Cable in CFAST

[Rumi27]

Hi,
In a project for reproducing fire scenarios it is required to analyze the cable during fire and also cable as a fire source.
Therefore, can you please help me if someone had experience in dealing with a cable in CFAST or it is not possible completely.

1. to show the cable itself and its behavior during fire
2. showing cable and making it as a fire source.
   would be very grateful for your suggestions.
   Thanks

[mcgratta]

A cable can be modeled as a cylindrical target, assuming you know its thermal properties. That can give you a prediction of the cable's surface temperature. As for burning, you simply specify a heat release rate curve. CFAST does not predict the burning rate.

[Rumi27]

A cable can be modeled as a cylindrical target, assuming you know its thermal properties. That can give you a prediction of the cable's surface temperature. As for burning, you simply specify a heat release rate curve. CFAST does not predict the burning rate.

Thank you very much for your reply.
Just to clarify, since the cable can be represented as a cylindrical target in CFAST, does this mean we cannot visually show the actual cable geometry, but instead only treat it as a point/target? If the cable extends over some length, should we then assume that the predicted surface temperature from the cylindrical target model would be applied uniformly along the entire cable length?

Thanks again for your helpful explanation.

[mcgratta]

Yes, the cable is exposed to the uniform temperature of the layer where it resides.

[drjfloyd]

In CFAST the target heat flux is convection+radiation from the layer plus radiation from the fire (see 5.1.5 in the CFAST Tech Ref). The layer flux is constant throughout the layer since the layer has the same temperature. The fire flux is a function of the distance from the fire. You can define multiple targets in a room.

[rpeacoc]

There's also radiation from the compartment surfaces that impact target temperatures

[Rumi27]

Thanks, that helps a lot.

To make sure I’m modeling the cable correctly in CFAST:

Uniform layer exposure — My understanding is the convective/radiative exposure from the hot gas layer is uniform within a layer, and the fire radiation term varies with distance to the fire. So to approximate a cable run, I should place multiple cylindrical targets along the tray/path to sample the local fire-radiation term. Is that the recommended approach?

Cylindrical target details — For a cable of diameter D, I’m setting TYPE='CYLINDER' and TEMPERATURE_DEPTH = D/2 to track the centerline temperature; with cable emissivity via EMISSIVITY in the material block. Is that correct?

Orientation/shielding — If the cable is on a tray or close to a wall, does setting SURFACE_ORIENTATION (e.g., FLOOR, LEFT WALL) affect the radiative view factors used for the target, or is target radiation handled independently of that flag?

Cable as a fuel — If the cable/bundle becomes the fire source, I plan to keep the cylindrical targets for thermal response, but define a separate &FIRE with the HRR(t) for the bundle. Any pitfalls to watch for (e.g., double counting radiation to the target located near the fire)?

Validation references — Are there specific validation/benchmark decks you recommend for cable/target heating (e.g., WTC spray burner, NIST/NRC target heating) that best illustrate target setup?

Finally, I realize CFAST/Smokeview won’t `show the cylindrical targets (running example NIST_NRC_T18.in) ; I’ll rely on the spreadsheet outputs for target temperatures/fluxes. Just checking I’m not missing a display option.

Thanks again for the guidance.