According to data from the National Institute of Technology and Evaluation (NITE), it recorded 345 incidents involving air conditioners between 2021 and 2025.

Of these, more than 90% were fires that caused seven deaths and 33 injuries. Nearly half the incidents were caused by flammable objects being placed near outdoor or indoor air-conditioning units rather than due to manufacturing defects, according to Japan Times.

In 2022, an outdoor air-conditioning unit in Miyagi Prefecture caught fire after being covered with a plastic sheet and weighed down with water bottles to prevent it from being blown away by the wind. Under direct sunlight, the bottles unintentionally acted as magnifying lenses, concentrating sunlight and igniting the plastic cover.

Air-conditioner outdoor unit. Photo by Pexels

Another case in Tokyo in 2024 was traced to a user who stripped the insulation from a power cord, twisted the copper wires together, and connected them to another cable. The loose connection generated electrical sparks that started a fire.

NITE also warns against storing garbage bags, old cardboard boxes, and other combustible materials around outdoor unitssince they can easily catch fire, especially when the unit is operating.

Besides, clutter around the unit can attract animals and insects that might nest inside or damage internal wiring.

Users are advised to carry out regular maintenance and immediately switch off the circuit breaker if they notice burning smells, unusual noises, or power cords that become excessively hot.

According to the Tokyo Fire Department, blocking the airflow of an outdoor unit not only wastes electricity but can also cause the compressor to overheat, potentially leading to short circuits.

It recommends keeping the area around the outdoor unit free of combustible materials and ensuring that nothing obstructs the airflow discharged from the unit.