A burning battery pack led to a plane with more than 200 people on board making an emergency landing. 

The SriLankan Airlines Airbus was flying from Kochi in India to Colombo in Sri Lanka and was just starting its descent to landing when spoke was spotted coming from an overhead locker. 

The pilot declared an emergency while the cabin crew opened the locker and found a bag which was the source of the smoke. 

They used fire extinguishers to douse the fire and discovered the cause to be a battery pack which they then put into a water-filled container to cool it down. 

The aircraft landed safely at Colombo. 

Special fire-retardant bags called AvSax specifically designed to deal with fires in electronic devices are now on board several major US carriers.

The AvSax is used when lithium-ion batteries in mobile phones or other electronic devices catch fire.

Simply pour at least two litres of water into an AvSax and then drop the burning device into the bag. The water activates the polymer gel inside the bag causing it to expand around the device. Should the device keep on venting then the AvSax is tough enough to absorb the force.

In short, the AvSax cools the batteries in the device, reducing the likelihood of the battery catching fire but if it does go into what is known as thermal runaway it is all contained within the bag.