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PM Engineer, 4, November 9, p. 42, 45, 1998-11-01
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Fire protection: Canadian research boosts water mist as halon
alternative
Liu, Z. G.
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Fire prot e c t ion: Ca na dia n re se a rc h boost s w a t e r m ist a s ha lon
a lt e rna t ive
N R C C - 4 1 3 2 2
L i u , Z . G .
N o v e m b e r 1 9 9 8
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PM Engineer, 4, (9), November, pp. 42, 45, November 01, 1998
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FIRE PROTECTION:
CANADIAN RESEARCH
BOOSTS WA.TER MIST
AS
HALON ALTERNATIVE
ecent research at Canada's Institute for Research in Construction (lRC) will have implications for the use of water-mist systems as a replacement for halonincertain circumstances.
Following the ban on halon production by the Montreal Protocol, IRC's Fire Risk Management Pro-gram, in partnership with the Department of National De-fence (DND), has been looking for alternative fire-suppression systems to use -as replacements for existing
42.-PM::NGINEER,November 1998
by Zhigang Lill, Ph.D.
i
equipment and in future designs. It is of primary impor-tancethat the use of such systems does not compromise the firefighting effectiveness currently provided by halon, have negative implications for the environment nor create unacceptable safety risks.
Water-mist fire-suppression systems have good potential to satisfy all of the above criteria. Recently, IRC carried out full-scale tests to study the feasibility of using water mist as an alternative to halon in DND Halifax Class Frigates, and to compare the fire-extinguishing performance of water-mist systems to that of gaseous agents evalu-ated previously.
As part of the tests, a mock-up of a diesel engine casing was installed in the test compartment. The 'researchers chose fire scenarios-including
differ-ent sizes, types and locations of fires-that presdiffer-ent- present-ed the greatest challenge for water mist to extinguish. Ventilation conditions varied from closed door to open door (natural ventilation sys-tem) to open door combined with an operating･ｸｾ haust fan (forced ventilation system). Two types of water-mist systems were usedinthe tests: 1) a sin-gle-fluid/high-pressure system and' 2) a twin· fluid/low-pressure system. In addition, the effects of two water-mist discharge modes, continuous and cycling discharges, were examined.
The test results showed that the thue required for extinguishing fires when water-mist systems were used ,was longer than when gaseous agents were used. However, water mist quickly controlled fires and significantly cooled the test compartment, hence keeping combustion products (CO and CO2) in the compartment at a low level. The ther-mal conditions and gas concentrationsinthe com-partment, after the water-mist application, were safe enough for firefighters to enter the compart-ment immediately.
Safe levels of CO, C02
The measurements from the tests showed that water mist did not produce thermal decomposition products as a result of the breakdown of
halocar-,
WATER MIST
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ing analysis carried out by IRC provid-ed new insights into water-mist SYSM terns as an alternative to Halon 130I. .
In addition, some possible approach· es for further improvement of waterM mist fireMsuppression performance were identified. PM;:
Reprinted with permission by Con-struction Innovation, a quarterly
publication Of the Canadian National Re-search Council's (NRC) Institute for Research in Construction. Dr. Zhigang Liu is a research associate at the NRC
specializ-ing in research on halon alternaM
tives and ｷ｡ｴ･ｲｾｭｩｳｴ fire
suppression. He received his Ph.D. in mechanical engineering from the University of Calgary. He may be reached at 990-5075, fax 613-954-0483 or bye-mail at zhigang.liu
@nrc.ca.
Water-mist
systems were
able to extinguish a wide
variety ojJires under
ventilated conditions
bon agents during fire suppression. In all tests, the CO and CO2
concentra-tions in the test compartment were
not high enough to pose an immedi-ate danger to life and health.
The results also showed that water· mist systems were able to extinguish a wide variety. of fires under ventilatｾ
cd conditions, while the gaseous
- agents were not effective 'in ･ｸｾ tinguishing fires under these con-diti()fi:5' Ventila-tion in the compartment re-duced the CO and CO2 con-centrations in the room, but
prolonged the time required to extin-guish the fire because of the addition-al oxygen supply.
One of the significant findings from the tests was that the performance of the water-mist system, in terms of ex-tinguishing the fire, could be substan-tially improved by using the cycling
discharge mode rather than the con- , _
tinuous discharge mode. When the
type of fire was one where water mist
could easily extinguish it, the
im-provement achieved by using the cy-cling discharge was not significant. However, even for these conditions, it was possible to reduce the amount of water required to extinguish the fIre by using the cycling discharge.
For fires that are more difficult to extinguish with water mist-for eXM ample, small fires, shielded fires and fires in ventilated conditions-both the time required to extinguish the fire and the amount of water required were substantially reduced when the cycling discharge was used. The test results showed that the water requireM ment was oneMthird, and the time to extinguish the fire was one-half that of the continuous discharge. The cy-clingｷ｡ｴ･ｲｾｭｩｳｴ 'discharge also extinM guished fires that the continuous discharge could not.
The test results also showed that unlike other fireMsuppression agents, the waterMmist discharge created strong dynamics that mixed combus-tion products with steam in the com· partment, which played an important role in putting out the fIre andreduc· ing the impact of air convection on extinguishing fires.
The fullMscale tests and correspondM I
