The UK Maritime and Coastguard Agency has released an amendment to MGN 657 (M+F) Amendment 1 requirements for fixed aerosol fire extinguishing systems for use in small vessel machinery spaces.
The update clarifies that the design density should be calculated based on the net volume of the protected space, as well as clarifying the test criteria including the pass/fail criteria and arrangements for the test mock-up.
Background
Approval of Fixed Aerosol Fire Extinguishing Systems for use in small vessel machinery spaces has previously been undertaken by the MCA, with the publication of this notice those approvals will now be undertaken by a UK Approved Body. Small vessels are those vessels as referred to in Section 6 of the appendix. Once a system was approved the manufacturer or supplier of the system was issued with the MCA Certificate of Inspection and Test (MSF 1814 form). The certificate demonstrated the safe and effective operation of the system following various fire-extinguishing tests. These tests included a demonstration of the system’s ability to extinguish a selection of representative fire types in an enclosure similar to that of a small vessel’s machinery space.
This MGN formalises the process by publishing the test requirements for future approvals and to require that the tests are witnessed and confirmed as successful by a UK Approved Body.
Key changes
In regard to calculating the design density, the machinery space housing the Fixed Aerosol Fire Extinguishing System is referred to in this document as the protected enclosure or protected space. The protected enclosure volume should be calculated by the system supplier or installer and agreed by the vessel owner, equipment supplier and supplied to the surveyor for acceptance, as noted in section 5.2 of the MGN. The required concentration of the aerosol varies between manufacturer / system types, and agreement of the design concentration required for the space should be sought from the manufacturer or their agent and be based on fire extinguishing tests as defined in this document. The methods used for calculating the design concentration shall be included in the vessel’s application for certification. The quantity of extinguishing agent for the protected space should be calculated at the minimum expected ambient temperature using the design density based on the net volume of the protected space, including the casing. The net volume of a protected space is that part of the gross volume of the space, which is accessible to the fire-extinguishing agent.
The recently published amendment also clarifies the test criteria including the pass/fail criteria and arrangements for the test mock-up.
Success Criteria:
- Class B fires should be extinguished within 30s of the end of discharge. At the end of the hold period there should be no re-ignition upon opening the enclosure.
- The fuel spray should be shut off 15 s after extinguishments. At the end of the hold time, the fuel spray should be restarted for 15 s prior to reopening the door and there should be no re-ignition.
- The ends of the test fuel trays should contain sufficient fuel to cover the bottom of the tray.
- The wood crib weight loss should be no more than 30% during the 2 min pre-burn test.
- A re-ignition test should be conducted after the successful extinguishments of the tell-tale fires in test 1 (Fire A) within 30 s after completion of discharge. The test should involve the attempted ignition of two of the tell-tale fire containers. One container should be at the floor level and the other at the ceiling level at the diagonally opposite corner. At 10 min after extinguishment of the fires, a remotely operated electrical ignition source should be energized for at least 10 s at each container. The test should be repeated at 2 min intervals two more times, the last at 14 min after extinguishment. Sustained burning for 30 s or longer of any of these ignition attempts constitutes a re-ignition test failure.