Retrofit BWTS for Tankers: Explosion-Proof Requirements
Updated
A BWTS retrofit on an oil or chemical tanker must respect hazardous-area classification: equipment in the pump room and adjacent zones must be certified explosion-proof (Ex), electrolysis systems generate hydrogen that must be managed, and hot work requires gas-freeing under strict permits. These requirements add cost and constrain installation method, so equipment selection and layout must account for hazardous-area zoning from the feasibility stage. Location of the ballast pumps in the pump room is central to the design.
Request BWTS spare parts, annual calibration or ballast-water testing
Key takeaways
- Tanker pump rooms are hazardous areas, so equipment installed there must be certified explosion-proof (Ex) under IEC/IECEx or an equivalent class-accepted standard.
- Ex-rated equipment costs more and has longer lead times, and can decide the technology choice because not all systems offer hazardous-area variants.
- Electrolysis systems generate hydrogen that must be safely vented and interlocked, a requirement scrutinised especially closely on tankers.
- UV systems avoid the hydrogen question, which some tanker owners weigh against their higher power demand.
- Hot work near cargo and pump-room spaces requires gas-freeing under a permit system, which constrains riding-crew work and favours drydock installation.
- A hazardous-area zoning study at the feasibility stage shapes technology choice and layout before any hardware is committed.
Why Are Tanker Retrofits Different?
On oil and chemical tankers the ballast pumps and much of the ballast piping live in the pump room, which is a hazardous area where flammable cargo vapour may be present. Any electrical or heat-generating equipment installed there must be certified for the hazardous zone, and any hot work must be preceded by gas-freeing and controlled under a permit system.
This changes the retrofit from a purely engineering exercise into a safety-driven one. The treatment technology, its location, and the installation method are all shaped first by hazardous-area rules and only then by space and performance.
The consequence is higher cost and tighter constraints than on a dry-cargo ship, but the requirements are well established and manageable when built into the design from the start rather than discovered during installation.
What Does Hazardous-Area Classification Require?
The pump room and adjacent spaces are classified into hazardous zones according to the likelihood of a flammable atmosphere, and equipment installed in each zone must carry the corresponding explosion-protection certification — Ex-rated equipment under IEC/IECEx or equivalent standards accepted by the flag and class. Motors, sensors, junction boxes, and lighting all fall under this requirement.
Certified Ex equipment costs more and has longer lead times than standard equipment, and it constrains which treatment systems can be located in the hazardous area at all. Some systems are designed with hazardous-area variants; others are not, which can decide the technology choice for a tanker.
A common design response is to keep the hazardous-area footprint minimal — placing only what must be in the pump room there and locating control cabinets, reactors, or UV chambers in a safe space such as the engine room, connected by piping. The zoning study, done early, defines what is possible.
How Is Hydrogen Managed on Electrolysis Systems?
Electrochlorination and electrolysis systems generate hydrogen gas as a by-product of the electrolytic reaction. Hydrogen is flammable, so the system includes degassing and venting arrangements to dilute and safely vent it, and this arrangement is a safety-critical part of the design on any vessel.
On a tanker the hydrogen management requirements are especially stringent because of the surrounding hazardous atmosphere. The venting must route to a safe location, ventilation and gas-detection interlocks must be reliable, and the whole arrangement is scrutinised by class as part of drawing approval.
UV systems avoid the hydrogen question entirely, which is one reason some tanker owners favour them despite their power demand. The trade-off between hydrogen management complexity and electrical demand is part of the technology decision for a tanker.
How Does Hot Work and Gas-Freeing Constrain Installation?
Welding, cutting, and grinding near cargo and pump-room spaces are hot work that require the space to be gas-freed and certified safe, controlled under a formal permit-to-work system. This is time-consuming and cannot be done casually, which sharply limits riding-crew hot work on a trading tanker.
The practical result is that most hot-work-intensive tanker retrofit tasks are pushed into a gas-free yard period — typically a drydock or dedicated repair stop — while non-hot-work tasks such as cable pulling in safe areas can be spread across voyages. This tends to favour drydock installation for tankers.
Pre-fabrication ashore is even more valuable on tankers than on other vessels, because it minimises the hot work needed on board in the hazardous environment. The more that arrives ready to bolt up, the shorter and safer the ship-side work.
How Does Vessel Type Within Tankers Vary?
Crude and product oil tankers, chemical tankers, and gas carriers each have their own hazardous-area and cargo-compatibility considerations. Chemical tankers may carry cargoes with different vapour characteristics, and gas carriers have their own stringent regimes, all of which the zoning and equipment selection must respect.
Ballast capacity and pump flow rate on large tankers are high, which drives large treatment flow and favours technologies that draw less power per cubic metre — a point where electrolysis competes well against UV, if the hydrogen and Ex requirements can be satisfied.
The salinity and temperature range of the tanker's trade also matter, as they do on any ship, because they define the type-approved envelope the installed system must cover. On tankers these standard selection factors sit alongside, not instead of, the hazardous-area requirements.
How Should a Tanker Retrofit Be Approached?
Begin with a hazardous-area zoning and feasibility study that defines what equipment can go where, confirms the treatment flow and electrical margin, and identifies the hydrogen management and gas-freeing scope. This study shapes the technology choice and layout before any hardware is committed.
Engage class early, because the explosion-protection, hydrogen venting, and structural aspects all require drawing approval, and tanker approvals are more involved than dry-cargo ones. Class also attends the installation and commissioning to verify the safety arrangements.
Sea Clean AS supports tanker retrofits with hazardous-area-aware engineering and, as an authorized Headway agent, can advise on OceanGuard configurations; for other brands it provides independent, brand-agnostic support. It coordinates with the vessel's class society and does not make claims beyond its authorized-agent scope. North Sea and Norway attendance is 0–24 hours; elsewhere by arrangement.
Frequently asked questions
Does the whole BWTS need to be explosion-proof on a tanker?
Only the equipment located in the hazardous area — typically the pump room and adjacent zones — must be Ex-certified. Designs usually keep the hazardous-area footprint minimal, placing control cabinets, reactors, or UV chambers in a safe space such as the engine room and running piping to the hazardous area.
Is UV or electrolysis better for a tanker?
It depends on the trade and the space. Electrolysis draws less power at the high flow rates large tankers need but generates hydrogen requiring careful venting and Ex compliance. UV avoids hydrogen but demands more electrical margin. The hazardous-area and hydrogen requirements often weigh as heavily as performance.
Can a tanker BWTS be installed by a riding crew while trading?
Non-hot-work tasks such as cabling in safe areas can be, but hot work near cargo and pump-room spaces requires gas-freeing under a permit system, which is impractical under way. Most hot-work-intensive tasks are therefore done in a gas-free yard period, favouring drydock installation.
Why do tanker retrofits cost more than dry-cargo ones?
Because of Ex-certified equipment, hydrogen management, gas-freeing, stricter hot-work control, and more involved class approval. These safety requirements add both equipment and labour cost that a bulk carrier or container ship does not carry.
Sources
Related articles
- BWTS Retrofit Guide for Existing Vessels
- BWTS Retrofit: Drydock vs Riding-Crew Installation
- Electrochlorination BWTS Explained: Electrolysis, TRO Generation and Neutralisation
- UV vs Electrochlorination BWTS: How to Choose
- BWTS Retrofit for Bulk Carriers and Gravity Ballasting
- What Is a Ballast Water Treatment System? Explained
Request spares, calibration or ballast-water testing
Include BWMS brand/model, vessel/IMO number, port/terminal, date/ETA and scope or part numbers. These links prepare an email draft; you must send it yourself.
- Request a parts quote — Sensors, TRO reagents, calibration kits and replacement parts. Confirm compatibility, availability and delivery for your installed system.
- Request a calibration booking — Annual instrument calibration with a calibration certificate for the work completed. OEM instructions, drift or applicable rules may require earlier work.
- Request testing coordination — Arrange sampling and testing with an appropriately qualified party for your IMO D-2, commissioning or other stated purpose.
Authorised Headway agent. Other-brand enquiries are independently reviewed; no OEM authorisation is claimed. Sea Clean is not an accredited laboratory or approving authority. Calibration does not demonstrate biological D-2 compliance. Attendance, testing scope and parts delivery are confirmed per enquiry.