B737NG Cargo Fire Light

[framer]

Hi there,
If you have experienced a cargo fire and subsequently discharged the extinguisher into the bay and the cargo fire has successfully been extinguished, will the light remain illuminated due to the extinguishing agent or will it go out?

[latetonite]

Based on simulator experience, it should go out.

[de facto]

As long as there is no smoke detected,the 'fire' light will be extinguished.

[framer]

Thanks for that.
I think you're probably right but I can't find it written anywhere. Does anyone know a reference?

[Tom!]

FCOM2 Ch8
Illuminated (red) - • at least one detector in each loop detects smoke •
with power failed in one loop, at least one detector on the remaining loop detects smoke.

[Best Rate]

I can't say it definitively, but I find it hard to believe the light would extinguish all that quickly given that the photo-electric sensors would still register smoke/steam from the smouldering material for a period of time after suppressant released into the compartment... (Might just ask an engineer!)

There doesn't seem to be any references to timing of the FWD or AFT cargo fire lights 'extinguishing'...

[de facto]

framer Thanks for that.
I think you're probably right but I can't find it written anywhere. Does anyone know a reference?

Trust me

[framer]

Ha ha you and I would both be dead if we trusted people we didn't know

[framer]

I can't say it definitively, but I find it hard to believe the light would extinguish all that quickly given that the photo-electric sensors would still register smoke/steam from the smouldering material for a period of time after suppressant released into the compartment

I am of the same mind as Best Rate.
The photo-electric cells detect smoke apparently and also there is heat detection which is triggered at 110degrees C.
This from a -800 Engineering manual.

Functional Description

The filter drier meters the halon gas so that the halon level in the compartment stays above 3% for 195 minutes. The filter drier uses desiccant granules to remove moisture. It has a filter to remove squib debris or other contaminants to prevent line blockage.

So my question becomes;
Is 3% Halon detectable as smoke to the photo electric cells?
More thoughts please ( or better yet, a reference that says the light will extinguish).

[de facto]

The smoke is detected by 6 smoke detectors in the aft cargo and 4 in the forward cargo hold.
When the detectors detect smoke they send a signal to the Cargo Electronic Unit which then triggers the fire alarm bell and the Fire light.

The photo-electric cells detect smoke apparently

Obviously

Is 3% Halon detectable as smoke to the photo electric cells?

Try it at home and let us know,i doubt it though.

More thoughts please ( or better yet, a reference that says the light will extinguish).

No prob stranger...
Boeing AMM Cargo Smoke Detection System Operation 26-10.
As with an advisory condition, as long as a warning condition exists, all visual annunciations on the control panel will remain illuminated. When the fire warn- ing condition is no longer present, all annunciations will extinguish, and the sys- tem will automatically reset itself to normal mode of operation.

[framer]

Good stuff, that's for your help

[de facto]

Quote:
Is 3% Halon detectable as smoke to the photo electric cells?

From Boeing:

Photoelectric-area type. These detectors are designed to detect the presence of smoke particles in the air by reflection of scattered light. They also rely on particles in the air being convectively carried into a sensing chamber where light from a pilot lamp is transmitted through a sensing chamber. If smoke is present, it will reflect light onto a photocell and trigger an alarm. [B]
Newer production airplanes use photoelectric detectors based on an advanced smoke sensor utilizing two discrete wavelengths to determine the presence of smoke and to distinguish between smoke and nonsmoke aerosols. These are also mounted in the ceiling or upper sidewalls of the protected space.

Here is the source since you dont know me: Fire Protection: Passenger Cabin

[framer]

Here is the source since you dont know me:

Heh heh, thanks de facto.
I am now comfortable that you were spot on at the start of the thread in that it will go out if the conditions cease.
Cheers.

[latetonite]

Framer, how would you otherwise know when to go the the 'land ASAP' and 'get the gear down-and-dial-in-an-ILS' situation?

[framer]

Framer, how would you otherwise know when to go the the 'land ASAP'

I'm not sure I understand you latetonite, if I have had the cargo fire warning light come on I certainly won't be carrying on past good airports even if it does go out.

and 'get the gear down-and-dial-in-an-ILS' situation?

I don't know what that means sorry.

[latetonite]

That is what you do when you are on fire. The QRH does not cover everything.

[framer]

Thanks for the advice. I'll keep that in mind

[EEngr]

The response of the photoelectric smoke detectors would depend on the concentration of smoke in the cargo hold. This, in turn, would depend on the air circulation through the cargo area.

The design of the fire suppression system is to bring the compartment halon concentration to an initial 5% and maintain it at 3% for the time needed to divert (60 min/180 min for ETOPS). So the need to maintain a minimum halon concentration would contraindicate any ventilation that would clear smoke and the detectors' alarm condition.

Depending on the naturer of the smoke, it might hang around for some time (along with the alarm condition) after the fire was extinguished. If the smoke source was initially localised, it may dispurse on its own throughout the hold and drop below the detector threshold more rapidly.