Which of the following is necessary before taking further action after an explosion?

Contacting local authorities is crucial before taking further action after an explosion because they are responsible for ensuring public safety, coordinating emergency responses, and managing any immediate dangers resulting from the incident. Authorities can provide critical instructions and support, including dispatching emergency services, securing the area, and evaluating the risks associated with the explosion. They are equipped to handle such emergencies and can help in assessing the situation effectively.

While gathering a team, assessing the environmental impact, and leaving the site immediately might all be relevant in specific scenarios, these actions should follow the proper establishment of communication with local authorities. The priority in emergencies is to ensure safety and engage with those trained to manage such situations effectively.