From the above report:
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Officers are still unable to identify the cause of the fire, as this red-black Scania coach uses petrol as fuel, and the engine remains undamaged
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Leaving for medical treatment in another country implies the medical services are not available in Thailand. I hope TAT are taking note of this in order to adjust their medical tourism promotions.😋
Charging a lead acid battery produces flammable gas. The battery cell caps should be loosened or removed tp allow the gas to vent and prevent a buildup of pressure. Charging at too high a rate produces more gas. It is quite possible the subject battery burst its case producing the sound heard by the security guard.