What should you do if you notice ice buildup on a gas cylinder?

If you notice ice buildup on a gas cylinder, it indicates that there is a potential issue such as a leak, which could lead to serious safety hazards, including the risk of an explosion or fire. Calling 911 is the appropriate action as it will ensure that professionals trained in handling hazardous materials respond to the situation. Emergency responders can assess the situation safely and implement the necessary measures to mitigate any danger.

Other options may seem less urgent but pose significant risks. Monitoring the situation without taking action could lead to an escalation of the danger. Attempting to thaw the cylinder yourself poses a risk of igniting flammable gas or creating an explosive situation, while removing the cylinder outdoors could also exacerbate the situation or create danger for others nearby. Therefore, contacting emergency services is the safest choice in this scenario.