Green metal bins have popped up at the nation’s eighth-busiest airport, creating a safe space for airline passengers to dispose of marijuana. Even though recreational marijuana is legal in Nevada, the drug is banned inside Clark County’s network of airports and security checkpoints. “Marijuana is not allowable anywhere inside the buildings, be it pre- or post-security,” airport spokeswoman Christine Crews said. About 20 so-called “amnesty boxes” were installed over the past week outside high-traffic areas of McCarran, Henderson Executive and North Las Vegas airports.