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FIRE SERVICE AND GENERAL FIRE SAFETY TOPICS => Fire Safety => Topic started by: GB on January 20, 2016, 12:41:34 PM
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I have ran a quick CFAST simulation of a room with an interior temperature of 2C, outside 20CC and compared it with 15C inside and 20C outside and found no significant difference in the neutral plane - has anyone looked at smoke development in cold rooms and found anything to contradict or confirm the zone model's findings?
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I haven't looked at the neutral plane but the smoke cools more quickly due to cold air entrainment and the cold surfaces it contacts and low level smoke logging is a little quicker in chillers and freezers. I would recommend running a CFD simulation to see the effects. The cold air blowers, if they don't shut down, may affect smoke movement also.
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I once read a Fire Strategy that claimed you would never get a fire in a cold store because of all the ice...!
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Fishy I would argue through instinct only that the fire loading relating to the contents in a freezer at -22C is likely to be lower than the fire spread due to the much wider mix of goods stored in ambient areas of a warehouse, though I accept that the sprinkler guidance does not generally recognise a like for like goods differential. There is the inevitable packaging which will potentially promote rapid spread across the surface but it is difficult to imagine deep penetration of meat, fish, vegetables and dairy products- you only have to look at cooking times to know that frozen food takes much longer to reach safe edible temperatures than its chilled counterpart.
My belief is that most serious freezer fires have been linked to inappropriate insulation matoerials and a lack of care during hot work. With LPCB approved panels universally used since around 2000 this risk has dininished somewhat. Always recognising that in such structures access and ventialtion are always going to be difficult firefighters will always have to make difficult decisions in respect of tactical mode.
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Fishy I would argue through instinct only that the fire loading relating to the contents in a freezer at -22C is likely to be lower than the fire spread due to the much wider mix of goods stored in ambient areas of a warehouse, though I accept that the sprinkler guidance does not generally recognise a like for like goods differential. There is the inevitable packaging which will potentially promote rapid spread across the surface but it is difficult to imagine deep penetration of meat, fish, vegetables and dairy products- you only have to look at cooking times to know that frozen food takes much longer to reach safe edible temperatures than its chilled counterpart.
My belief is that most serious freezer fires have been linked to inappropriate insulation matoerials and a lack of care during hot work. With LPCB approved panels universally used since around 2000 this risk has dininished somewhat. Always recognising that in such structures access and ventialtion are always going to be difficult firefighters will always have to make difficult decisions in respect of tactical mode.
I would agree with you entirely on all your technical points - initiation of a fire may be less likely. As regards the panels this wasn't recent - it when all the fuss about structural polymer core panels was kicking off (sometime shortly after the Sun Valley fire, if I recall correctly).
I'm not exaggerating, though - they seriously claimed that you would never get a fire because everything was kept below zero - my point was how this revealed some very muddled thinking!
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I'm not exaggerating, though - they seriously claimed that you would never get a fire because everything was kept below zero - my point was how this revealed some very muddled thinking!
Yes, I've found the same. I think some people think you can't strike a match in -22 degrees C!
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Yes, I've found the same. I think some people think you can't strike a match in -22 degrees C!
If only that was the case, as we would scrap our expensive (to run) hypoxic fire prevention system if we could replace it with a cold store :)
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The problem is the difference between the general temperature of the area and the local temperature at the ignition point. Hence in a freezer the general temperature may be -22 however the temperature of the flame (of the match) will be a great deal higher. falme will raise the temperature of the materials around it to above their flame point and away we go.
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As an electrical contractor many moons ago, we erected installations for refrigeration plant in a number of large cold stores. I remember one incident where the ammonia plant had been disconnected by the detection system and the manager was most agitated as he had just taken delivery of ?100K worth of a well known ice cream brand.
For me as a contractor a fire originating within the cold store would have been somewhat counter intuitive but the areas above and between are a different story. Our installations were always neatly erected but existing installations often comprised over worked plant, often shoved in to what was only suitable as a crawl space, wiring that was often thrown in and discarded materials and other rubbish that was strewn across the area such that it resembled a municipal dump on a windy day. I have no idea who did the structural calculations as some considerable weight from various plant would have been bearing down on the top of the insulated panels that acted as a ceiling for the cold room below. It is not hard to understand how a fire in the proximity of a cold room could cause the collapse of burning panels into the room and involve the contents, ice cream or whatever, in fairly short measure.
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I can relate to all of your observations Lyle. I believe things have moved forward since the year 2000, the Building Regs ADB contains guidance on the safe fixing and appropriate use of sandwich panels, inevitably if exposed to a fire they used to delaminate and lose all structural strength creating huge hazards for firefighting. The industry has also moved on with codes of practice and LPCB approved panels are used almost universally. delamination and collapse are less likely as a result, though fortunately my main former client tended to mount the plant on structural mezzanines above the freezer ceilings. Current practice is to make the building outer envelope the insulated lining and eliminate voids around and above the freezer box. Freezer plant is in an adjoining plant room and where CO2 is used tends to be much more compact than ammonia.
Before retirement it appeared to me that there was a move away from ammonia to CO2 but I am not sure how universal this is.
One concept I have struggled with is the pressure from some insurance companies to install sprinklers in freezers. We always have to recognise that due to a need for insulation doors are few and ventilation very unusual, creating potential hazards for firefighters. However where sprinklers are installed, and as storage tends to be on palletised racks, in rack sprinklers are often the only way of compliance with the codes. Obviously the system has dry pipes and in a fire will no doubt work as intended. But accidents do occur, one of my clients staff knocked off a head discharging water into the freezer, in the absence of heat from a fire plume it snowed for a considerable time creating havoc. The reinstatement was the hardest and most disruptive problem with all pipes in the vicinity having to be dismantled as it could not be confirmed that they were free of ice internally, moving frozen stock covered in ice was very difficult, expensive, dangerous and time consuming.
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I am glad to hear of the improvements Kurnal. I still provide technical help to one large facility and I can tell you that things there are as bad as ever!
I had a look at the NFPA data for multi million dollar fires in cold rooms in the States. Never ceases to amaze me how fires start! A lorry left its tail lights on as it rested against the buffer seal in the delivery dock to a large cold store. The seal went on fire, spread to polystyrene packaging and then into the insulation fabric. Despite attempts by employees to extinguish the fire, it was soon out of control. The facility had both wet and dry pipe sprinkler systems but that didn't stop its complete destruction at a cost of 28million dollars!
I noted also in some other instances that the sprinkler system had collapsed at an early stage, some failed, some were poorly designed and one had insufficient water reserves. Strange how insurance companies have to fork out millions to find these things out!
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Don't forget cold stores will now be using LPG as a refrigerant. Probably Propane (R290), Butane (R600), or Iso-butane (R600a).
http://www.fire.org.nz/Media/News/2008/Pages/Tamahere-Icepak-Coolstore-report-released.html
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Interesting report on a tragic incident with many learning points Sam. The freezer was very small compared to many, at 4000 sq m. There were many other issues with the site - to quote from the report:
"The Fire Service could also have identified the facility through its own processes, even though the facility lay outside the Hamilton Fire District. Ideally fire crews of the Hamilton district should have visited the facility as part of their own risk planning process, but for a number of reasons, including possibly the site?s location outside the district, this did not happen. The facility itself was always at risk from fire, with very large quantities of combustible material contained in the expanded polystyrene construction panels and also in the foodstuffs stored. There were no compliant fire detection or protection systems or hydrants, and very limited firefighting water."
I am interested to know whether the use of LPG for large scale installations has taken off. The report itself states that at the time if the incident there was only one other similar installation in the whole of NZ - I have not encountered such systems in my limited experience in the UK. To me it seems a no brainer- why would you install a system based on large scale explosive gases needing off site plans and DSEAR compliance etc when CO2 can do it relatively safely? Typical grocery retailers freezers in the UK are much larger than the NZ facility - typically around 20000m2 plus. I wonder if LPG installations are practicable on this scale? Interested to hear from anyone who has knowledge in this area.
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Pre planning is everything. We visited a huge cold store when I was in my water squirting days. As we were leaving, we became aware of a huge block of ice over the main forklift doorway.
The entrance had a rapidly lifting shutter to allow forklift trucks in and out but keep the cold in. In humid weather, the moist warm air entering the cold store would rise to the ceiling and immediately freeze. The cold store maintenance crews would chip away at the block on close down on Sunday evenings and estimated it could weigh about 2 tonnes
We noted that this may be the area where crews would be positioned when carrying out a defensive attack - ie in the doorway, so added it to a premises specific risk register. 2 years later, we had an 8 pump fire there on a Saturday evening and witnessed (from a distance) the entire block crashing to the ground.
Only pre-planning prevented serious injury or worse that evening
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I am interested to know whether the use of LPG for large scale installations has taken off. The report itself states that at the time if the incident there was only one other similar installation in the whole of NZ - I have not encountered such systems in my limited experience in the UK. To me it seems a no brainer- why would you install a system based on large scale explosive gases needing off site plans and DSEAR compliance etc when CO2 can do it relatively safely? Typical grocery retailers freezers in the UK are much larger than the NZ facility - typically around 20000m2 plus. I wonder if LPG installations are practicable on this scale? Interested to hear from anyone who has knowledge in this area.
Agree with you from a fire safety point of view, but do bear in mind that use of CO2 in large quantities is potentially extremely hazardous, given its toxic potential and the difficulty in dispersing it after any discharge or leak.
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given its toxic potential
Sorry to be pedantic CO2 is not toxic it's an asphyxiate and plays havoc with your medulla oblongata and bring back the proto sets. ;)
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given its toxic potential
Sorry to be pedantic CO2 is not toxic it's an asphyxiate and plays havoc with your medulla oblongata and bring back the proto sets. ;)
Forgive me, but I do beg to differ re: toxicity...
http://www.hse.gov.uk/carboncapture/assets/docs/major-hazard-potential-carbon-dioxide.pdf
http://www.nist.gov/el/fire_research/upload/R0000286.pdf
I would never enter a large area with a CO2 extinguishing system in it - locked off or not!
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Fishy I am not saying it is not a major hazard I am saying it is not Toxic and I cannot find anything in those article that says different.
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Sorry Tom, after haveing a look at the articles I agree with Fishy, it is toxic. In high concentrations it will suffocate you but in lower concentrations it will mess with your blood chemistry and kill you.
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yup CO2 is toxic, but you have to try pretty hard to get poisoned by it.
CO of course will kill you in a blink.
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Need to get those toxic labels on CO2 extinguishers!
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To me its down to lesser evils. Main choices are:
Ammonia - if things go wrong theres a possible big bang and toxicity to contend with, toxicity and explosion alarms required
LPG - If things go wrong theres an inevitable very big bang and possible gas clouds before a big bang, if its still contained theres a risk of bleve Major controls and explosive alarms needed
CO2 serious risk of asphyxiation no risk of fire or explosion, asphyxiation alarms needed.
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Sorry Tom, after haveing a look at the articles I agree with Fishy, it is toxic. In high concentrations it will suffocate you but in lower concentrations it will mess with your blood chemistry and kill you.
Extract from HSE documentation:
"CO2 has been shown to exhibit a level of toxicity related to the concentration and time of exposure...
...CO2 is commonly thought of as posing a threat to life through asphyxiation when it displaces the oxygen in air down to dangerously low levels. For CO2 to reduce the oxygen concentration in air down to a level that is immediately dangerous to life, the CO2 concentration would need to be in the order of 50% v/v. Evidence shows, however, that CO2 does create an immediate threat to life at a concentration of only 15% in air due to the toxicological impact it has on the body when inhaled at this concentration".
I do stand by my comments about CO2 at the concentrations used for fixed fire extinguishing systems - which are typically far in excess of those mentioned as being hazardous in the above documents (your typical portable fire extinguishers are a different matter entirely) - my take from the literature is that a few breaths at anything above 25% will be enough for quite a good proportion of us to be rendered unconscious within seconds. No asphyxiation alarm will help if it takes you a long time to get out of the location, unless you've got immediate access to emergency BA. As I said, I would never enter one of these locations unless a) it was so small that I was absolutely sure that I'd be able to get out within seconds and b) someone competent assured me that there had been no release of CO2 in that location. That's an entirely personal choice - not suggesting that others ought to have the same opinion!
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I stand corrected and this should mean quite a few document needs amending as well as considering the colour coding of cylinders.
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Tam, people used to be taught 100 years ago that it is not toxic, but it was always wrong; as I recall it attacks the CNS. It is easy to prove just by common sense. If it was purely an asphyxiant, it would kill you at the same concentration as an inert gas, which is certainly not the case.
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If the cylinder is red it will burn you, if it is yellow it will poison you. If it's both you need an a hazmat officer.
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Tam, people used to be taught 100 years ago that it is not toxic, but it was always wrong; as I recall it attacks the CNS. It is easy to prove just by common sense. If it was purely an asphyxiant, it would kill you at the same concentration as an inert gas, which is certainly not the case.
Colin in my case it was about 60 years ago but I am pleased I tried to make a point and was decimated which made me get down to some research.
There is much conflicting information, out there, but now would treat CO2 with far more respect. At high levels, the initial symptoms up to unconsciousness, is very quick (at 30% 26/27 secs) and would agree with fishy, BA a necessity but I also fully agree with Kurnal, if I had to deal with a cold store incident then I would certainly prefer the refrigerant to be CO2.
He never mentioned the ammonia burns to the nether regions it was like Vinnie Jones grabbing you with superhuman strength.
As you said the CNS is involved, blood pH is tightly regulated by a system of buffers that continuously maintain it in a normal range of 7.35 to 7.45 (slightly alkaline). Blood pH drop below 7 can lead to a coma and even death due to severe acidosis. This causes depression of the central nervous system.
High blood pH (above 7.45) is called alkalosis. Severe alkalosis (when blood pH is more than eight) can also lead to death. Respiration and the renal organs are two of the buffers and if the lungs are not removing the CO2 from the blood, because of excess CO2 in the lungs, then the ph value will drop. (Brown Bread)
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/464950/Carbon_dioxide_IM_PHE_300915.pdf