A cable transit can carry the right fire rating and still be unsuitable for the opening shown on the drawing. The difference may be the supporting structure, the cable diameter or a detail of the insulation. For oil and gas projects, selecting the seal means checking how the complete installation will perform under the fire exposure identified for that location.
That work starts with the project fire assessment. It should establish the required barrier function and duration of protection, taking account of credible fire scenarios. A penetration beside pressurised process equipment may face different conditions from one serving an electrical room. The penetration specification needs to reflect those local conditions. The assessment should also identify which side of the division may be exposed.
A-class and H-class ratings describe performance under different fire exposures. A-class testing uses the standard fire curve, while H-class testing applies a hydrocarbon curve with a more rapid temperature rise and higher test temperatures. The number attached to the classification identifies the insulation period. An A60 rating therefore cannot establish suitability for an H60 requirement.
Evaluating resistance to jet fires
Jet fires introduce a further consideration. An ignited release of pressurised hydrocarbon can direct a flame onto a local area of the division. Intense heating and mechanical action challenge exposed insulation and interfaces. Where this is a credible scenario, engineers need appropriate jet-fire evidence, including the test conditions and acceptance criteria.
ISO 22899-1 provides a method for evaluating resistance to jet fires. Its results contribute to the fire assessment for the intended application. Jet-fire testing complements hydrocarbon fire resistance testing; it does not replace it. Where both exposures form part of the design basis, the supporting evidence needs to address both.
The assessment must also follow the complete penetration through the structure. In a modular transit, the frame, sealing blocks and compression components work together. Their performance depends on the surrounding division and the specified insulation. A material flammability classification, on its own, cannot establish the fire resistance of that assembly. Approval for a welded frame should not be assumed to cover a bolted installation.
The published ABS design assessment for MCT Brattberg’s RGS system illustrates this relationship. One J120 arrangement uses a 300 mm back-to-back frame and specifies maximum marine cable and metallic pipe diameters of 110mm and 30mm respectively, with a defined insulation arrangement. Those dimensions belong to that configuration. They should not be transferred to another arrangement simply because it carries the same system name.
The importance of insulation
Insulation deserves particular attention during design coordination. Its thickness, extent and attachment must follow the approved detail. Space around the opening must accommodate that detail once cable trays, pipe supports and neighbouring services are installed. If the insulation cannot be fitted as specified, the discrepancy needs resolving before the penetration is accepted.
Consider a cable tray positioned close to a bulkhead. The transit may fit neatly into the available opening, yet the tray can obstruct access needed to complete the insulation. Moving the tray during design is straightforward compared with altering a finished installation. Reviewing the penetration in section, as well as in plan, helps reveal this type of conflict.
Cables and metallic pipes also carry heat through a division. Their construction and dimensions therefore matter to the assessment, even when the opening is completely sealed. Substituting a different pipe material or increasing a cable diameter needs checking against the approval. Geometric fit alone does not demonstrate equivalent fire performance.
A holistic approach
Fire resistance must also be distinguished from gas and water tightness. A pressure test provides evidence about leakage under its stated conditions. It cannot demonstrate resistance to fire. Where a barrier has several protective functions, the specification should identify the evidence required for each, including any requirement to withstand combined or sequential exposures.
During installation, the approved drawing should be available alongside the manufacturer’s instructions. Checks should confirm the actual cable and pipe dimensions, correct components and completion of the compression procedure. Insulation should be inspected before adjacent work conceals it. Assigning responsibility for these checks prevents uncertainty between the structural, electrical and insulation contractors.
The completed record should identify the penetration and connect its installed arrangement to the applicable approval. Photographs help show details that become difficult to inspect later. When cables are subsequently added or removed, that record provides a basis for checking the revised configuration and confirming that the specified protection has been restored. Changes in cable routing can also affect access to insulation around the opening.
A useful final review is to place the approval drawing beside the installation drawing and account for every difference. Resolve deviations with the manufacturer and the relevant approving authority before accepting the work. That gives the operator a documented basis for the barrier’s intended performance.
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