In thread408-48267: Double-Block Valves and Double Block and Bleed Valve on 10Mar03, davefitz (Mechanical) posted a comment stating,"double block and bleed is required by code in section I (boiler) service if there are 2 or more boilers interconnected on a common steam line and the boilers have a manway in the steam drum. This is to avoid cooking the maintenance person that enters the steam drum on the idle boiler. A similar philosphy would be prudent for any pressure vessel that a person can enter , if the vessel is interconnected to another active system which has dangerous fluids."What code is davefitz refering to? I ask this because at our facility we are currently installing a second boiler that will be connected to our existing boiler. I'm not the engineer over this project, but I would like to ensure that no one could potentially be hurt.See also thread408-94849: Double Block Bleed Valve. If you are in the USA, Federal OSHA probably applies and its in their regulations that you'll find the energy isolation and entry requirements. Individual states and local jurisdictions may impose tighter restrictions. My state generally follows OSHA but is a bit tighter on some particular issues.