International Gas Detectors (IGD) was approached by a client who operates a laboratory complex complete with liquid nitrogen storage. The liquid nitrogen is transferred into various containers and utilized by staff in various processes within the company.
From the client’s perspective, the currently installed gas detection system, that was acquired from a competitor, was having issues in terms of false alarms. During normal activities, the alarms were repeatedly triggered for no apparent reason. From the client’s end, the gas detection system is primarily utilized to report exceptional circumstances of gas leak, and should thus be inactive during normal working practices. The client sought a solution for an oxygen detection system from IGD.
The Client’s Concern
The client was mainly concerned about the incorrect placement or installation of detectors for site operations. It was also suspected that alarms were overly close to “normal” operational levels for their activities.
IGD went to the laboratory complex and facilitated a gas hazard overview of the site as well as its activities. With the help of consultants at the design stage, IGD also reviewed sensor placement. Upon inspection, it was found that oxygen detectors showed a range of different readings, from 19.8% to 20.9% v/v Oxygen (atmospheric oxygen is 20.9% v/v oxygen); meanwhile, site alarms were set at 19.5% v/v for room evacuation.
The Problem with Lead-Based Oxygen Sensors
The laboratory’s oxygen detection system was found to be an older model of a lead-based sensor technology. Typically called ‘legacy’ sensor, such type of detector deteriorates after a certain time period, ultimately sacrificing its reliability and performance.
Lead-based oxygen detection systems consume their working electrode over the life of the sensor. The ability of the cell to produce sufficient signal output reduces when the surface of the working electrode reacts from lead into lead oxide. As a result, gas readings drift low towards the alarm point.
When the performance of the gas detector starts to falter, the difference between normal and alarm point functions is reduced, thereby causing unwarranted alarms even for small gas releases. As this dysfunction continues, the sensor would drift below alarm point and trigger.
The normal response for this problem is to re-calibrate the device; however, such a method is only temporary since the consumption is cumulative and the drift may re-occur faster. Along with standard operational transient nitrogen releases, the effects of sensor aging or deterioration could be seen.
Due to their inherent shift life span and consequent unreliability, lead-based cells in detection systems are not utilized by IGD. The group instead manufactures oxygen detection systems based on solid polymer technology, an advanced method that is not consumptive and is also RoHS compliant.
IGD’s sensors offer competent oxygen monitoring with a life span of more than 7 years, between 5 and 10 times longer than typical lead-based sensors. While a simple product specification may have benefitted this change, the utilization of a more advanced material for oxygen detection systems paved the way for the eradication of nuisance alarms.
Solid polymer oxygen cells have been empirically proven to maintain output levels beyond their expected five-year life span. Consequently, the initial drift issue was nullified with IGD oxygen detectors.
Oxygen detectors directly monitor atmospheric oxygen at their location. Placement is initially dependent on the displacing gases’ vapor density. In the particular problem presented in this article, nitrogen is discussed as cryogenic nitrogen at low temperature but high density. Any initial spill will occur at floor level, and any vapor will mix with the normal atmosphere, working to displace the oxygen.
To provide a solution to the client’s concern, IGD upgraded the detectors to its solid polymer-based units. Simultaneously, two sets of detectors were fitter. One set, located at floor level, spills. This is alarmed as a warning, enabling ventilation rates to increase. Meanwhile, the second set of detectors, located in the breathing zone, were made to escalate alarms into an evacuation state until such time that ventilation returns the area to normal operation.
After the installation of the new detector systems, the client has seen significant reductions in nuisance alarms. With staff following appropriate evacuation and ventilation procedures, actual releases are properly detected.
IGD’s solid polymer oxygen cell enabled the client to have extended lifetime cost savings, along with enhanced stability that significantly reduced false alarms.
This information has been sourced, reviewed and adapted from materials provided by International Gas Detectors Ltd.
For more information on this source, please visit International Gas Detectors Ltd.