Cargo Fires

[bsevenfour]

Just wanted to get some feedback on what policies or opinions you might have concerning Cargo Fires. For the sake of this discussion I am assuming that your aircraft is fitted with cargo fire extinguihers.

On the Boeing it is said that an uncontrollable cargo fire will burn through the hull in 20 mins. Obviously the target would then seem to be to land within the 20 minute timescale. However for anyone who has flown transatlantic or transpacific knows this is often impossible. What then do you reckon you should do if landing within this 20 minute timescale is not possible ?

Here might be some of the conflicting viewpoints.

- If a long distance from nearest airport you have got to assume that the fire extinguishers will deal with the fire. By assuming this you can stay high and therefore with the hopefully higher winds and TAS aloft you can proceed to your destination in the shortest possible time.

- If you have a cargo fire you have to assume the worst i.e. that the fire will burn through within 20 mins. Therefore you should descend and if you are not going to make it to an airport within 20 mins. you should make preparations to ditch. After all you might have some of surviving a ditching but none if the aircraft fails structurally at 35,000 feet.

Which side do you come down on ?

Following on from this do you really think the cargo fire warning systems fitted to many aircraft are sufficient. The ones fitted to Boeings are usually photoelectric cells. But these are not going to tell you if the fire has been extinguished. Added to this they have been known to give false alarms at times. Does any aircraft out there have cameras fitted for the cargo compartments ? After all it would certainly be an invaluable source of information in the above scenario.

[G.Khan]

Well, an UNCONTROLLED fire may burn through in twenty minutes but if the fire extinguishers work then you will have supressed the fire and in mid Atlantic could hopefully make a safe landing before the supression expires.

If the fire extinguishers fail to act then, I suspect, most would say ditch, mid Pacific not a very comfortable option.:(

Do we have an argument for applying ETOPS type rules to trans Pacific freighters?:confused:

[bsevenfour]

Your answer raises a key point and is the reason why I raised this topic.

How do you know whether the fire is under control or not ?

Let's say you discharge the extinguishers and they discharge normally how do you know that the fire is therefore under
control ? For an engine fire you usually get an indication that the fire is extinguished and if in any doubt you can always take a look assuming your engines are wing mounted. This is not the case with a cargo fire, not on any aircraft I've flown. Indeed on the 747 classic they specifically mention the fact that when the second round of extinguishers are discharged the cargo fire warning may illuminate again ( Not very reassuring)!! I realise that with most cargo compartments you can reduce the airflow to them to aid the work of the extinguishers and as a result the chances of the fire surviving are slim but is there not always that chance nevertheless ? And if there is where does that leave you having assumed that because the extinguishers discharged the situation is under control and you can fly on ?

Does anybody know of or can direct me to an article on this subject which maybe can alleviate some of these doubts ?

[QAVION]

"Does any aircraft out there have cameras fitted for the cargo compartments ? After all it would certainly be an invaluable source of information in the above scenario. "

I'm not sure that cameras would be all that practical "bsevenfour": These are only going to see what the smoke detectors are going to "see". i.e. The very confined airspace above the cargo pallets and below the ceiling (ie. a few inches). In such a confined area, there would have to be several cameras per area... and lighting would have to be enabled in the cargo area in flight for you to see anything (In flight, power is removed from a lot of electrical devices in the cargo area... which in itself reduces the chances of a fire being started. Adding bright lights and cameras increases this risk).

On a 747-400 (for example), there are literally dozens of smoke sampling ports in the roof (offering far more coverage than one or two cameras could). Because the cameras would have to be located in the area where the smoke would generally gather, the fumes may permanently coat the lenses with an opaque film which may be useless for viewing purposes later on in flight. Even before the smoke has formed, probably the condensation which is typical in cargo areas, deisel fumes from cargo loaders, etc would quickly reduce the clarity of the camera's picture over a relatively short period of time.

It's interesting to hear that the second discharge of extinguishant triggers false alarms. False alarms are also triggered by disinsection devices being set off. Would it be possible to tell the difference between whisps of smoke, mists of fly spray and extinguishant even in a brightly lit confined area with cameras?

Regards.
Q.

[Young Paul]

At risk of stating the obvious, the concentration of effort has been on reducing the risk of cargo fire, or containing its effects. Hence the dangerous goods regulations, and training for Customer Services, and rules on what passengers carry. That's the main defence.

Once you actually have an uncontained cargo fire - as with an uncontained engine failure and fire which can damage the wing structure, or uncontained fire in the cabin - you do have limited time available. It's for situations like this that captains are paid their salary. Fortunately, the frequency with which it happens is about the same, to the best of my knowledge - of the order of no more than one every decade, at a guess?

Whilst we might all say that safety has no price, the fact is that all risk analysis has a cost dimension. Perhaps in some circumstances cameras in the hold would help - as they might directed at the engines and in the cabin. However, until the benefit (perhaps one accident in six or seven years) outweighs the cost (? £10000 per aircraft, plus the cost of reengineering pilot procedures), it won't happen. Bear in mind that the cost would have to be passed on ultimately to the people paying for the aircraft to operate - freight shippers and passengers. Don't blame the airlines - ultimately, what price are the fare-payers prepared to pay for safety?

[purr]

on longer flights one bottle is fired at once then another bottle is fired which discharges at a slower rate in a manner that it empties
in 1 hours time. (ETOPS):p

[Ze German]

Vot about zer infra rot kameras? Surely zis vould be more benefishial zan video vuns!

[quid]

Given the actual number of hull losses due to cargo fire compared to the actual number of false warnings, I doubt if many would choose to ditch over the middle of the Atlantic due to a warning.

[*Lancer*]

If you had an uncontrollable cargo fire that was burning through the hull with structural failure imminent, wouldn't there be enough indications within the cabin to determine the fact?

[RatherBeFlying]

Forest Protection Industries based on Sproat Lake in British Columbia have a device that might (with a bit of engineering) help. They have developed water pickups for their Martin Mars firebombers that enable them to pick up water from lake surfaces on the fly.

Now all you have to do is engineer these pickups for Vref+20 and figure out how to run a pickup in mid-ocean -- and your oceanic cargo fire problem is solved:D

[Tinstaafl]

If the the fire was still going after firing the bottles then I'd depressurise.

As long as the fire wasn't getting it's oxygen from an on board oxidant the reduced oxygen will retard & possibly extinguish the fire.

[Checkboard]

Depressurise, and presumably stay at altitude, Tinny?

You'll be timing those pax oxy systems then, to allow enough for the rapid descent - and crossing your fingers against the bends then?

For me:

Fire warning.
Swear.
Fire Bottle.
Call Cabin Manager & inform them of the problem, ask them to station a FA over the hold position to check for smoke from the windows / heat in the floor etc.
Fire Second bottle if necessary
On report of conditions worsening:
Start ditching drill in cabin
Descend to lowest safe to sight sea surface, and be ready to ditch at minimum notice.
If fire not out / conditions in the cabin worsening - ditch.

[bsevenfour]

As I had hoped some interesting responses.

QAVION: The smoke detectors on the 747-400 I am familiar with aren't quite so numerous. Each cargo hold has two dual loop detectors both of which must sense a fire for a warning to be given. The system on the earlier aircraft had a potential flaw in that if one loop failed the sensor would not reconfigure to single loop operation and as a result if a fire was occuring that particular detector would not signal a fire warning. There are of course two of these detectors in each cargo compartment so the chances of both experiencing a single loop failure on a flight on which you also had a cargo fire are so small as to be insignificant. On the newer aircraft if one loop senses a fire the other loop is automatically checked and if it is serviceable a fault message is generated for the loop detecting the fire. If it fails the test a fire warning is given.

LANCER : If you are waiting for some structural failure to be the first sign that you have an uncontrolled fire in the cargo bay then it will probably be too late for any action to be taken assuming you take the first option in my orignal post and decide to stay high confident that the fire extinguishers have worked.

TINSTAAFL : An interesting suggestion however while you may increase the cabin altitude in order to protect the passengers passenger oxygen would have to be selected on. Would this meet your requirements for an onboard oxidant ?? The checklist I follow for cargo fires requires you to manually select the landing altitude to 8,000ft. This will depressurise the aircraft partially. The benefit of this is that you obviously achieve a reduction in O2 supply to the fire plus a reduced ventilation rate but you don't have to worry about Pax O2 supply. This means you can stay high and as a result have a higher TAS.

CHECKBOARD: A good suggestion re getting feedback from the cabin and feeling the floor. Definitely a good idea. Going on from this idea, as a defence against false alarms, I think checking the cargo compartment temperature would be a worthwhile step also. Not that a low temperature would stop you from running the checklist and discharging the extinguishers but it coupled with the fact that the floor is not hot could be just the information you need to give you confidence in staying high depressurising the cabin to the max landing altitude, such that pax oxygen not required, then proceeding to the nearest airport at your cruising level thus gaining from a higher TAS.

Every situation is different. When in the middle of the Atlantic or the Pacific and you get the fire warning message the first step is to obviously run the checklist. This would in most cases involve firing the extinguishers, reducing the airflow to the cargo compartment and increasing the cabin altitude. Following this after you have talked to ATC and got established direct to the nearest airport the next step I believe should be information gathering from all available sources to establish if the fire is for real and if so how bad is it. Again as mentioned above input from the cabin and checking the cargo temperature can give you invaluable information. If the situation is not improving but shows signs of diminsihing i.e floor getting hotter, smoke appearing my next step would be a descent to 14,000ft and complete depressurisation. By going to this level you should again forgo the need for passenger oxygen although crew oxygen should be used. This futher depressurisation will again achieve the twin blows of reducing O2 supply to the fire and reducing the ventilation rate through the cargo compartment. By descending to this level and not lower you keep to a minimum the TAS decrement from higher altitude cruise. At this level I would also review the ditching checklist accomplishing as much as I could. If feedback still indicates the situation diminishing I would then descend for a ditching. The only modification I would make to this is if feedback indicated a rapidly deteriorating situation I would skip the step at 14,000ft. I believe this plan of action would offer the best compromise between staying high and getting to the airport ASAP but risking a structural failure if the fire is still burning and descending for a ditching and the consequent dangers associated with it.

Comments ? Additional suggestions ?

[tired]

Good discussion this, one of the many advantages of having a site like Prune!

I'm with Checkboard on this one - fire the bottle, stay at altitude and head for the closest runway. Station an FA in the affected area and if he/she reports that the floor is getting warm/er, or any other indications of a deteriorating situation, then head for the surface and prepare to ditch. I suppose you could stop at F140 and depressurise as bsevenfour suggests, but I'm not convinced that would help all that much. Fires can and do burn at altitudes much higher than 14 000' on the ground (and in the air - ask a WW2 bomber pilot), so I feel that you're kidding yourself with the stop at 140 - rather get down and prepare for the worst.

As a matter of interest, on the A340 the 2nd fire bottle discharges over a 4 hour period which does provide a some comfort if you're a long way home. Always assuming that the 1st bottle has more or less killed the fire, of course. :(

[mono]

Lets try to be rational here.

All ETOPS/long range a/c have their cargo fire protection systems certified to supress a cargo fire for anything up to 195 mins and more. If in the event of, for example, a fwd cargo compartment fire on an ETOPS 767, here's what happens.

2 remote smoke detectors have cargo compartment air drawn through them from ports located at numerous locations in the cargo bay. If they both detect a fire condition, the appropriate push button switch on the flight deck illuminates along with the fire bell and EICAS warning. At this point the fire switch is pressed. This action causes several things to happen :-

The supplimental cargo heating system shut off valves close preventing fresh air from reaching the area.

The left and right recirculation fans shut down stopping smoke/toxic air being re-introduced back into the cabin and further reducing cargo bay air circulation.

The fire bell stops (if not previously done)

The overboard exhaust valve opens (a secondary effect of the recirc fan stopping) to aid smoke clearance and maintain sufficient airflow for equipment cooling.

Galleys are load shed.

All the cockpit lights go full bright (possibly to improve visibility in smokey conditions)

A circuit is made to enable firing of the extinguishant.

If the crew now press the discharge button, one bottle containing 80lbs of halon is discharged into the cargo bay (when you remember that halon is a gas, 80lbs is an awful lot of suppressant).

Irrespective of whether the fire has been extinguished or not (and it should have been with that amount of halon 1301) after 30 minutes a further 113lbs of halon 1301 is metered into the cargo bay over a period of around 2 1/2 hrs to provide 195 minutes of fire suppression.

If the a/c lands within 30 mins of firing the first bottle the second bottles are fired automatically on landing

Halon 1301 is a heavier than air gas, what it does when discharged is to fill the cargo bay from the floor up pushing up the air and therefore removing the oxygen supply from the fire. It is colourless and as such should not affect the correct operation of the smoke/fire detection system. (As an aside if you suspect a collegue to have collapsed due to halon inhalation the correct remedy is to invert him/her and the halon literally falls out of the lungs).

This is a brief technical description of the 767 180 min ETOPS cargo fire suppresion system. The 757 is similar but with less halon used due to smaller cargo bays, and I imagine most other long range a/c would be effectively the same with minor variations for type.

Of course on the 767 if you want to be sure you can always have a look!
'Cos it is possible to enter the cargo bays from within the a/c. However as this is a public forum I won't go into that
;)

For me then were I a pilot (hey I only fix 'em) I would follow the SOP and blow the bottles and continue to the nearest airport and trust the a/c systems to do the job. If I got another fire warning, either in the same compartment, or another however, then that would be another thing all together.
:eek:

[QAVION]

"The smoke detectors on the 747-400 I am familiar with aren't quite so numerous. "

BSeven4...
Actually, I was talking about sampling ports, not detectors here (see Mono's answer). ;)

There is a network of pipes above the cargo area with soft plastic tubes protruding into the cargo area. The air is drawn through these towards the limited number of smoke detectors. There are actually 8 detectors on the lower deck:
A&B detectors for the fwd part of the Forward Cargo (8 sampling ports)
A&B detectors for the aft part of the Forward Cargo (8 sampling ports)
A&B detectors for the Aft Cargo (10 sampling ports)
A&B detectors for the Bulk Cargo (6 sampling ports)

There are four discharge points in the Fwd Cargo and there are 6 extinguisher discharge points in the Aft Cargo (the bulk has to make do with the extinguishant being discharged in the Aft Cargo). The relationship between the bottles and the discharge points is best shown with a diagram. Please let me know if you would like a copy.

Cheers.
Q.

[bsevenfour]

QAVION, you are absolutely correct. Sorry I misread your original post and obviously thought you were talking about detectors.

Following on from this discussion another question to throw out there for comments and discussion. I'm not sure how it applies to the Airbus as I don't know how the detection system works (hopefully somebody type rated may be able to enlighten me). The question is as follows : The detection system on the 747 ( and from mono's post seemingly the 767 and 757) relies on bleed air flow to draw in air from the cargo compartment for sampling. What if for some reason this bleed air flow failed or had to be switched off e.g. if you have a centre bleed duct leak on a -400 you have to isolate that portion of the duct and as a result you lose the bleed air flow. What would be your actions now that you no longer have any cargo fire protection ?

-Continue as normal and hope by the laws of probability you should be alright.

-Go through the fire drill on the presumption of the worst case scenario. This would involve on a Boeing taking steps to reduce the O2 supply to the cargo compartment, reducing the vetilation rate and firing the extinguishers. After this proceed to your nearest suitable airport.

-Same as above but continue on to your destination.

-Go through the precautionary measures to reduce O2 supply and ventilation rate of the cargo compartment but stop short of firing the bottles. Alert the cabin crew in the applicable part of the aircraft to be on the lookout for anything that may indicate the presence of a fire. Continue to the nearest suitable airport.

-Same as above but continue on to your destination.

(Sorry if this brings back bad memories of the CAA multiple choice exam but I think the best way to encourage discussion is put as many options out there as possible)

I would also like to expand this question to any ETOPS operators out there. On a transatlantic or transpacific flight with a similar failure of a fire detection system but this time for one of your two engines what would be your actions ?

[QAVION]

"The detection system on the 747 ( and from mono's post seemingly the 767 and 757) relies on bleed air flow to draw in air from the cargo compartment for sampling. What if for some reason this bleed air flow failed or had to be switched off e.g. if you have a centre bleed duct leak on a -400 you have to isolate that portion of the duct and as a result you lose the bleed air flow. What would be your actions now that you no longer have any cargo fire protection ?"

Loss of vacuum is sensed by a pressure switch and an Advisory message "}CARGO DET AIR" and an associated Status message is generated on your EICAS displays.

If you had these messages pop up on departure (and the switch was proven to be operating correctly), you would not be allowed to proceed unless your cargo bays were empty.

As for what to do in the air.... I guess this is the part where you start earning your money :D

It would probably come down to probabilities. What are the odds of you having to isolate the Centre manifold and having a cargo fire. Come to think of it, having to isolate the Centre manifold is already pretty serious, isn't it?

Any help?

Cheers.
Q.

[mono]

Bseven,

Just a quick point here, I can't speak for the 747 (any type) but the 757/767 have separate smoke detector fans (2 per cargo bay/detector pair) to draw the cargo bay air through the detectors. Only one is running at any time. A plenum pressure switch senses failure of one of the fans and will automatically start the second fan, so a dual fan failure on this type will cause loss of smoke detection. This will of course produce the relevant EICAS status/advisory for QRH action. Bleed air is NOT the air source for the detectors as it may in itself be contaminated.

[bsevenfour]

Mono,

The system on the 757/767 is obviously different to the 747 system. In the 747 system the bleed air is not in itself passed through the sensors for obvious reasons which you refer to. Instead the flow of the bleed air is used to create a vacuum which draws in the air from the cargo compartment through the sampling ports. It is this air which the detectors check.

From what you say it sounds as if the system on the 757/767 is better than on the 747 as at least you have some form of redundancy.

So what would you do Mono if you had a twin fan failure while making your way across the Atlantic / Pacific ? And come to think of it what about a failure of your engine fire detectors if you're on an ETOPS sector, probably a more critical failure ?

[bsevenfour]

I'd just like to revive this subject again of fire detectors failing. Once again :

On a Transoceaic sector what would you do if your cargo fire detection system failed ?

For ETOPS aircraft an additional question. What would you do if your fire detectors on one engine failed ?

I have made some possible suggestions four posts ago to generate some discussion on the cargo fire detector side of things. I cannot however talk about ETOPS as I'm not familiar with ETOPS operation but would be interested to hear any replies on the issue.

[Kurtis Chukle Willis]

Old subject I know but am interested if anyone has any opinions on the matter,all thoughts appreciated