(Salem, OR)  --  The Oregon State Penitentiary in Salem is on lockdown again, following a fight among inmates.  Prison officials say the brawl involved about 20 inmates and broke out around 7:30 last night.  Staff members used a chemical spray to defuse the situation.  It's the second time in a week the state penitentiary was placed on lockdown.  The first time was Monday, after a fight involving about 60 inmates.