The Fifth edition of International Safety Guide for Oil Tankers and Terminals (ISGOTT5) recommends the fitting of combustible gas detectors in the accommodation intakes for the HVAC system. This is to ensure that flammable gas is not sucked into the accommodation areas of a tanker and thereby risking an explosion.
The accommodation units on ships have never been considered as hazardous areas and therefore are not equipped with certified equipment. This means that there are many sources of ignition in these areas and therefore the prevention of explosive gas getting into these areas is essential. For many years it has been traditional to close the vents during loading and unloading of cargo. Unfortunately, this has the major drawback that it prevents the accommodation maintaining positive pressure essential to prevent the ingress of gas from other sources. Therefore, it is considered dangerous to operate the HVAC systems in full recycling mode with the vents closed.
Forced ventilation using gas detection in the intakes is the best way to maintain a safe atmosphere in the accommodation unit during loading and unloading procedures. This will give the positive pressure required to counteract the pressure drops due to door opening/closing and the use of extraction fans in the gallery areas.
It is also essential that only monitored inlets to the Air Conditioning units are used during this period and any window units for example are switched off.
By monitoring the HVAC inlets, an alarm can be sounded well before the lower explosive limit (LEL) is reached and executive actions such as suspending the cargo transfer until the combustible vapour has been eliminated, can be implemented.
The GMI Active-8 is ideal for this application as it can monitor up to eight combustible sensors and provide the alarm activation’s required by the vessel philosophy via volt free contacts or 4-20mA outputs if required. The Active-8 has all the necessary approvals for shipboard equipment including Marine Equipment Directive approval from Lloyds Register. All GMI sensors are certified for hazardous area use and are available as catalytic type or Infrared sensors.
GMI recommend the use of the GMI infrared flammable sensor as this is a particularly good option for shipping applications for the following reasons: The GMI infrared sensor is far more stable than traditional gas sensors and therefore the regular calibration periods can be extended. These periods are always based on operational experience, however, experience shows that often periods of one year or better are achievable giving large cost savings due to the reduction of service visits required. Additionally, infrared sensors have expected lifetimes over three times longer than traditional catalytic sensors, thus increasing system availability and reducing the total operating costs over the lifetime of the vessel.
GMI are more than happy to discuss your particular requirement for detection and will be able to propose the best system for your needs. This service is provided free of charge and without any obligation, so please call GMI +44 (0) 141 812 3211 and ask for Fixed Systems Applications Team or alternatively, email our sales team.
As an ISO 9001 approved company, GMI Ltd’s quality assurance programmes demand the continuous assessment and improvement of all GMI products. Information in this article could thus change without notification and does not constitute a product specification.
Please contact GMI or their representative if you require more details.