According to the NFPA system, what does a red square labeled '1' indicate regarding flammability?

In the NFPA (National Fire Protection Association) labeling system, a red square labeled '1' indicates that a substance must be preheated before it can ignite. This classification portrays a specific level of flammability risk associated with materials. A label of '1' signifies that while the material is flammable, it has a higher ignition point and requires additional heat to initiate combustion.

Understanding this classification is vital for safety in environments where flammable gases are present, as it helps determine the appropriate precautions during handling, storage, and usage of such materials. Proper awareness of these ratings contributes to the prevention of accidents and enhances overall laboratory safety. In contrast, designations for '0', '2', and '3' reflect no flammability, moderate flammability, and fire risk at normal temperatures, respectively, thus providing a clear hierarchy of flammability hazards for safety planning and training purposes.