Valves active protection systems, water

Secondary containment systems are best described as passive protective systems. They do not eliminate or prevent a spill or leak, but they can significantly moderate the impact without the need for any active device. Also, containment systems can be defeated by manual or active design features. For example, a dike may have a drain valve to remove rain water, and the valve could be left open. A door in a containment building could be left open. 

An active fire protection system requires some action to occur before it functions per its design intent. This action may be taken by either a person or control system. Examples of active fire protection systems are monitors, water spray systems, foam systems, emergency isolation valves, and ESD systems. 

The project plan should encompass all aspects of a fire protection system, such as the underground fire water distribution system, fire pumps, aboveground water header, valving and standpipes, structural support, and detection and alarm systems. All work on the fire protection system must be coordinated with other work activities at the site or in the operating unit. The recommended installation practices for the different types of fire protection systems are covered in consensus standards, such as NFPA. The installation process is illustrated in Figure 9-1. 

Normally where it is necessary, fireproofing is preferred over water spray for several reasons. The fireproofing is a passive inherent safety feature, while the water spray is a vulnerable active system that requires auxiliary control to be activated. Additionally the water spray relies on supplemental support systems that may be vulnerable to failures, i.e., pumps, distribution network, valves, etc. The integrity of fireproofing system is generally considered superior to explosion incidents compared to water spray piping systems. The typical application of water sprays in place of fireproofing is for process vessel protection. 

The preaction system. In libraries, museums, or other locations where special contents may be housed, the preaction sprinkler system must be used. Any operation of the sprinkler system in the absence of fire would be devastating to the building contents. Most fire safety professionals identify two events that must take place in order to activate the system. First, the heat of a fire will melt the fusible link in the sealed sprinkler heads. Second, a detector must open the deluge valve to admit the water. In the absence of either of these two events, the sprinkler system will not function. The biggest disadvantage of this system is the cost. However, when contents of great value must be protected, the expense of a preaction system may not be restrictive. 

If trained to do so and confident that you are capable, activate any fire monitors and/or fixed fire water systems in the immediate area and attempt to cool the tank and surrounding equipment. If the tank is receiving material or product, close a valve on the inlet line at a safe location. Stand by to direct the Emergency Response Team (ERT) to scene Use appropriate Personal Protective Equipment (PPE) First Responder... 

Activation of layers of protection such as relief valves, interlocks, rupture disks, blowdown systems, halon systems, vapor release alarms, and fixed water spray systems... 

Retraction systems automatically withdraw the furnace camera several feet back from the firebox if the systems sense loss of either water, air coolant, or high lens tube temperature. This gives the lens additional protection from the heated air that would blow against the lens if fans stopped and negative pressure changed to positive pressure. The retraction system is often air-operated, using an air-reserve tank as a purely pneumatic system component. This makes it totally independent of electricity. On loss of air pressure, water coolant, or high lens tube temperature, a solenoid valve opens and activates a rodless cylinder to withdraw the lens from harms way. The system will not return the camera to its inserted position until the problem is corrected. 

A technical superintendent at TMI-2 who arrived on the plant at 03 45, subsequently said I had the perception that we were in a very unusual situation, since I had never seen the pressurizer level increase and stay at a high value and, at the same time, the pressure staying low. They [the pressure and the level] had always behaved in the same way . As a consequence of the described evaluation errors the primary circuit continued to lose water for hours and in addition the automatic core cooling system, correctly activated, could not perform its function of fuel integrity protection. It is now known that if the block valve had been closed after one and half or two hours or if the operation of the HPI only had not been arrested, even without the closure of the valve, the Three Mile Island accident would have been no more than a modest nuisance of operation. For completeness of information it has to be added that the possibility of an accident of the type of TMI-2 had been foreseen by some experts. If these foresights had been confirmed by in-depth theoretical studies and possibly by experimental tests, their results, duly made known to interested people, would have enabled the TMI-2 operators to correctly diagnose the fault and react correctly. 

---