Place it right after the rescue character appears on screen, following an enemy spotted cue to set up the threat first. Follow it with the bomb has been planted line only in a tactical round recap, keeping the scientist's arrival moment as the payoff.
About this sound
This clip is a three-second voice line from a scientist character who spots an arriving soldier and declares he is saved at last in a grateful tone. It feels relieved and unintentionally funny, turning frantic gratitude into a tiny rescue celebration. The line comes from Half-Life, where its scientists greet armed help with dramatic relief.