A fixed CO2 system in the machinery space is about to be activated following a confirmed engine room fire. The Chief Engineer is pressing for immediate activation. As the officer responsible for the muster, what must happen before activation, and why can this not be skipped under pressure?

A. CO2 PRE-DISCHARGE HEADCOUNT — NON-NEGOTIABLE STEP: Before any fixed CO2 (or equivalent gas) system is activated in an enclosed space, a confirmed headcount/muster must establish that no person remains in or near the space to be flooded with extinguishing gas, and the space must be evacuated and sealed (ventilation stopped, openings closed) — CO2 displaces oxygen and is lethal to anyone remaining inside, with no warning a casualty can act on once concentration builds. WHY THIS CANNOT BE SKIPPED UNDER PRESSURE: (1) A fire that is already serious enough to warrant CO2 discharge is already a controlled, contained situation in terms of timeline — the marginal extra time to confirm headcount is small compared to the risk of killing a crew member who is unaccounted for in or near the space; (2) "Pressing for immediate activation" is a recognised pattern (time pressure overriding a safety-critical check) that has caused real fatalities in machinery space fires across the industry — the officer responsible for the muster must hold the line on this check regardless of seniority or urgency being expressed by another officer; (3) The pre-discharge alarm (audible/visual warning before gas release) must also be allowed to run its full warning period, not be bypassed. ESCALATION: if there is any doubt about whether all persons are accounted for, activation must be delayed and the search/muster completed first — a fire emergency does not suspend this requirement.

B. Headcount can be skipped if the fire is confirmed and time-critical, since speed of extinguishing the fire takes priority over confirming crew location.

C. Headcount is only required for machinery spaces above 500GT; smaller coded yachts may activate fixed CO2 systems without a pre-discharge muster.

D. The pre-discharge alarm period exists only to warn nearby machinery of the discharge, not to protect personnel — it may be silenced to save time.

A. STRUCTURAL FIRE PROTECTION SCALING UNDER THE CODE: For yachts at or above 500GT, structural fire protection requirements are derived from SOLAS passenger ship rules applicable to ships carrying fewer than 36 passengers — meaning more extensive fire-resisting bulkhead/deck divisions, stricter fire integrity ratings, and more comprehensive main vertical/horizontal zone subdivision. Below 500GT, the Code applies a proportionately reduced standard reflecting the smaller scale of the vessel and lower absolute fire risk exposure, while still requiring proper compartmentation and insulation standards (e.g. A-class/B-class divisions appropriate to the space). PRACTICAL EFFECT: a 600GT yacht crossing the 500GT line must meet the more demanding passenger-ship-derived standard in full, while a 480GT yacht just under the line is not required to meet that same level — this is precisely why GT, not just length or layout similarity, drives a real difference in required fire protection between two superficially similar vessels. CREW IMPLICATION: an officer transferring between a sub-500GT and a 500GT+ yacht should not assume the same fire safety standard or zone layout applies — review the specific vessel's fire control plan and CCC rather than relying on experience from a similarly-sized yacht under a different tonnage band.

B. Tonnage has no bearing on structural fire protection standards under the Code; all coded yachts above 24m regardless of GT must meet an identical fixed standard.

C. Fire protection standards are set entirely by the yacht's classification society on a vessel-by-vessel basis with no reference to GT thresholds in the Code itself.

D. The 500GT threshold only affects manning requirements, not fire protection — fire safety standards are governed solely by passenger numbers under the Code.

A. A-CLASS / B-CLASS FIRE INSULATION STANDARDS — MACHINERY SPACES: Under the Code's structural fire protection requirements, decks and boundaries enclosing machinery spaces must be insulated to reach a defined fire-resistance standard for a defined period: A-30 means the division must remain effective as a fire/smoke barrier and limit temperature rise on the unexposed side for at least 30 minutes under standard fire test conditions, required for vessels in UNRESTRICTED SERVICE (i.e. capable of extended ocean passages, away from immediate rescue/shore-based fire support). B-15 is a lower fire-resistance class (15 minutes) permitted for vessels operating only in SHORT RANGE NAVIGATION (a more limited area, generally closer to shore/assistance), reflecting the reduced risk exposure and faster potential access to external assistance. WHY THE DIFFERENCE EXISTS: the Code's structural fire protection requirements are calibrated to the realistic time a crew may need to contain and fight a fire before either bringing it under control or reaching a point where external assistance/evacuation becomes practical — a vessel restricted to coastal/short-range operation can rely on a shorter self-sufficiency window than one on an unrestricted ocean passage far from any assistance. PRACTICAL POINT FOR CREW: the vessel's actual service notation (unrestricted vs short range) is not just an operational limitation — it is tied directly to the fire insulation standard the vessel was built and surveyed to, so operating outside the certificated service notation can mean operating with fire protection inadequate for that profile.

B. A-30 and B-15 refer to the colour-coding of fire extinguishers required in machinery spaces, not to structural insulation standards.

C. A-30 applies to short range navigation vessels and B-15 applies to unrestricted service vessels — the reverse of the higher standard being for greater self-sufficiency.

D. These classifications are obsolete terminology from LY1 and no longer appear in any current edition of the Code.