Arguably regulation and the threat of punitive damages seems to be the biggest impulse to purchase fixed gas detection, on the contrary there is another angle which provides better financial decision making - situational awareness!
Most people when they hear “Ammonia leak” they conjure up this horrible incident with gruesome burns and people coughing, vomiting and dying all over the show. Of course, we must not disrespect that although something like this is rare in occurrence, it must be mitigated accordingly, in reality, it is the more frequent, low concentration leaks which ironically go "undetected” on the cheque book.
No doubt about it, Ammonia is an abundant, cost effective and high performing refrigerant, but losing your Ammonia in small amounts over time will end up costing you big time in the long run.
“Just because it is natural doesn’t mean it is free”
System optimisation – High performance and energy reduction.
Running short of Ammonia in a nut shell, means it will increase your energy bill. Furthermore, your plant will not hold temperatures as well. When your biggest cost centre is your refrigeration energy bill, you can appreciate the impact of even a 1% decrease in performance.
Less risk – In an emergency every second counts
Regardless of Ammonia’s ability to self-warn, it is improbable to imagine that you have a worker stationed at every flange, valve and fitting. Having fix gas detection in areas where product is stored will also reduce the peril of losing your valuable merchandise to Ammonia contamination. This may also look favourably in the eyes of your insurer.
Labour & equipment costs
Receiving a service call to a large Ammonia plant that is not performing requires a significant amount of investigation. It is not always as simple as looking at a computer screen or a level sight glass. Adding Ammonia to a system must not be performed in haste, a methodical approach must be taken to ensure the correct amount is charged, taking account for the dynamics of the plant operation. The equipment and safety demands of such a task will easily outweigh the cost of the Ammonia itself.
When looking at your 2019 refrigeration budget it is imperative not to overlook investing in a good quality and well-designed fixed gas detection network.
There are many detection options available, so it is easy to get confused. Aside from the initial cost, ultimately it is important to focus at the following attributes in a sensor;
- Life expectancy
- Cross sensitivity
- On-going costs
Not ideal for engine rooms as they are likely to get over saturated during maintenance.
- High accuracy (Narrow sensitivity spectrum)
- Best for low levels of detection (Occupied spaces)
- Susceptible to over-saturation
- Short life expectancy
- Frequent calibrations required
Not ideal where the possibility of exposure to mixed gases such as exhaust fumes or other chemicals.
- Susceptible to interference (Broad sensitivity spectrum)
- Long life expectancy
- Calibrations required
Suitable for high concentrations (engine room high level detection)
- Good life expectancy
- Suitable for monitoring lower flammable levels (LFL/LEL)
- Calibrations required
Open path Laser
Suitable for most areas of monitoring
- Ultra high accuracy – targeted gas wave length
- Rapid response
- No calibrations required, only bump testing
- High fidelity
- High area of coverage
- Long life expectancy
The appropriate Installation of a detector is as important as its selection, it is very common to see an engine room with a gas detector mounted on a wall that is not downstream of any Ammonia pressure equipment. (in the air flow of continuous ventilation) This is a high concern as it will not measure the space concentration effectively and as rapidly as a sensor that is mounted at a point that is anticipated to leak such as a compressor or valve grouping.
Until only recently, fixed gas detection was isolated to only the engine room, however proactive end users understand the benefits of the augmented capabilities of perimeter and point detection of outdoor areas, inside cold storage and occupied spaces. It is suggested, that one sensor is installed for every 35-50m2 of plant area to be measured. Since Ammonia is lighter than air, any high concentration (Ignition prevention) sensors are to be installed in elevated positions, however low toxicity sensors that are intended to monitor workplace exposure as well as early warning of leakage, be fitted at average human height (5’6” or 170cm)
In cold-storage areas the sensor should be mounted on the air return to avoid any issues with humidity and temperature variation when cooling or defrosting.
Monitoring the pressure relief vent should not be disregarded as second-fiddle, historically relief valves leak often and unnoticed. Receiving an early warning from an actual pressure relief activation is invaluable for the facilities ability to react and respond accordingly.
When setting parameters, there is guidance within the joint Australian/New Zealand standards 5149:2016 however where integrating the detector to a programmable logic controller or SCADA your choices and functionality is immense. I advise end users to adopt a combination of the workplace exposure standards and AS/NZS 5149:2016, setting any additional control above or below these limits is circumstantial and should be risk based.
A stand-alone sensor without incorporation into an architecture of well thought out logic and rationale, is as a good wooden frying-pan. Fixed gas detection must provide simplistic site wide and external alert and notification and it must provide programmable actions for controlled shut down and instantaneous emergency shutdown of the plant in the event of possible flammable incident.
I encourage you to probe your refrigeration energy and maintenance costs last year; look at how much Ammonia was charged into the system, what did the total cost look like? How many Ammonia leaks were notified to management? Does your fixed gas detection cover all bases? Could greater situational awareness from a fixed gas detection network benefit your operations bottom line?
My straight up advice - don’t skimp on sensors.
By Padraic Durham