Explosive Decompression is a horrendous failure of a ship's structural integrity, whereby the outer hull is breached, and all of the compartment's atmosphere rushes out into the vacuum of space. In modern 24th Century starships, a hull breach is usually automatically sealed-off by a containment force-field to hold the atmosphere in. Additionally, all airtight doors, ventilation shafts, and other orifices are closed off, to protect the rest of the ship or station. If a human body is exposed to vacuum without protection, in less than a minute the internal pressure will cause the individual to explode (so forget about holding your breath!)