The PHS is largely reserve force comprised of health professionals including doctors, nurses, pharmactists, technicians, dentists, researchers and santiation engineers. Although it is funded by the Sivadian government, its mandate includes providing support to other worlds in distress when invited by host governments. Consequently a large proportion of its personnel are not Sivadian citizens. Reserve members of the PHS may be called up in response to public health emergencies. They also participate in regular training exercises. For reservists, service in the PHS is always voluntary.