Neutrons can exist in a free state.
Because neutrons have no electrical charge, free neutrons have great penetrating capabilities and are highly damaging to living tissue. This system rates the health, fire and reactivity hazards of a chemical on a scale of 0-4 where zero is no hazard and four is an extreme hazard. In addition this system notes special hazards such as acids, alkalis, corrosives, oxidizers, radioactives or water reactives. This system is commonly used on containers of chemicals or on buildings containing chemicals. Typically it is denoted by the use of a diamond that is divided into four boxes, a blue box for health hazard, a red box for fire hazard, a yellow box for reactivity, and a white box for special hazards.