Final answer:
The second safety rule of handling a weapon in a lab is to know the locations and proper use of specific safety equipment such as fire extinguishers and eyewash stations.
Step-by-step explanation:
The second safety rule of handling a weapon, particularly in the context of a laboratory setting where different types of equipment and chemicals can be seen as 'weapons', is to know where specific safety equipment is located. This includes being able to quickly locate and use fire extinguishers, eyewash stations, and any other relevant safety apparatus in case of an emergency. It is imperative that one not only knows the location of these tools but also how to use them properly to ensure the safety of oneself and others around.