hand.
Inform the Aviation Authorities if you are going to launch sky lanterns in large numbers.
As they use an open flame, they may not be used at specified times in certain parts of our country such as on Guy Fawkes Day (5 November) which falls within the fire season in the Western Cape and is often subject to fire bans in this period.
The assessment included actual testing of three sky lanterns. The results were identical. A safety observation was that hot fuel drips once lit and we experienced an injury from this. This presents potential problems for humans and animals alike.
Even if all the safety precautions are followed, the wire framing presents potential problems for animals and the environment if not collected after use. Realistically, the likelihood of collection would be low if the lanterns are released on windy days where they can travel long distances before settling on the ground. As they are burned at night, keeping track of the lanterns to collect the wires present logistical problems.
Sky Lanterns have been banned in Vietnam, Australia, Austria, parts of China, Thailand and Germany. Serious concerns have been expressed over the impact of sky lanterns on aviation safety. The UK Coast Guard has expressed concern over how they can mimic distress flares and farmers and welfare groups around the world have expressed opposition due to the wire structures and the potential for ingestion and other injury by animals.
As with any product, if used responsibly and the wire framework is collected after use, the lanterns provide a visually pleasing display of light, without the resulting noise and trauma to animals.