 Although ytterbium is fairly stable chemically , it is stored in airtight containers and in an inert atmosphere such as a nitrogen @-@ filled dry box to protect the metal from air and moisture . All compounds of ytterbium are treated as highly toxic , although initial studies appear to indicate that the danger is minimal . Ytterbium compounds are , however , known to cause irritation to the human skin and eyes , and some might be teratogenic . Metallic ytterbium dust can spontaneously combust , and the resulting fumes are hazardous . Ytterbium fires cannot be extinguished using water , and only dry chemical class D fire extinguishers can extinguish the fires . 
