SIMI VALLEY, Calif. (AP) — For many people gathered to watch July Fourth fireworks at a Southern California park, it took time to realize the wild chain of explosions weren’t just part of the show.But those up close Thursday night knew immediately that something was wrong. They included Paulina Mulkern, who had to shove her 4-year-old cousin under a lawn chair as shrapnel came flying then shielded a 7-year-old cousin with her body as scorching debris flew overhead.“You feel the big old heat come right over your back,” Mulkern said Friday, still shaking a day after the chain reaction of accidental explosions at an annual fireworks show that had been put on since 1970 in Simi Valley northwest of Los Angeles.Thirty-nine people ranging in ages from 17 months to 78 years old were injured. Some had burns and shrapnel wounds, and some were trampled, authorities and hospital officials said.