The final word on early warning
Coming into force on July 1st 2016 the latest SOLAS X1-1/7 - MSC.1/Circ.1477 & MSC.1/Circ.1485 regulations require all ships engaged in international voyages to have, at the very least, one portable 4-gas detection unit on board. A vital piece of equipment for crewmembers entering any enclosed space or tank, this unit should be able to measure the presence of oxygen, flammable gases or vapours, carbon monoxide and hydrogen sulphide.
However, Wilhelmsen Ships Service (WSS) believes the current use and indeed abuse of many existing detectors clearly illustrates that regulation alone can only achieve so much. What is positive is the focus towards crew training requirements, but in isolation its impact will be severely limited by a widespread lack of knowledge, poor maintenance routines and inconsistent testing.
There are some basic maintenance tips, which should be second nature to crew. But the evidence suggests that even such rudimentary tasks are sometimes neglected.
Leo Francke, Safety Service Technician (Electrical) WSS Netherlands re-calibrates and repairs gas detection units on a daily basis and sees many common, avoidable flaws. “All ships need to have multi-gas instruments to comply with regulations, but some never ever use them. They are forgotten somewhere in a drawer and when they have to use it, the battery is completely flat.”
So first things first, rechargeable batteries should be replaced according to manufacturers’ recommendations or when the runtime is less than the shortest work shift, whichever comes first. Most detectors will have a low battery alarm, but nobody wants to bet their life on it, so change batteries sooner rather than later.
Along with the unpredictability of run time in low battery mode, another totally unseen issue with detectors with drained batteries is lost type and serial number.
“On some detectors after the battery goes flat, even once new batteries are fitted the instrument forgets that it was equipped with a dual range sensor for combustible gases. All that is left is the lower range (0-100%LEL) and without applying test gas the customer will never notice,” says Francke.
In addition to battery replacement, obvious as it sounds, crew should also get into the routine of placing batteries on charge after using the detector. If a crewmate finds the instrument’s battery dead they may gamble and enter an enclosed space without it. Don’t allow this temptation, charge batteries after use.
Visual and audible alarms should be checked daily and of course the audible alarm should be loud enough to be heard in the working environment. Grime and fluff can block the buzzer, so sounding the alarm before use is a necessity.
Also, check visual alarm LEDs as these can fade over time or be damaged by dropping or banging the unit. LCD displays should also be checked before use as missing segments on a display could prove fatal.
Sensitive to the elements
Irrespective of the quality of their construction, a host of operational and environmental factors can drastically affect the accuracy of gas detectors.
Robust in design, but often delicate internally, gas detection units have unique issues which crew need to be conscious of. Andrew Sheriff, Business Manager at Wilhelmsen Ships Service, states that the firm’s range of gas detectors are all MED wheel-marked, which is a minimum requirement for units used on vessels, as these are tested for a tough environment. Also, choosing the right unit for the vessel type and usage can be a challenge. What is clear is that ships must, in accordance with the regulation, ensure they have a minimum of one 4 – gas instrument.
Gas detection monitors are either electrochemical or catalytic. Combustible sensors are typically catalytic, containing pellements that react to combustible gases. If the pellements are blocked by poisons or contaminates they prevent the gas from reaching the pellement. Catalytic sensors, for example, are particularly sensitive to silicone-based substances. So, when detectors are stored next to silicon products such as kit or oil, a layer of silicon can cover the pellistor causing the sensor to fail.
In addition, high concentrations of combustible gas can actually irreversibly damage pellements rendering detectors completely useless. Francke says, “Some crew members like to test the detectors with a cigarette lighter, unfortunately this destroys the pellistor immediately due to too high a concentration of gas. In both cases you won’t notice the sensor is defective without test gas.”
Despite their rugged construction and drop test credentials, another frequently observed problem with detectors is cracked housing. Allowing the ingress of water that corrodes circuit boards, this can leads to component failure and /or shorts. An often-unseen threat, a cracked case can cause the instrument to fail, but it can also be extremely dangerous. Francke says, “It’s not always clear for the user, but the instrument can actually cause an explosion when it is no longer gas tight.”
With such a variety of factors potentially affecting detectors, crew should already be in the habit of performing a basic ‘bump’ test before use. By no means fool proof, it is however the most effective check currently available on board. In very simple terms, untested should equal unusable.
The Bump Test: A nudge in the right direction
The International Safety Equipment Association (ISEA) defines a bump or function test as a qualitative check where the sensors are exposed to challenge gas for a time and at a concentration to activate all of the alarms to at least the lower alarm settings. It proves that gas can reach the sensors, that they can respond to the gas and that the alarm will trigger. This is quick and easy to perform by crew, but does not measure a gas detector’s accuracy, the precision of the sensors, or the remaining battery life.
In order to measure the performance of the sensors a ‘calibration check’ using a traceable source test gas, at a set concentration, must be done. Measuring the sensor’s responses according to the detector manufacturer’s acceptable limits, which can vary from brand to brand, this test is much more difficult to perform on board.
Requiring prior detailed knowledge of the manufacturer’s preferred calibration settings and means to apply the gas, while it is not totally inconceivable crew can consistently administer calibration checks, the growth of on shore service providers and sales of so-called self-calibrating base stations illustrate the difficulties with calibration.
A skilled technician who often has to rectify issues resulting from poor maintenance work, Franke is unequivocal in his view of exactly who should be entrusted with calibrating detectors.
“Although people on board are using the gas detectors regularly, most of them have actually never read the user manual. Personally, I would like to have my gas detector calibrated by a professional before going into a tank when my life depends on it.”
Wilhelmsen Ships Service supports this view and it is exactly why Unitor multi gas detector units, such as the Unitor Gas Pro, are now taken care of on board by our own technicians.
Dispensing with time-consuming exchanges of units with service centres or additional investments in calibration kit, our port sales or service engineers can re-certificate, calibrate and inspect gas detectors on board quickly and efficiently as part of a visit to test or inspect other equipment.
Fast and efficient, when it comes to equipment as important as gas detection units calibration really should be done by professionals.