Speed and safety are an unlikely pair in everyday life but in the manufacturing industry they often go hand-in-hand. Specifically, the speed of response when measuring hazardous gases and vapors.
NFPA 86 requires the use of continuous analyzers to measure the potential flammability of vapor concentrations in any oven or dryer zone exceeding 25% LFL, “It can not be emphasized too strongly that the solvent vapor concentration measurement system is to have a very fast response time so that corrective action can be taken in response to upsets such as excessive introduction of solvent into the oven…A response time of as little as 5 seconds might be required in some cases" (NFPA 86).
The speed at which a sample is drawn from the process and reaches the analyzer's detector is critical. Long sample lines, lines with small radius bends or in-line sample conditioning filters, can induce dangerous delays. To combat these issues and to ensure the highest degree of safety the following goals should be met:
- Both the analyzer and the sample lines must be warmer than the flashpoint of the vapors traveling through the sample stream - Condensation of any substance in the sample stream, even those which are not of interest, can cause sample flow restrictions or clogging.
- The analyzer should contain it's own alarm relays, connected to the controls of the user's corrective device. For example, the danger alarm relay should directly activate the process emergency stop, fan speed, damper release, or whatever action is appropriate.
Keep in mind the speed of a flammable vapor monitoring system is the sum of its parts; sample transport, detector response, alarm activation, and corrective action. To find out more details on how your response time effects the safety of your application, read this application note or blog post.