Like every other rule, NFPA rules on shutoff valves have exceptions. Section 5-7.1.2 requires that each safety shutoff valve shall automatically shut off the fuel to the burner system after interruption of the holding medium by any of the interlocking safety devices, combustion safeguards or operating controls. However, there are two exceptions to this standard, with multiple parts to each section. The exceptions state:
For fuel gas systems, where multiple burners or pilots operate as a burner system firing into a common heating chamber, the loss of flame signal at one or more burners shall be permitted to shut off those burners by closing a single safety shutoff valve, provided the following conditions (in both A and B) are satisfied.
A. For the individual burner safety shutoff valve:
1. It is demonstrated based on available airflow that failure of the valve to close will result in a fuel concentration not greater than 25% of the LEL.
2. The safety shutoff valve has proof of closure acceptable to the authority having jurisdiction.
3. The fuel burner is monitored to verify that there is no fuel flow following operation of the burner safety shutoff valve.
B. The safety shutoff valve upstream of the individual burner safety shutoff valves shall close for any of the following conditions:
1. Activation of any operating control of interlocking safety device other than the combustion safeguard.
2. When the individual burner valves do not have proof of closure or fuel monitoring as described in (A) and the number of failed burners are capable of exceeding 25% of the LEL if their single safety shutoff valves should fail in the open position.
3. When individual burner valves have proof of closure or fuel monitoring as described in (A) and verification that the individual burner safety shutoff valve has closed following the loss of flame signal at the burner is not present.
4. Loss of flame signal at all burners in the burner system or at a number of burners in the system that will result in unsafe operation.
Acceptable Exceptions?The exceptions related to safety shutoff valves are considered controversial, and it is widely believed that a number of the points in the exceptions cannot be achieved as described. Jim Roberts of Eclipse Combustion, Rockford, IL, believes that the exceptions listed in the NFPA ruling are difficult to accomplish because of cumbersome equipment requirements and the perception of high cost. "The exceptions call for something as finite as being able to control flows and fuel stoppages to the point of not allowing more than a 25% LEL buildup. That is very difficult," said Roberts. "When exceptions are more difficult than the original guideline, people wonder why they should bother."
Dick Bennett of Janus Technology Group, Rockford, IL, feels the same way. He believes that in a specific instance, it may be possible to achieve all the required conditions of the exceptions. However, he explains, "You are going to have to jump through hoops and you'll begin to doubt whether it's worth the effort."
Exceptions to the rule or not, certain agencies require valve manufacturers to supply a means for making tightness checks, and a few manufacturers do supply these means. In most other cases, it seems that safety shutoff valves are not tested because there is a lack on information available on how to perform a safety check. It falls to you to speak with the valve manufacturer or your insurance underwriter to find the information you need to properly perform tightness checks. Digging up the right information may save you from fire, explosions and loss of life. Leaving your valves to run untested for years and years on end only increases your risk of failure.