How to calculate the fill rate of the A-60 cable penetration sealing module ?

In our years of experience manufacturing cable and pipe sealing modules, we’ve learned that most projects fail not because of substandard products, but because of flawed selection criteria. There are essentially three things to consider: the sealing grade must not be lower than the penetrating section; the fill rate must not exceed the coverage specified in your certificate; and the certificate’s scope of application must cover your actual installation method. If any one of these three things is wrong, the entire installation will require rework.

According to a publicly reported case from the maritime authorities regarding a ship safety inspection (PSC) case: A vessel’s bridge had five cables with a diameter of at least 5 cm running through a Class A fire-resistant partition deck. The sealing material was ordinary civilian-grade expanding foam—flammable and lacking fire resistance. The inspection determined this to be a serious defect, and the vessel was detained according to law. The detention was only lifted after rectification according to Class A-60 layered and dense sealing procedures and a subsequent successful re-inspection.

This isn’t about “buying the wrong material,” but rather that no one told him during the selection phase that this location belongs to a Class A partition pipe. The most common problems in the application of A-60 fire-resistant cable penetration sealing modules occur at this stage: in the penetration list we reviewed, the vast majority weren’t due to product defects, but rather because the product’s stated applicable scope didn’t match the actual installation method on site.

The following guide follows the actual workflow we use when creating penetration lists for clients: Determine the grade → Determine the insulation side → Calculate the fill rate → Match components → Verification certificate → Add additional requirements → Prevent failures → Submit materials. After reading this, you will have four things: a four-grade conversion table, a fill rate calculation method, a 7-field certificate verification checklist, and a self-inspection checklist for 6 failure points.

Key points

• • The insulation grade can only be increased, not decreased. When an A-60 module is used on an A-0 partition, the module body and the surrounding partition of at least 200mm must be insulated according to A-60 standards; when an A-0 component is used on an A-60 partition, no amount of additional insulation will be acceptable.
  • three sets of standards for the certificate value: 30%, 40%, and 40%. 30% is the upper limit recommended by domestic industry standards, while approximately 40% originates from the older IMO recommendation system. Only the specific product certificate value will be binding on your particular model. These three standards are not interchangeable.
  • A certificate has 7 fields : type, number and holder, applicable separation, whether the level is explicitly listed, installation method, restrictions, validity period and production supervision.
  • Fill factor is not the only geometric constraint. Maximum cable outer diameter, bundle location, and inter-cable filler thickness are three other independent conditions.
  • Fire resistance, water tightness, and air tightness are three sets of evidence. A water pressure test cannot prove 60 minutes of fire resistance.

Next, Nico from TST Seal will discuss with everyone how to calculate the fill rate of a sealing module.

formula

The design value is 25%–35%, and the final verification will be based on the certificate you have. 30% is the upper limit recommended by domestic industry standards, and about 40% is a value often cited under the old IMO recommendation system. Only the certificate value is binding on your model. The three numbers come from different sources and are not interchangeable.

Fill rate (cable occupancy rate) = Sum of total cable cross-sectional areas ÷ Inner cross-sectional area of the conduit:

Fill rate = Σ(π × r²) ÷ (π × R²) × 100%

Note what it overlooks: cable deformation under pressure, bending radius, and the physical clearance required by the module itself. Therefore, it’s only the first round of dimensional verification; the frame specifications must be finalized after passing the two red lines below. See the fill rate calculation examples for other aperture sizes for examples of other aperture sizes .

A complete example

The inner diameter of the sleeve is 150 mm, and the inner cross-sectional area is π × 75² = 17,671 mm² .

150mm conduit fill ratio: Four cable configurations and judgments

Source: This table is calculated using the formula. The cable area is calculated based on the circular area of the nominal outer diameter; the actual area should be verified against the true outer diameter in the cable list.

In addition to the fill rate, there are two separate red lines:

• • Maximum cable outer diameter. A large enclosure allows for a high fill factor, but this does not mean that a single cable can be thick—the certificate sets a separate upper limit for the outer diameter for each enclosure size. A Φ48 cable will not become compliant simply because its fill factor is only 12%.
  • Spacing and bundling position. The certificate requires the cable harness to be arranged in the center of the conduit; the standard requires a minimum filler thickness between the cable and the frame wall, and between cables, generally not less than 8mm. Even if the filler ratio meets the standard, if all the cables are squeezed to one side, it is still a non-compliance.

Why do 30%, 40%, and certificate value exist simultaneously?

Where do the three fill rate values come from ?

Source: CB/T 3386.1; IMO Res. A.754(18) system (commonly cited in the industry); product certificate. Fill rate varies by model, please refer to the certificate in your project file.

Another easily confused value: the conduit coefficient (total cable cross-sectional area / conduit cross-sectional area) for CCS inspection should not exceed 0.4 . The physical quantity is the same, but the name and limit are different, and it will appear on the inspection list—0.4 and 30% are not the same thing.

Here’s a tip: Design based on 25%–35%, verify based on the certificate you have, and treat 30% and 40% as background rather than authority.

What happens if the standard is exceeded?

The more tightly packed the wires, the stronger the seal will be. Overcrowding will reduce the volume of insulation and expansion that the fire resistance test relies on, causing the unexposed side to heat up faster. The insulation criterion will fail before the integrity criterion fails—the whole system will fail, but it will still block the fire. Dense wire harnesses will also conduct heat along the copper core axis, so failure often manifests as localized overheating at a distant point, rather than an overall temperature rise.