What action should be taken if ice buildup occurs on the gas cylinder?

When ice buildup occurs on a gas cylinder, the appropriate action is to ensure the safety of the situation first. The correct answer involves assessing the immediate risks associated with the ice buildup, which can indicate a possible leak or other safety hazard. Calling 911 is critical in ensuring that professional responders can assess the situation and mitigate any potential dangers. This action ensures the safety of those in the vicinity.

Other actions, such as removing the cylinder from service, while prudent, may not be sufficient in emergencies where immediate professional help is necessary. Thawing the cylinder with hot water or waiting for it to melt naturally could lead to unsafe conditions, including the risk of an explosion or toxic gas release, depending on the type of gas involved. Therefore, contacting emergency services is a proactive and responsible response to such a hazardous situation.