The Electrical and Mechanical Services Department (EMSD) has completed the investigation into the Ocean Park's helium balloon ride incident on June 28 and released the findings today (August 30).
In the course of the investigation, the EMSD inspected the operation logs and maintenance records, studied the CCTV records and interviewed the relevant staff of the Ocean Park and the injured persons in order to determine the circumstances of the incident. The EMSD later carried out detailed inspection of the balloon components such as the balloon envelope and the rip panel (see Annex 1). The EMSD engaged a material expert to further examine the balloon components and to prepare for laboratory testing of the tensile strength for 26 samples under different temperatures and conditions. The material expert also provided professional advice for the investigation.
Based on the data gathered and the interview records, the pressure of the helium gas inside the balloon dropped when the balloon was about 60 metres above ground. The balloon started to descend at accelerating speed due to insufficient buoyancy when it reached about 20 metres above ground.
Upon thorough inspection an opening was found at the rip panel joint. There was also local detachment at the covering strips at the joint. The rip panel is located near the top of the balloon (see Annex 1) and is used for quick deflation of the balloon at the ground in the case of an emergency, like a typhoon, to avoid creation of a hazard. The joint between the rip panel and the balloon envelope was sealed by covering strips, and bonded with specific cement.
In summing up the results of the inspection and tensile testing, the EMSD came to believe that the thermal and mechanical cycling effects of the balloon during operation had reduced the adhesion of the covering strips, and caused the formation of local detachments (see Annex 2). The tensile strength of the joint was thereby weakened. These detachments could be extended upon further operation cycles, resulting in splitting at the joint. As a result, helium gas leaked from the opening and caused this incident. The Ocean Park previously identified and rectified local detachments formed at the corner of the covering strip during periodic inspection; however, any detachment formed in the central part of the covering strip would be rather difficult to detect during periodic inspections.
After the incident, the EMSD issued a closure order directing the Ocean Park to stop the operation of the balloon. To prevent similar incidents, the EMSD has requested the Ocean Park and the balloon manufacturer to work out a comprehensive method to inspect the rip panel joint. The EMSD will consider allowing the resumption of operation of the balloon only when the effectiveness of the improvement measures is confirmed.
The investigation report is available at the EMSD's website (www.emsd.gov.hk/emsd/e_download/pps/amr/Incident_Report.pdf).
Ends/Thursday, August 30, 2012
Issued at HKT 15:59