Due to the nature of the sensitive equipment inside control room cabinets, it is useful to ensure the use of "T-rated" firestops, that are massive and thick enough to resist heat transmission to the inside of the control room. It is also common to place control rooms under positive pressure ventilation to prevent smoke or toxic gases from entering. If used, gaseous fire suppressants must occupy the space that is to be protected for a minimum period of time to be sure a fire can be completely extinguished. Openings in such spaces must, therefore, be kept to a minimum to prevent the escape of the suppression gas.