Carbon monoxide - L1?

[Paul2886]

It was always my understanding that CO is produced by incomplete combustion. (ie, an oxygen starved fire). With a well ventilated fire is it not CO2 that is produced. So is there a possibilty in a sleeping risk of smoke production with no CO of any significance.

[bungle]

I seem to remember that BS 5839 makes a specific reference to CO detection not being suitable for fires involving some flammable liquids as the combustion is so "clean" and so will not actuate.

Bungle G I Fire E

[CivvyFSO]

Yes, Brian, they almost certainly will. And if they aren't they shouldnt have mugged the old age pensioner in the first place.

Class. 

When working out cost/benefit etc I think you can assume that a death of a normal law-abiding citizen costs society over £1 million, so would the death of someone being kept at societies expense even show up? Cost of detector head... £30. Cost of not having the detector and the person dying in-situ... A saving of over £30,000 a year. It would all depend on the sentence: If you have a 35 year sentence you clearly do not warrant anything as expensive as a detector.

[afterburner]

Wee Brian
yes the prisoner is most certainly alive when the CO detector activates, because fires in cells do not burn efficiently and cleanly. It is a very small cubic space with a very limited air supply to feed the fire (locked doors and limited opening windows), so the fires seldom (very seldom) burn cleanly nor efficiently. Immediately outside the cells the space is protected by optical smoke detectors

As an additional detail, our new build project cell blocks have high pressure water mist systems operating off a 57 Degs. C frangible bulb, which we also classify as a 'life safety' head detection system (alarm generated from flow switch immedaitely behind the operating head).

If you are interested in this application of fire detection systems please contact me directly.

[colin todd]

Afterburner. Extremely well explained, as you would expect from a man from Edinburgh. Your explanation is also the answer to Paul's question. In sleeping risks, the fire will often be ventilation controlled, and will soon burn inefficiently, so producing CO. With regard to clean burning fires from alcohol, the BS points out they wont be detected by smoke detectors, as there is no smoke. You can show that a beam detector with a thermal turbulence facility picks up an a raging alcohol fire by thermal turbulence rather than obscuration. Equally, that is all very academic unless you envisage an alcohol fire with no other combustibles involved.

[Paul2886]

Sorry Colin I cannot accept your theory about the fire soon burning inefficiently therefore producing CO. For a fire to burn inefficiently in a room it needs to start exhausting the oxygen supply first. It will be an established fire that draws on the oxygen within any room before signifant CO is produced. Therefore many types of fire will produce significant levels of harmful smoke that would, and could go undetected if no smoke detection is fitted.

[kurnal]

I would question whether a fire in a cell would be ventilation controlled but clearly my experience is very limited as I have no  direct experience of prison or custody cells, whereas a number of you appear to be well acquainted with them?

I understand there to be very tight controls over combustible materials, with very few furnishings are a retardant thin mattress and bedding  bedding and the clothes the prisoner stands up in? And are there not ventilation ducts drawing the foul air out and bringing in fresh air from outside? Or is it not like that outside Alcatraz?

[wee brian]

Nah, prison cells have more fire load than you can shake a stick at.

TVs, Playstations books videos etc etc.

And some very unstable people.

They get fires all the time so afterburner may be talking from experience. I expect the've tested the watermist too. Perhaps he could enlighten us....

[afterburner]

Wee Brian, as requested a response about prison cells. (and I'll try to give as much information as I can within the sensitivity of this discussion)

You are absolutely right about the fire load. The cells are provided with fire retardant mattresses and bedding (although some of the bedding can be outwith the standards). The huge fire load components come from the Prisoner's possessions, which include clothing, electrical items, and paper in the form of books and magazines. However quantities of free burning accelerants is severly limited through routine checks.

We have a tiny number of fires outside cells. We have a fair number in cells. Only a very limited number of these in-cell fires have an 'accidental cause'

Our watermist system was fully tested by a third party fire engineering company, by building a portion of a cell wing in a test facility, establishing a test fire load using 'real' materials which could be replicated for subsequent tests, and setting up a test recording process which would record temperatures, toxin levels (HCN, HCl & CO) at 9 points in the cell.

The test outcomes were measured against pre-determined tenability criteria to ensure that post ignition the fire did not cross a life threatening threshold within the cell before or after the watermist system operated. These tenability criteria included a maximum CO value (measured in parts / million) and a maximum teperature at head height (the prisoners head and not the watermist head) of 60 degs C.

The system passed the series of tests although the the CO generation did edge towards the criteria limits. The happy news is that post operation the temparture curves from all 9 sensors fell off almost vertically. Toxin recorders also showed a remarkable decline in the toxins due to the effect of the mist. 

It was these test which woke us up to the actual quantities of CO which are produced during a fire in a cell. so, where watermist is not installed we now use in cell systems such as CO detection, aspirating sytems (far too prone to induced false alarms) and optical detectors.

As for ventilation, there is a 3 mm gap all the way around the door and a window opening which is actually an air opening rather that the accpeted sense of an open window. Cells are not air conditioned, and the only ventialtion ducts available are foul air exchangers from the toilet facilities.   

[colin todd]

Paul, Read the research work on CO detection. It is too long to set out here. But, if there is a classic application for CO detection, it is bedrooms in sleeping risks. Thats why a number of hotels have CO in the bedrooms. You will also find that they pick up smouldering mattresses before an ICSD will.

[nearlythere]

Paul, Read the research work on CO detection. It is too long to set out here. But, if there is a classic application for CO detection, it is bedrooms in sleeping risks. Thats why a number of hotels have CO in the bedrooms. You will also find that they pick up smouldering mattresses before an ICSD will.

Is there a specific document you could point to?

[wee brian]

Afterburner - good stuff. Its good to see people doing their homework.

My only doubt about the watermist was the activation using a thermally sensitive bulb. I didnt think it would be quick enough.

[afterburner]

WB,
I agree, in most other 'ordinary' applications the frangible bulb may well be too slow. But in a cell, with only 14 cubic metres of space to heat up, and very solid walls which are far from being an efficient 'heat sink' the energy from the fire is very rapidly transmitted to the bulb. We realised that during this 'energy transmission' stage the ceiling tempertures would be slightly in excess of 100 degs C, which is where the tenability measure of not exceeding 60 degs at head height came from.

[kurnal]

Hi Afterburner - did you have any timelines you could share with us showing time to detection, time to reach your tenability parameters and the  operation of the water mist?

[afterburner]

Hi Kurnal

the shortest time from ignition to water mist activation was 90 seconds, the longest time was 160 seconds. (despite our best attempts to create a fire load which was exactly the same each time, naturally enough the fires did not behave exactly the same way every time).

On activation we had a established a 'response time' (theoretical time for an Officer to reach the cell and unlock the door long enough to let the occupant leave and then re-close the door). Each test had to pass the tenability criteria of a time line which was (a) ignition (b) activation (c) + response time and door release sequence.

Best results were ignition to completion in 150 seconds and worst case was 245 seconds. However overall the tenability criterai were never breached