The cargo pump room is the one place on a modern oil tanker where the protection wrapped around the cargo tanks runs out. A double-hull tanker built to Regulation 19 carries its oil inside a protective envelope of wing tanks and a double bottom. The pump room, set transversely across the after end of the cargo block and reaching down to the keel, historically sat on a single bottom plate. One grounding contact under that space could open the pump-room bottom, flood the room, disable the cargo and ballast pumps, and put the crew’s first line of pollution response out of action at the worst moment. Regulation 22 of the revised MARPOL Annex I addresses that single gap. It requires a double bottom under the pump room so that a grounding contact has to breach two skins, not one, before it reaches the machinery that controls the cargo.
The rule reads short, three clauses and a formula, but it carries the same naval-architecture reasoning that produced the double hull a decade earlier. The number it turns on, the protective distance , is the vertical clearance the regulation buys between the keel and the floor the pumps stand on. This article works through the scope, the formula, the exemption, the casualty history that produced the rule, and how a surveyor confirms the protection is there.
Where Regulation 22 sits in Annex I
MARPOL Annex I was revised in full by resolution MEPC.117(52), adopted by the Marine Environment Protection Committee on 15 October 2004 and entered into force on 1 January 2007. That revision renumbered and reorganized the whole Annex into seven chapters. Regulation 22 lives in Chapter 4, “Requirements for the cargo area of oil tankers,” Part A, “Construction,” alongside the structural rules that govern tanker hull form. Its title in the consolidated text is “Pump-room bottom protection.”
Two regulations in that same 2004 revision were entirely new, Regulation 22 and Regulation 23. Both responded to the same observation: the double-hull rule, adopted after Exxon Valdez, protected the cargo tanks but left other oil-bearing or oil-handling spaces exposed. Regulation 22 protects the pump room. Regulation 23, “Accidental oil outflow performance,” sets a probabilistic ceiling on how much oil a tanker may spill in collision and grounding scenarios and applies to oil tankers delivered on or after 1 January 2010. The pump room reading of Regulation 23 and the structural reading of Regulation 22 are two faces of the same goal, keeping oil inside the ship when the bottom is torn.
The chapter that holds Regulation 22 also holds the older protective rules that built up to it. Regulation 18 introduced segregated ballast tanks and their protective location, the first idea that ballast space could be placed where it shields cargo. Regulation 19 made the double hull mandatory for new tankers. Regulation 22 took the next logical step and asked why the pump room, the one space still over a single bottom, should be left out. The damage-stability rules of Regulation 28 then assume the protected hull form Regulations 19 and 22 deliver. Read together, Chapter 4 is a single argument about keeping the hull intact, and Regulation 22 is the clause that finishes it at the after end of the cargo block.
Scope: who has to comply
Regulation 22 applies to oil tankers of 5,000 tonnes deadweight and above, constructed on or after 1 January 2007. Both conditions have to be met. A 4,000 DWT product tanker is below the deadweight threshold and the rule doesn’t reach it. A 60,000 DWT crude carrier whose keel was laid in December 2006 is above the threshold but predates the construction date, so it too sits outside the mandatory requirement.
“Constructed on or after 1 January 2007” follows the standard Annex I definition of the construction date. A ship is “constructed” on the date its keel is laid, or when it is at a similar stage of construction, which the convention pins to the earlier of two markers: construction identifiable with a specific ship has begun, or assembly of that ship has commenced comprising at least 50 tonnes or one per cent of the estimated mass of all structural material, whichever is less. The practical effect is that a tanker ordered well before 2007 but with steel cutting starting after the date can still fall inside the rule. Owners and yards read the construction date carefully for orders that straddle the boundary, because it decides whether a double bottom under the pump room is a contractual obligation or an option.
The deadweight cut at 5,000 tonnes is the same threshold MARPOL uses across several of its tanker construction rules, and it isn’t arbitrary. Below 5,000 DWT, tankers are small enough that their bottom structure, draft, and trading patterns present a different risk profile, and the cost of a mandated double bottom under the pump room would weigh heavily against a modest pollution exposure. Above it, the deadweight, the draft, and the volume of cargo at stake justify the structural insurance. The number lines up with the wider Annex I drafting logic, which repeatedly treats 5,000 DWT as the point where full structural protection becomes proportionate.
Smaller tankers and pre-2007 ships aren’t left entirely unprotected, because the casualty record that produced Regulation 22 also fed national and regional practice. Some flag administrations recommend pump-room bottom protection on a voluntary basis for ships outside the mandatory scope, and a few newbuilding specifications adopt it as a class notation regardless of size. But the binding obligation is the one in Regulation 22, and it is precise about its limits.
The protective distance: h = B/15
The core requirement is dimensional. The pump room must be provided with a double bottom such that at any cross-section the depth of each double bottom tank or space is enough to give a protective distance between the bottom of the pump room and the ship’s base line, measured at right angles to the base line, of not less than:
with an absolute floor:
Here is the moulded breadth of the ship in meters, defined as the greatest breadth amidships measured to the moulded line of the frame for a metal ship. The base line is the horizontal reference plane through the top of the keel at the midship section, the same datum the rest of the convention uses for vertical measurements. Measuring “at right angles to the ship’s base line” means the protective distance is the vertical clearance, not a distance along a sloped or stepped bottom, so a rising bottom toward the bilge doesn’t earn credit it can’t deliver in a flat grounding.
The formula puts a band around the answer. Take the breadth, divide by fifteen, then bound the result. If comes out above 2 m, the 2 m cap holds, so the rule never demands more than a 2 m double bottom no matter how wide the ship. If falls below 1 m, the 1 m floor holds, so even a narrow tanker gets a meter of clearance. For most tankers in scope the answer lands between those bounds. A breadth of 32 m gives m, which the cap pulls back to 2.0 m. A breadth of 20 m gives m, which sits inside the band and stands as the requirement. A breadth of 12 m gives m, which the floor lifts to 1.0 m.
Worked numbers across the fleet
A 50,000 DWT Aframate product tanker with a moulded breadth of about 32 m needs of 2.0 m, because m and the 2 m cap applies. A Suezmax of 48 m breadth gives m, again capped at 2.0 m. A handy-size tanker of 27 m breadth gives m, inside the band, so the requirement is 1.8 m. A small coastal tanker right at the 5,000 DWT threshold with a breadth near 16 m gives m, just above the floor, so 1.07 m governs. The pattern is plain: the wide ships are all held at the 2 m ceiling, and the band only bites on the narrower hulls between roughly 15 m and 30 m of breadth. The cap means a VLCC and a mid-size tanker carry the same 2 m of pump-room bottom protection, which keeps the rule proportionate at the top end rather than forcing ever-deeper double bottoms on the largest hulls.
The “at any cross-section” wording matters at survey. The pump room isn’t a simple box; its bottom can step and its tank top can follow the rise of floor toward the after end. The protective distance has to be met everywhere across the room, not just at the deepest point or as an average. A double bottom that gives 2 m amidships of the room but pinches to 0.8 m at a forward bulkhead step doesn’t comply, because there is a cross-section where falls below the floor. Plan approval checks the worst cross-section, not the best.
Why fifteen, and why two meters
The divisor of fifteen isn’t a random constant. It echoes the breadth-scaled clearances the convention uses elsewhere in its protective-construction rules, where required spacings between an outer and an inner skin are tied to the ship’s breadth so that wider, deeper-loaded ships get more protection. A protective distance proportional to keeps the rule self-scaling: a wider hull, which generally means a deeper, heavier ship with more energy in a grounding, earns a deeper double bottom up to the cap. The 2 m ceiling then reflects a judgment that beyond a certain depth the marginal protection from a still-deeper double bottom doesn’t justify the lost cargo deadweight and the deeper, more awkward pump room. The 1 m floor reflects the opposite judgment, that below a meter the double bottom is too shallow to be a meaningful second skin, so even the narrowest ships in scope get at least that. The band between 1 m and 2 m is the convention saying the answer is always somewhere in that range, and the formula just places it.
It’s worth being precise about the variable. in the formula is the moulded breadth of the ship, the same the convention defines for use across Annex I, not the local width of the pump room or the spacing of the double bottom girders. So a ship with a narrow pump room and a wide hull still sizes its pump-room double bottom against the full hull breadth. That keeps the requirement consistent with the rest of the protective-construction stack, which all reference the ship’s , & it stops a designer shrinking the requirement by narrowing the room.
Why a single bottom under the pump room was the weak point
The pump room sits at the after end of the cargo block, immediately forward of the engine-room bulkhead on most tanker layouts, and runs from the main deck down to the inner bottom or, on a single-bottom ship, to the shell plating itself. It houses the cargo oil pumps, the stripping pumps, the ballast pumps, and the maze of suction and discharge piping that moves cargo and ballast. It is the deepest part of the cargo area that a person enters, and on pre-2007 ships it was frequently the only part of the cargo block still standing on a single skin of steel.
That geometry made the pump room the residual grounding risk after double hulls became standard. The double hull protects the cargo tanks: a grounding contact under a wing or center cargo tank meets the outer bottom, then a void or ballast space, then the inner bottom, and the oil stays put. Under the pump room of a single-bottom tanker, a grounding contact met one plate. Penetrate it, and the room floods. The cargo pumps and ballast pumps sit low in that room, often on the tank top or on plinths just above it, so even a partial flood can submerge the pumps, short their motors if electric, or break the suction that lets them work.
The consequence isn’t only the pollution from the pump room itself, which holds drainings and piping inventory rather than a cargo tank’s worth of oil. The deeper problem is operational. After a grounding, the crew’s response often depends on those very pumps: transferring cargo away from a breached tank, deballasting to lighten the ship and lift it off the ground, or running internal transfers to control list and trim. Lose the pump room early and you lose the tools to manage the casualty. Regulation 22 was written to keep that capability alive through a bottom contact, which is why its exemption is framed around the pumping system staying operable rather than around the structural breach alone.
There’s a second reason the pump room earned its own rule. It is the lowest manned space in the cargo area, and it carries a known hydrocarbon-gas and entry-safety hazard of its own. A breach that floods it doesn’t just drown pumps; it can drive oil and oily water up through the room and out through any compromised boundary, & it complicates any rescue of crew working in the space at the time. The double bottom keeps the keel contact away from that occupied volume, which is a safety benefit on top of the pollution-control one. The drafters didn’t separate the two; a dry, protected pump room serves both the environment and the people who work in it.
The pump room’s vulnerability was specific to where it sits in the longitudinal layout. On a conventional tanker the room straddles the boundary between the cargo block and the machinery space, set low so the pumps have a flooded suction head from the cargo tanks above and forward of them. That low position is exactly what the cargo pumps need to prime and exactly what exposes them to a bottom contact. Raising the whole room to escape grounding would cost the suction head the pumps depend on, so the answer was never to move the room up but to put a protected double bottom beneath it. Regulation 22 keeps the room where the pumping function wants it & shields it where the grounding risk is.
The exemption: pumping function over structure
Regulation 22 doesn’t make the double bottom unconditional. It exempts the arrangement where the bottom of the pump room is constructed so that flooding of the pump room would not render the ballast or cargo oil pumping system inoperative. The test is functional, not structural. If a yard can show that a grounding which opens the pump-room bottom and floods the space still leaves the ballast and cargo oil pumps able to do their job, the double bottom isn’t required.
In practice that points to designs where the pumps don’t depend on a dry pump-room bottom. Deepwell pumps mounted inside the cargo tanks, hydraulic submerged pumps, or pump arrangements where the prime movers and controls sit above the flooded waterline can keep working with the room flooded. A ship built around tank-mounted deepwell cargo pumps has no cargo pumps in the pump room to drown, so a flooded pump room doesn’t stop cargo transfer. The exemption recognizes that the regulation’s real aim is the surviving pumping function, and a design that delivers that function by another route has met the aim.
The exemption is not a soft waiver. It puts the burden on the designer to demonstrate, to the satisfaction of the administration, that the pumping system survives the defined flooding. That demonstration is reviewed at plan approval and recorded, and the arrangement is then bound to the way the ship is built. An owner can’t claim the exemption on a conventional pump room full of horizontal cargo pumps sitting on the tank top, because flooding that room plainly disables them. The exemption fits a specific design philosophy, and a ship that wants it has to commit to that philosophy from the keel up.
This functional framing is also what ties Regulation 22 back to the casualty rationale. The rule never cared about a dry pump room for its own sake. It cared about the crew keeping control of the cargo and the ballast after a grounding. The double bottom is the default way to deliver that, by keeping the room dry. The exemption is the alternative way, by making the room’s flooding irrelevant to the pumps. Both satisfy the regulation because both preserve the pumping function the casualty record showed was at risk.
The casualty rationale and the IMO work
Regulation 22 belongs to the post-Exxon Valdez generation of Annex I rules, but its specific target is the pump room rather than the cargo tanks. After the double-hull requirement of Regulation 19 became mandatory, attention turned to the spaces the double hull didn’t cover. The pump room was the obvious candidate, the deepest single-skin space left in the cargo block on a double-hull ship that still allowed a single bottom there. Grounding studies underpinning the accidental-oil-outflow work showed that bottom penetrations forward of the engine room could reach the pump room, and that the pump room’s low-mounted pumps were vulnerable to even modest flooding.
The Marine Environment Protection Committee took up the two new protective regulations as part of the full revision of Annex I. The Committee adopted resolution MEPC.117(52) on 15 October 2004, which contained the revised Annex I including the new Regulations 22 and 23, and the revised Annex entered into force on 1 January 2007. Regulation 22 set its applicability to that same 1 January 2007 construction date, so the rule and its trigger date arrived together. Regulation 23, the accidental-oil-outflow companion, took a later 1 January 2010 delivery date because it asked yards to run a more involved probabilistic outflow calculation across the whole cargo block, and the extra lead time let designers build the method into their newbuilding programs.
The drafting choice to make the requirement dimensional rather than performance-based for the pump room itself is worth noticing. Regulation 23 is a performance standard: compute the mean outflow parameter and meet a ceiling. Regulation 22 is a prescriptive standard: build a double bottom of at least deep, or prove the pumping function survives flooding. The Committee chose the simpler prescriptive route for the pump room because the protective mechanism is direct and the geometry is local, while it kept the harder performance route for the whole-ship outflow problem that Regulation 23 governs. The two new rules together cover the structural and the probabilistic sides of the same bottom-penetration risk.
Regulation 22 also sits next to a parallel protective rule the Committee adopted soon after, the oil fuel tank protection requirement for the bunker tanks of ships of 600 cubic meters and above of oil fuel capacity, which uses its own breadth-and-depth-scaled formulas to keep bunker tanks back from the shell. The two rules share a method, breadth-scaled protective distances with bounds, applied to two different oil-bearing spaces, the cargo pump room and the fuel tanks. They were drafted in the same period and answer the same lesson from the casualty record: a single skin between oil and the sea is the failure mode, so put a protected distance there. A surveyor working through a modern tanker’s construction record meets both, the pump-room double bottom under Regulation 22 and the bunker-tank protection on the fuel spaces, and reads them as two applications of one idea.
A subtle point of the timing is that Regulation 22 set the construction trigger at 1 January 2007 while Regulation 23 used a delivery trigger at 1 January 2010. The convention distinguishes “constructed” from “delivered” deliberately. A construction date keys off the keel-laying or equivalent stage, early in the build, while a delivery date keys off handover to the owner, at the end. The three-year gap between the two triggers, plus the construction-versus-delivery difference, meant a tanker ordered in the mid-2000s could fall under Regulation 22 but not yet under Regulation 23, then later sister ships caught both. Owners running newbuilding programs across those years tracked the two dates separately, because the structural feature each demanded, the pump-room double bottom and the outflow-optimized tank arrangement, had to be designed in at different points and proved by different methods.
The wider MARPOL family carries the same lineage. The parent MARPOL Convention and its Annex I oil regime have layered protective construction rules across three decades, from segregated ballast through crude oil washing through the double hull, each responding to a documented failure mode. Regulation 22 is one of the more targeted entries in that sequence, a single clause aimed at a single space, and it reads that way: short, specific, and bounded by a formula rather than a philosophy.
Measuring and verifying the protection at survey
The protective distance is set at design and locked in at construction, so the survey work splits into a plan-approval phase and a verification phase. At plan approval, the recognized organization acting for the flag administration checks the pump-room general arrangement and the midship and after-body structural drawings. It confirms the moulded breadth , computes , applies the cap and floor, and reads off the required protective distance. It then checks the worst cross-section of the pump-room bottom against that figure, because the “at any cross-section” wording forbids any local pinch below the requirement. The double bottom tank or void under the pump room appears on the capacity plan and the tank arrangement, and its depth is the dimension that has to clear everywhere under the room.
The space below the pump room is normally a ballast tank or a void. Where it is a ballast tank, it forms part of the ship’s segregated or other ballast capacity and is plated, coated, and fitted for ballast service, with the protective coatings that Annex-related construction standards expect for ballast spaces. Where it is a void, it is a dry protective space, gas-freed and accessible for survey, with no service function beyond the protection it provides. Either way the space has to be enterable for internal examination, because the surveyor confirms the double bottom is intact and the protective depth is real, not just drawn.
The choice between a ballast tank and a dry void below the pump room has practical weight. A ballast tank earns its keep twice: it provides the protective distance and it holds ballast, so the volume isn’t dead. But a ballast tank is wetted in service, which means it corrodes faster and carries the coating-maintenance burden of any ballast space, and a wasted inner bottom in a ballast tank under the pump room directly threatens the protection the regulation requires. A dry void corrodes more slowly and is easier to keep sound, but it is pure structural overhead, carrying nothing. Designers weigh the ballast credit against the through-life coating cost, & the survey regime then watches whichever they chose. The protective distance is the same either way; what changes is how hard the space is to keep in the condition that protects it.
The structure that delivers is the inner bottom of the pump-room double bottom, the plating the pumps actually stand on, supported by the floors and girders of the double bottom below it. That inner bottom is the second skin the regulation buys. Its scantlings come from the class society’s structural rules for a tank or void boundary in that location, not from Regulation 22 itself, which fixes only the clearance , not the plate thickness. So compliance is a two-part check: the geometry gives the protective distance, and the class rules give a sound second skin to occupy it. A double bottom of the right depth but with an under-scantled or wasted inner bottom doesn’t deliver the protection the rule intends, which is why the survey looks at both the dimension and the steel.
At the verification stage and through the ship’s service life, the protection is confirmed at the Annex I surveys that underpin the International Oil Pollution Prevention certificate. The IOPP certificate and its Form B supplement record the tanker’s construction features, and the pump-room bottom protection is part of the construction record the renewal survey confirms. A surveyor at a renewal or intermediate survey examines the double bottom space under the pump room as part of the internal examination of ballast and void spaces, checks the structure for wastage that could undermine the inner bottom, and confirms the arrangement still matches the approved plans. The protective distance itself doesn’t change with age, but the steel that delivers it can corrode, so the survey watches the condition of the inner bottom and the boundary structure of the space.
Port state control officers don’t normally measure during a routine inspection, because the dimension is a design feature recorded in the certificate rather than an operational item. What a port state control officer does is cross-check the IOPP certificate and supplement, confirm the ship’s recorded construction features match its scope, and look for clear grounds that the construction doesn’t match the documents. On an expanded inspection of an oil tanker, the officer may enter the pump room and the spaces around it and look at the general condition of the structure. A pump room standing over a flooded or wasted double bottom, or signs that a void protective space has been compromised, are the kind of findings that turn a routine check into a detailed one. The deeper verification of the protective distance stays with the flag administration and its recognized organization, where the plans and the survey history live.
The IOPP Form B supplement is the document that carries the record. It lists the tanker’s construction characteristics, and for a ship within Regulation 22’s scope the pump-room bottom protection is part of that construction history a surveyor confirms at the periodic, intermediate, and renewal surveys that keep the certificate valid. A renewal survey runs on a five-year cycle, & it includes the internal examination of ballast spaces and voids on a schedule that tightens as the ship ages. The space under the pump room comes up in that examination, so over a tanker’s life the protective double bottom is opened up, gas-freed, entered, and looked at repeatedly. The protective distance never moves, but the steel that holds it gets the same ageing scrutiny as any other ballast or void boundary, & a wasted inner bottom there is a finding that has to be repaired to keep the protection real.
Class condition-assessment and enhanced-survey programs for oil tankers fold the pump-room double bottom into the broader hull-condition picture. The enhanced survey program for tankers sets out the close-up examinations and thickness measurements the structure gets through life, and the double bottom under the pump room, being a ballast or void boundary near the after end of the cargo block, is part of the structure those programs watch. A surveyor reading wastage trends across a tanker’s bottom structure includes the pump-room double bottom in that read, because a localized loss there has the same significance the regulation cared about at newbuilding: it thins the second skin between a grounding and the pumps. The rule sets the geometry once; the survey regime keeps the geometry meaningful for thirty years.
How Regulation 22 fits the protective-construction stack
Regulation 22 reads cleanly only when you see it as the last brick in a wall the convention built over thirty years. Segregated ballast under Regulation 18 put protective ballast space where it could shield cargo. The double hull under Regulation 19 wrapped the cargo tanks in a two-skin envelope. Regulation 22 then asked the question those two rules left open: the cargo tanks are protected, the ballast is positioned to protect, but the pump room still stands on one plate, so why not extend the same two-skin logic to it. The answer was the double bottom under the pump room, sized by the same kind of breadth-scaled formula the double-hull rule uses for its own clearances.
The accidental-oil-outflow rule, Regulation 23, then sits on top of the whole protected hull. It treats the ship as a system and asks how much oil escapes across a statistical population of collisions and groundings. A ship that meets Regulations 19 and 22 already has the protected geometry that helps it pass Regulation 23, because the double bottoms and double sides that protect the cargo and the pump room are the same structure that limits outflow. The damage-stability rule, Regulation 28, closes the loop by requiring the ship to survive the assumed damage and stay afloat upright, which the protective double bottoms also help deliver by limiting the extent of flooding. The four regulations aren’t independent boxes to tick; they are one coherent design intent expressed in four clauses, and Regulation 22 is the clause that finishes the job under the pump room.
For the practitioner this stack is the difference between reading a rule and understanding it. Regulation 22’s formula looks trivial in isolation, divide the breadth by fifteen and clamp it between 1 m and 2 m. Read against Regulations 18, 19, 23, and 28, it is the deliberate extension of a protective-construction philosophy to the one space that philosophy had skipped. The number is small, the reasoning behind it isn’t.
Practical compliance and common pitfalls
The first pitfall is the construction-date boundary. An order placed in 2006 with steel cutting slipping into 2007 can pull a ship into scope that the owner thought was outside it, and the reverse can happen with an aggressive early keel-laying. Yards and owners read the construction date against the convention’s “similar stage of construction” definition, the 50 tonnes or one per cent test, because that marker, not the contract date or the delivery date, decides whether Regulation 22 binds.
The second pitfall is treating the formula as a single number rather than a band. The cap at 2 m and the floor at 1 m mean the raw result is only the answer for tankers in the middle breadth range. A designer who applies to a 48 m Suezmax and builds a 3.2 m double bottom under the pump room has over-built; the cap holds the requirement at 2 m. A designer who applies to a 14 m coaster and builds a 0.93 m double bottom has under-built; the floor lifts the requirement to 1 m. Both errors come from forgetting the bounds.
The third pitfall is the “at any cross-section” reading. The protective distance has to be met across the whole pump-room bottom, including any step in the bottom plating or rise of floor toward the after bulkhead. A double bottom that meets over most of its length but pinches at one frame fails, and plan approval is built to catch exactly that local minimum. The fourth is misreading the exemption. It is not a general waiver but a specific functional demonstration tied to a pumping arrangement that survives flooding, and it has to be designed in from the start, not claimed after the fact on a conventional pump room.
Limitations
Regulation 22 protects against bottom penetration, not side penetration. A collision that tears the side shell at the pump room is outside its scope; that risk is addressed, if at all, by the side protection of the double hull and by the outflow performance of Regulation 23, not by the pump-room double bottom. The rule also says nothing about the height of the pump-room bottom relative to operational flooding from internal sources, leaks, or firefighting water; it is a grounding-protection measure, and its clearances are set against a bottom contact, not against an internal casualty.
The dimensional requirement is a minimum, and a minimum sized by a simple breadth formula rather than by the specific grounding energy a given ship and trade present. A tanker that habitually loads to deep drafts in shallow, rock-strewn approaches faces a higher bottom-penetration exposure than the formula contemplates, and Regulation 22 doesn’t scale to that exposure. The 2 m cap in particular means the largest tankers carry the same protective distance as mid-size ships, which is proportionate by the convention’s own logic but isn’t a claim that 2 m is sufficient for every grounding a VLCC might suffer.
The rule binds only oil tankers of 5,000 tonnes deadweight and above constructed on or after 1 January 2007. Smaller tankers, and the large existing fleet built before that date, carry no mandatory pump-room double bottom under MARPOL, however much their trading risk might argue for one. The protection is a newbuilding feature; it can’t be retrofitted into an existing ship without major structural rebuilding, so the population of protected pump rooms grows only as the fleet renews. Finally, the exemption shifts the assurance from a verifiable structural dimension to a design demonstration that flooding won’t disable the pumps, and the quality of that assurance depends on the rigor of the plan-approval review, which varies between administrations and recognized organizations. The double bottom you can measure; the surviving-pumping-function claim you have to trust the approval of.
See also
The pump-room rule sits inside the wider oil regime of MARPOL Annex I under the parent MARPOL Convention. Its closest structural relatives are the double-hull requirement of Regulation 19, the accidental-oil-outflow performance of Regulation 23, the segregated-ballast and protective-location rules of Regulation 18, and the damage-stability standard of Regulation 28. Compliance is confirmed at flag and class survey and cross-checked under port state control.