To be effective a sealed room will have no un-filtered air exchange with the outside - contaminated air. Thus if you successfully seal your safe room with duct tape and plastic and you don't provide a positive pressure filtered air flow into your safe room you will surely suffocate. This has happened in Isreal where they preached and practiced this procedure during the first gulf war. Properly constructed this approach will provide some reasonable protection from many bio-chem attacks but if you don't have electricity to run the ventilation system or your filters are faulty or clogged you will be just as dead from suffocation. Dead is dead. If you don't have the room that well sealed then the bio-chem agents will infiltrate just as readily as the Oxygen will.