Scotchmist

Water that thinks it's a Gas

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BRE Prison Cell Test Protocol

With more than a thousand fires a year, prisons in England and Wales need very specific means to suppress fires and allow the safe but secure evacuation of cells.

Tests conducted
BRE Global conducted a series of 29 fire tests in a test ‘cell’ measuring 3m x 4m x 3m high, including:

  • A ‘baseline’ fire scenario with no suppression system (this fire scenario was then subsequently used for further tests)
  • A cell ‘burnout’ test with a high fuel loading to assess the potential fire size and heat release (with the cell door left open)
  • Eight ‘feasibility tests’ on identified ‘tool kit’ options
  • 19 tests with industry provided commercial systems (12 different system providers).

Findings
The cell ‘burnout’ test (left) with a high fuel loading and open cell door resulted in a severe and large fire (see graph, right). Heat release rate measurements indicated a peak heat release in excess of 2.5 MW. As can be seen in the graph for heat release measurement from the cell fuel loading test (see graph, below), the heat release rate may not have peaked at the time that the fire was manually extinguished.

The BRE Global developed fire scenario was burnt in the test room with no suppression system operation. Highly hazardous conditions resulted for both cell occupants and staff rescuers and conditions became life threatening after approximately 10 minutes.

All the suppression systems tested improved room tenability (asphyxia and heat conditions) compared with the unsuppressed fire. All but one of the systems submitted maintained survivable conditions in the test room for a period of 20 minutes, and tenable conditions for staff rescuers for a 31/2 minute period.

Of particular interest were a number of tests where it was noted, subsequent to the actual test from cold water discharge testing, that there was very little water reaching the fire location. In these tests the fire began to increase in size (see graph, left) but was then suddenly suppressed or extinguished a few minutes later (whilst oxygen levels were still reasonably high and capable of sustaining combustion). This was likely to have been due to the steam produced by a larger fire and room humidity conditions not supporting flaming combustion. These test results indicate that it is difficult for fires to increase above a certain size in the presence of water mist in limited volume cells with limited ventilation.

The programme of work conducted was an unparalleled detailed assessment of a diverse range of internationally provided water mist fire suppression systems for a particular application. The work has been of interest internationally and it may be possible for many of the findings to be extrapolated to prison environments in other countries. The project has provided the Ministry of Justice with a clear evidence base and accompanying documentation for appropriate specification and installation of water mist systems for prisons.

End of Extracts from the BRE Report.

Scotchmist Specifics

Scotchmist was one of the mist systems successfully tested and the image on the left shows a 'wet' run, with mist filling the test cell.  On the right can be seen the test fire load, consisting of bedding and the paraphernalia of everyday living.

 

 

A close comparison of the pre-burn fire load (left) with the post-burn load (right) shows how much of the material remains intact following extinguishment by Scotchmist.

 

 

A test engineer opens the test cell door during the suppression period (left) and as the post combustion fumes are extracted, it's clear that the fire has been extinguished (right).   

Test Protocols