There is a saying among gas detection experts about pressurized cooling equipment: If it runs, it leaks. It's just a matter of when.
However, it pays to arrest gas leaks quickly to mitigate their consequences - today more than ever because of the economic penalties. EPA fines have increased to up to $25,000 per day per violation for anyone who vents ozone-depleting refrigerant gases into the atmosphere, including chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs) and blends. Refrigerant leaks that go undetected can waste huge amounts of energy, forcing compressors, valves and other machine components to run harder to maintain proper pressures. Over time, this extra workload can shorten equipment life significantly, adding to capital and labor expenses. Leaks also can spoil food in refrigerated compartments or contaminate other manufactured goods, forcing manufacturers to scrap product or, even worse, fight legal battles.
While worker safety often is viewed as the principal benefit of installing gas detectors, gas detectors can boost bottom-line performance through energy management, operational efficiency, worker health and property protection. But to gain the full advantage, plants must think beyond the simple standard of safety compliance and incorporate gas monitoring into an overall productivity plan.
Gas Monitoring Guidance"How many detectors do I need?" and "Where should I locate them?" are two of the most common questions about installing gas detectors - and probably two of the most difficult to answer. Unlike other types of safety-related detectors such as smoke detectors, the location and quantity of detectors required in different applications is not clearly defined.
Gas detectors should be mounted where the gas is most likely to be present. Locations requiring the most protection in an industrial plant would be around compressors, pressurized storage tanks, cylinders or pipelines. Areas where leaks are most likely to occur include solenoid and relief valves, gauges, flanges, T-joints, filling or draining connections, and welded and quick-connect fittings and devices.
Also pay attention to rooms adjacent to the room being monitored. What industrial processes are performed or what equipment is used in these adjacent areas? The gases generated in those spaces can drift into other areas and cause a toxic or combustible gas mix. For example, a mechanical room that uses flammable gases or a battery room that uses forklifts may give off carbon monoxide that potentially can mix with off-gassing elements from hydrogen-charging stations, propellants used in heating elements, and more.
Another example is ammonia leaks, which are seldom purely ammonia. Often, they are mixed with other liquids such as lubricants or cleaning solvents. These substances effectively can change the lower explosive threshold from, say, 40,000 parts per million (ppm) to 37,000 ppm.
Before purchasing gas monitoring equipment, you should conduct a gas leak audit of the process cooling environment with gas detection experts on hand to help you choose the right gas sensing technology, the right gas instrumentation installation scheme and the right mix of fixed and portable monitors. The placement of the gas detectors should be determined through collaboration. This meeting of the minds should include the advice of experts with specialized knowledge of gas dispersion; experts with knowledge of the process plant system and equipment involved; and safety and engineering personnel. The agreement reached on the location of detectors should be recorded in writing.
Designing a SystemWhen designing a gas monitoring system, keep the following considerations in mind:
- To detect gases that are lighter than air (e.g., ammonia and methane), detectors should be mounted at a high level and preferably use a collecting cone.
- To detect heavier-than-air gases (e.g., butane and sulfur dioxide), detectors should be mounted at a low level.
- Natural or forced air currents can affect how an escaping gas behaves. Mount the detectors in ventilation ducts if appropriate.
- Process conditions also can affect gas movement. Butane and ammonia, for instance, normally are heavier than air, but the gas may rise rather than fall if it is released from a process line that is at an elevated temperature or under pressure.
- Detectors should be positioned a little way back from high-pressure parts to allow gas clouds to form. Otherwise, any leak of gas is likely to pass by in a high-speed jet and not be detected.
- Detectors should be accessible for functional testing and servicing.
- When installed, detectors should point downward to ensure that dust or water will not collect on the front of the sensor.
Servicing a SystemPeriodic servicing, maintenance and calibration are vital to ensuring that fixed and portable gas detection equipment operates correctly. Gas detection applications vary widely, as do the factors that affect the frequency of servicing required for proper operation. A suitable service period that takes account of each application's unique set of factors must be established.
Traditionally, gas detection users had their own in-house service departments that were responsible for servicing, maintaining and calibrating their gas detection equipment and other safety-related equipment. Increasingly, many users now choose to outsource part or all of this function to reduce fixed costs and ensure that the equipment is maintained by people with specialist knowledge. It also is becoming more common for gas detection companies to service third-party gas detection equipment as well as their own. As users continue to demand better efficiencies from outsourced suppliers, the trend likely is to require gas detection companies to offer a "one-stop shop" for the service and maintenance of complete safety systems. Gas detection company service departments also offer site surveys, installation, commissioning and training.
Properly commissioning a system involves ensuring that it is fully functioning as designed and accurately detecting gas hazards. Many companies require that employees who use personal gas detection equipment or work in areas that have fixed systems installed are formally trained on the use and routine maintenance of the equipment. Service training departments might offer certified training courses designed to suit all levels of ability.
The modular design of modern gas detectors enables more efficient servicing. The replacement of modules rather than component level service/repair reduces turnaround time and therefore system downtime.
In addition, some gas detectors now include "smart" sensors that are precalibrated, so they can be fitted and used without additional field calibration and setup. The use of intrinsically safe designs also can allow a "hot swap" of these sensors without removing power from the detector. Other developments include automatic calibration ("auto-cal") routines that lead the user through a sequence of on-screen calibration steps to ensure correct setup. Such changes help keep service times to a minimum while ensuring accurate calibration.
In conclusion, early detection of gas leaks is a mission-critical task. Adopting a gas monitoring program from the standpoint of operational efficiency as well as compliance can pay dividends by increasing the return on investment from the gas detectors and boosting overall bottom-line performance.