Halloween is a time for ghosts, goblins & ghoul... but a really frightening thought would be having an unreliable monitoring system! Here are the essential requirements for a reliable solvent vapor analyzer that will meet NFPA 86 requirements (found in section 11.6.10):
- Active Sampling System (Sample Delivery System. 11.6.10.11) - It is recommended that process applications employ active sample draw systems to continuously deliver a sample to the solvent vapor monitor. The best sensor site is on or adjacent to the oven zone’s exhaust ductwork so that the sample line is kept short.
- 5 Second System Response Time (Speed of Response. 11.6.10.2) - System response time is the sum of the sample delivery time plus the sensor response time. This emphasizes the importance of short sample delivery lines and no sequential sampling. The caution note in this section warns operators of the need for fast response, stating that in many cases the system “shall be capable of detecting and responding to process upset conditions to initiate reduction of the vapor concentration before the concentration exceeds 50 percent of the LFL.”
- Calibration Accuracy (Accurate Calibration and Response 11.6.10.5) - This section requires calibration to be valid “for the application and solvents used.” If a variety of solvents is used, cross calibrations must be accurate or the sensor must be recalibrated whenever solvents are changed. Calibrations must be made using known concentrations of test gas mixtures.
- Avoiding Condensation (Avoidance of Condensation.11.6.10.11) - Section 11.6.10.11 requires that “the sensor and sample system shall be maintained at a temperature that prevents condensation.” Condensation can be avoided by heating the entire sample line and sensor assembly above the condensation temperature of the sample.
- Failsafe Malfunction Logic (Failsafe Malfunction Logic. 11.6.10.8) - According to section 11.6.10.8, alarms shall be provided to indicate any sample, flow, circuit or controller power failures.” The best analyzer design should be failsafe: it will provide malfunction alarm for any and all faults. For greatest safety, the malfunction alarms should shut down the process.
- Maintenance (Maintenance. 11.6.10.11) - The system should be designed to provide the least amount of downtime, including routine calibration and maintenance of the sampling system and sensor.
Making sure to meet these requirements can help to keep your plant safe and avoid any unnecessary tricks ;) Have a safe Halloween!
Add new comment