Firefighters have declared an impasse in a long-standing contract dispute with the city. The impasse triggers a process approved by voters in November to appoint a neutral party to decide contract issues. Richard Chavez, Anaheim Firefighters' Assn. president, said 98% of the union's members voted to declare an impasse. Firefighters have been working without a contract since July 1996, and the union presented its last offer to the city Feb. 19. Firefighters are seeking, among other things, a cost-of-living increase, Chavez said.