Keys to proper alarm system maintenance
November 3, 2020 By Freshwater Institute
Even the most well-maintained and managed RAS will have deviations from normal operating conditions. A robust system design that includes back-up and emergency life support equipment can mitigate risks. However, alarming features that quickly alert staff to a potential issue are critical to return a RAS to normal operating conditions as quickly as possible. Ideally, alarms will be few and far between at a well-managed farm. Because of this, alarming equipment should be regularly tested to confirm proper working order.
Dissolved oxygen (DO) is the most important water quality parameter to monitor in RAS. Low DO concentrations in the culture water can quickly lead to stressful or life-threatening conditions for the fish. In order to test a DO alarm, either move the DO probe to a container of water with low dissolved oxygen or manipulate the alarm set points programmed in the monitoring equipment to be higher than the current concentration in the tank. When manipulating set points, be sure to note the normal settings before adjusting. Once a manipulated alarm condition has been created, confirm that monitoring equipment recognizes the alarm. Next, confirm that the dial-out system is activated and confirm that staff receive the appropriate phone call or text alert. After confirming alarm detection and alerts, be sure to return the probe to the appropriate location or the alarming set points in the monitoring equipment to their normal settings.
Emergency life support systems should be integrated with dissolved oxygen monitoring to activate when potentially dangerous conditions are detected. While checking for successful alarming and dial out alerts, be sure to confirm that emergency back-up measures activate and are in good working order. Emergency oxygen diffusers should be sized to maintain a static tank at full stocking density until staff can arrive but are impractical to test in a live setting. Managers should closely observe oxygen output from diffusers to confirm performance is as close to design specifications as possible. This can be done by looking for increasing DO concentrations in the culture tank while diffusers are on and by looking at the size and amount of oxygen bubbles reaching the water surface. The amount or size of the bubble cloud should be consistent from month-to-month. Diffusers with declining oxygen output should be removed and cleaned with a scrub brush or pressure washer and retested. A cleaned diffuser that still does not provide adequate performance should be replaced. Large bubbles coming from a diffuser can indicate a hole in the gas line, poor connections, or damage to the diffuser material. Leaky oxygen lines or connections should be repaired, and damaged diffusers replaced.
Strategically placed level indicator switches are a valuable tool to detect deviations from normal flow rates in a RAS. Abnormal flow can indicate equipment failure or decreased performance that will impact system water quality. To confirm that level indicator switches are working correctly, reach into the water to depress the switch or float until an alarm is triggered. This can also be done by removing a switch from the water and allowing it to hang freely in the air. When removing any level indicator switches, be sure to clearly mark the normal operating height for return to use. Any level indicator switch should be set at such a height to accurately detect real alarms, but not so high that normal turbulence at the water surface creates chattering from constant up and down motion from the switch. Like DO, confirm that level alarms correctly activate and that dial-out functions reach emergency response staff.
In addition to alarming, level indicator switches can provide protection for both equipment and staff. For example, level indicator switches incorporated into system pump controls can automatically shut off pumps if sump levels are decreasing to the point that pumps could entrain air or operate dry and turn pumps on again when safe water levels are achieved. Likewise, level indicator switches connected to oxygen or ozone generators can automatically shut off gas flow if water levels are such that a leak into the working environment is possible, saving money from wasted gas and protecting staff from hazardous exposure. When testing level indicator switch alarms, also confirm that secondary functions are working properly.
Monitoring and alarming function should always be tested during commissioning and restart of a RAS. They must be confirmed to be in good working order before stocking fish into the RAS. Alarms should be tested monthly at minimum, but facilities just coming online or implementing new RAS should check alarms more frequently until confident in the reliability of the equipment. Knowing that alarms will work and notify staff of issues that need immediate attention can provide peace of mind and ensure the overall success of the operation.
For more information please visit www.freshwaterinstitute.org.
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