Question

Are nitrates safe materials?

Answer 1

In general, I would suppose no. Fire brigades could probably point to appalling fires at fertilizer stores and ammonia factories.

Explanation:

Potassium nitrate, `KNO_3`, is a potent oxidant, although its oxidative power is often masked in aqueous solution. As a material stored in the laboratory in small quantities it is stable, and reasonably safe. It will, however, accelerate any combustion, and one of its major uses is an accelerant in tobacco (to keep your cigarette alight!); ask a cigarette smoker if it's safe.

You are also probably aware that it is a major constituent in gunpowder; as a propellant for projectiles it is undoubtedly unsafe. I am sorry if I can't give you a definitive answer; its usage determines its safety.