Different metals require different temperatures to melt. The one thing they all have in common is the melting temperature is hot enough to cause serious injury in a mishap.
Your best safety tool is your brain.
Clothing and Safety Gear
Wear protective clothing and devices like safety glasses and full face sheilds.
Cloths made of natural fibers like cotton are to be prefered over synthetics that can melt.(and melt to you)
Shoes or Boots. Leather boots recomended, alum will only loose 10 or 20 degrees of its 1400 as it melts through your nylon tennis shoes and embeds in your feet....
If your metal requires it (like iron), wear eye protection against the bright glow produced.
Generally, clothing and gear for welding is a good choice for aluminum foundry work.
High top boots without laces, with pant legs pulled down over the tops of the boots so no stray metal can get in the boots.
Imagine a crucible failure at any time and be aware of what will happen. Use this knowledge to modify what you are doing to prevent a problem.
Work over dry sand, if possible, to contain any spills. Never work over concrete, as a spill will cause the concrete to spall (explode).
Think fire safety, if you do something bad that flings hot stuff all over, where will it land, and will it catch fire, how will you put it out...
Proper ventilation, working outdoors is best. Try to work so the fumes are blown away from you. Breating the smoke is bad, especially in lost foam casting.
General work habits
Preheat ladles, scrap to be melted to make sure it is dry to prevent moisture (steam) explosions.
Never put water on hot/molten metal. throw sand on it if you must.
Molten metal will ignite most anything combustible in a spill. Plan ahead for a fire and what to do about it.
Most fires will be small and contained. A mold may flame up when poured and a plastic bucket used to house sand and a foam pattern for lost foam casting will be lost to fire the first time it catches a spill.
NEVER USE WATER to douse a fire in the foundry area! Water introduced to melting temperatures will cause a steam EXPLOSION. This is no exageration, it will literally expand to steam in an instant and burn you and fling things like drops of molten metal in every direction.
Fire in a foundry is best left alone if contained or doused with sand to smother flames that are in danger of spreading.
If you have any other safety issues, please add to this.