Fifteen thousand Shell liquefied petroleum gas (LPG) cylinders were recalled in August last year after a domestic cylinder exploded, killing an elderly woman in a squatter hut in July, an inquest heard yesterday. Engineers from the Electrical and Mechanical Services Department called in to investigate the fatal blaze in Wong Tai Sin on July 3 had noticed a possible defect in the regulator - a device which connects the cylinder with the stove and controls flow and pressure. Reports from the Japanese maker confirmed 15,000 regulators, in two batches produced in September 1995 and March 1996, could have weak screws which could leak and explode under pressure. Shell Hong Kong made a recall appeal on the potentially hazardous cylinders on August 13. Yesterday its representative admitted that about 2,000 of these suspect LPG cylinders had not yet been returned by householders. But public affairs manager Irene Chan Man-tuen said there was only a slim chance that any were still in use. 'Users have to replace a gas cylinder every several months. When our agents are called in to change it they know immediately if it belongs to these batches. 'We believe the households have either changed to other suppliers or the cylinders have been dumped.' A tenant at the Chuk Yuen United Village, Wu Tak-ping, said he heard the sound of leaking gas when he switched on the regulator on July 3. He tried to switch the supply off but gas kept leaking. Mr Wu rushed out to alert villagers. Shortly after he returned home and turned off the electricity, the cylinder exploded and caught fire. Mr Wu managed to escape. Chan Fung-kin, 79, was found buried under debris in her neighbour's house, where she was believed to have taken refuge. She was badly burned and had died from smoke inhalation. Coroner David Thomas recorded a verdict of accidental death. Electrical and Mechanical Services Department engineer Jimmy Yeung Tat-wing said the regulator used by Mr Wu belonged to the batch made in September 1995. Investigations concluded the defective regulator leaked gas and the explosion was caused when the gas-filled air was ignited by fumes coming from a kerosene stove. Shell suggested the regulator did not leak but was damaged in a fire started by the stove and subsequently led to an explosion. But university tests showed regulators did not melt even when exposed to high temperatures.