Which item is commonly used to safely store partially burned papers?

Using a metal container to safely store partially burned papers is the best choice due to its fire-resistant properties. Metal containers are designed to withstand high temperatures and do not easily ignite, making them ideal for containing smoldering materials that could potentially reignite. This reduces the risk of fire spread and helps prevent accidental fires while the paper is in storage.

Other materials, such as plastic bags, cardboard boxes, and cloth pouches, are flammable and could easily catch fire from the partially burned papers, posing a serious safety hazard. Therefore, a metal container is the most secure and responsible option for safely storing such items.