Fire Safety Journal 17 (1991) 85-93

Major Fire Disasters Involving Flashover

D. J. Rasbash

3 Wilton Road, Edinburgh EH16 5NX, UK

ABSTRACT

Three major fire disasters are considered: Summerland, Isle of Man, 1973; Stardust, Dublin, 1981; King's Cross Underground Station, London, 1987. In all three cases many fatalities were caused by a sudden extensive development of fire followi,lg a period in which the fire was much smaller. Evidence indicates that the occurrence of a local fire capable of exposing a part of an extensive combustible surface to a high heat transfer rate was a major factor. In all three, lapses in Fire Safety Management contributed to the presence o)some of the extensive combustible surfaces involved.

INTRODUCTION

The author has been concerned in different capacities with investiga- tions into three major fire disasters: the Summeda~d Leisure Centre, Isle of Man, ~ the Stardust Disco fire, Artane, Dubli'~, 2'3 and the King's Cross Underground fire, London? These fires werp all associated with the sudde~l eruption of a large volume of flame, ~rhich was the major cause of the many deaths that occurred. Although the term flashover was used in each case, the nature of the phenomenon was different in kind from ~he flashover in small rooms that has been studied exten- sively ii~ the past. However, the three fires had much in common.

85 Fire Safety Journal 0379-7112/91/$03.50 © 1991 Elsevier Science Publishers Ltd, England. Printed in Northern Ireland

86 D. Y. Rasbash

THE SUMMERLAND FIRE, ISLE OF MAN

As a Crown witness, the author was expected to give a view of the fire dynamics of the Summerland fire (Fig. 1). The very rapid spread of fire in this instance took place within the amusement arcade, 32 m long by 17 m wide and 4.5 m high, which formed one of the lower spaces in the open leisure complex (Fig. 2). The fire then spread to the Oroglass (poly(methyl methacrylate)) walls and roof, which also became in- volved very rapidly, and to other spaces in the complex. The fire had been developing unseen for about 20 min in a 0.3 m wide cavity (Fig. 2), which formed a part of one side of this arcade. The crucial common wall between the cavity and the arcade was of decalin, a form of fibre board (class 4 in the BS 476: part 7--spread of flame testS). The opposite face of the c~+vity, which was also the outside wall of th+~ building, was sheet steel, surfaced on both sides with 300 g/m 2 of resin. This material had passed a roof test where it had been exposed to c. 10 kW/m2. However, it was ignited at X when a plastic booth outside was set on fire by children. It was estimated that the heat transfer from the burning booth to the side of the building would have been about 60 kW/m 2.

Within the confines of this cavity, to which air had limited access, a

Fig. 1. General view of Summerland Leisure Complex.

Major.fire disasters involving ]tashover 87

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fuel rich fire developed. Then the fibre board wall burned through, a large volume of fuel rich gases was ejected into the arcade, fofiowed by continuous flame from inside the cavity. This could have acted as a powerful ignition source for the combustible wall surfaces that were present in the arcade. Although no estimate was made of the heat transfer at the time, the emerging flame could well have been over 1 m thick and capable of transferring 100 k W / m 2 to neighbouring surfaces. The flame spread along the arcade within tens of seconds and flowed upwards over its open end to affect upper stories. However, it was difficult to account for the amount of flame that poured out of the arcade, even assuming that all combustible surfaces known to be present and sensitive to rapid involveme, nt had indeed become fully involved. In hindsight this may have been due to the burning of gloss paint which may have been present on sprayed asbestos under the ceiling. This was not checked at the time.

THE STARDUST CLUB FIRE, DUBLIN

The author was an assessor for the inquiry into the Dublin disco fire. Up to flashover, the fire involved an alcove (A, Fig. 3), measuring 17 m by 10 m, with a floor which sloped upwards towards the back where the height was 2.4m (Fig. 4). The alcove, which was initially empty and partially cut off from the main body of the dance hall by a roller blind,

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had rows of seats each measuring 0.9 m long with 5 cm thick PVC covered polyurethane foam seating and backrests. The back row was installed against the back wall which was lined with carpet tiles (Y); these gave class 3 to 4 performance in the spread of flame test. Mineral fibre insulating tiles, which were almost noncombustible, formed the ceiling (C) of the alcove above which there was a roof space (R). Some mechanism caused ignition on the back row of seats at Z so that a line fire developed. The people in the hall were aware of there being a small fire in this area for some 6 to 7 rain, during which time the roller blind was raised. The flame impinged on the carpet tiles and the back wall rapidly became involved. Then, within tens of seconds, all the seats in the alcove began to burn, and flames and smoke spread very quickly to the main body of the ballroom.

Experiments at the Fire Research Stat ion e(p'4~6,p's46) showed that when one of the 0.9 m seats was ignited along its whole length it could produce a heat transfer rate of 100 kW/m 2 on the back wall. The combination of burning seats plus carpet tiles produced a burning rate at the back of the alcove of about 800 kW/m run, sufficient to produce extensive flaming under the ceiling and high levels of radiation down on the seats in front. An unexpected measurement in full scale tests was that the heat transfer from the flames just ahead of the back wall rose rapidly to a peak of 250 kW/m 2 which, as far as the author is aware, is still the largest measured in a fire of this kind. The result was that the

90 D..l. Rasbash

tops of the seats well ahead of the back wall were exposed to a heat transfer in excess of 60kW/m ~, sufficient to produce spontaneous ignition in a few seconds. The array of seats below the ceiling acted as an extensive surface which could respond to the very high heat transfer rates.

A noteworthy point is that part of the ceiling in the alcove collapsed, which led to the shattering of the roof and the venting of much of the heat and smoke. Forty-eight young people died in this disaster, but had venting not occurred, it is likely that many more of the 800 people in the hall would have been killed.

THE KING'S CROSS UNDERGROUND STATION FIRE, LONDON

The King's Cross fire involved a wooden escalator about 40 m long leading to the booking hail. It was the left hand escalator of a group of three running at an angle of 30 ° in a semicircular shaft 8 m in diameter. The side balustrade and hand rail of this escalator was separated by a distance of 0.3 m of combustible horizontal surface from the wall and ceiling of the escalator shaft. Surfaces on the escalator were class 3 or 4 spread of flame, including the risers and treads of the steps, the balustrade and probably also the laminated surfaces separating es- calators from each other and wall. In addition, the first metre of the wall and ceiling was an advertising hoarding which, because of the presence of varnish and plastic covered advertisements, was the most flammable item associated with the escalator shaft. There was also evidence that the ceiling had been recently painted in such a way to cause it to have a likely class 3 or 4 performance in the spread of flame test. When a sample which included the plaster and concrete base was exposed to a heat transfer of 75 kW/m 2 in a cone calorimeter, a number of layers of the paint delaminated in 2 to 3 s, ignited in 5 s and produced a heat output of between 200 and 450 kW/m 2 and much smoke for about 20 s.

In this incident, whaC~appeared as a comparatively small fire in the middle of the escalator, suddenly shot up the escalator after a period of about 15 min and quickly involved the upper part of the escalator shaft as well as the combustible material in the booking hall above. People in the booking hall were confronted with a wall of flame and black smoke moving rapidly towards them.

The author was brought into this inquiry at a late stage, representing London Transport, as there was a difference of opinion between the

Major fire disasters involving flashover 91

inquiry Commission and themselves. The Inquiry Commission had been advised that the escalator had become involved to give a heat output of some 7 MW, and that was sufficient for the flames to spread upwards, and stretch under the ceiling to involve the top of the three escalators and the hall in the short period observed. London Transport believed that the fire could not have been this big when it took off and suggested that the paint under the ceiling had been a major factor in promoting the rapid fire spread.

However, a field modelling study carried out at Harweli, which was reported late in the investigation, indicated that flames within the trench of the escalator instead of moving up to the ceiling, as had been assumed up to that point and indeed had not been contradicted by the limited experiments with steps that had been carried out, were likely to have been confined to the trench itself for a significant time, thus promoting flame spread along the escalator. Tests on a one-third scale escalator plus shaft system, carried out by the Health and Safety Executive, showed that this could indeed have been the case. Heat transfer rates within the escalator trench of about 150 kW/m 2 were measured, and were found to be predominantly convective rather than radiant heat transfer. It was decided by the Inquiry that this was the mechanism of rapid fire spread.

However, it is the opinion of the author that spread of fire out of ~he trench on to the advertising hoarding, which was also observed, might have rapidly produced a line source heat transfer to the ceili~g of the order of 100 kW/m 2 and a consequent spread up the hoarding-ceiling combination and under the ceiling to the booking hall in about 20 s. There could thus have been a double blow awaiting those in the ticket hall.

OBSERVATIONS

The common factor in all three of the fires is the emergence of a flame capable of taking part in the spread process with a heat transfer capability of the order of 100 kW/m 2 towards an extensive area of surface which can very rapidly respond to this high rate of heal transfer. In standard fire spread tests, we are used to thinking of heat transfer rates'of a few tens of kW/mL Thus, 37 kW/m 2 is the maximum at the hot end in the Surface Spread of Flame Test, BS 476: part 7. s However, if the thermal inertia of the fuel, plus its backing, plays a substantial part in its resistance to ignition, one can expect a heat transfer of 100 kW/m 2 will be 25 times faster in igniting the material than a heat transfer of 20kW/mL Also, the concurrent flow of flames over the

92 D. J. Rasbash

surface if it occurs, rather than the opposed flow which is the norm of spread of flame tests, would accentuate the difference still further. In each of the case studies, the mechanism of flashover was different from the classical model associated with flashover in a small room in that, in the latter model smoke and hot gases build up under the ceiling to irradiate downwards on to combustible surfaces at about 20 kW/m 2.

There were some other interesting common factors with these three disasters. At least one of the crucial extensive combustible surfaces in each case was introduced inadvertently in the face of different initial design concepts. The decalin fibre board at Summerland was intended initially to be a plaster board. It is thought that it was changed to decalin board because the sound absorbing properties were better. The carpet tile wall at the Dublin fire was intended to be left as plain concrete, but was changed because carpet tiles were so much nicer for the clients. The paint on the ceiling at King's Cross should have been put on after thick layers of old paint present had been removed. The newly painted surface would probably then have been class 0 to 1, instead of class 3 to 4 and less responsive to high rates of heat transfer. The fact that the floor of the escalator itself, because of its 30 ° slope, would approach the flame spread performance of a vertical wooden wall was quite unsuspected and not observed in rather numerous fires on escalators which had taken place previously.

In all three cases there was a significant period, of several minutes at least, in which the fire was small, during which an orderly evacuation process could have been put in hand. However, in none of the cases were there significant evacuation procedures laid down nor did staff receive any relevant training. Indeed, there was a tendency Jn all three cases for people to stay and look at the fire or just to ignore its presence.

CONCLUSIONS

The disasters point to four major lessons for Fire Safety Engineers:

(I) Awareness that under some conditions local fires in buildings can produce high rates of heat transfer of the order of 100 kW/m 2.

(2) The possibility that extensive surfaces might respond very rapidly to these high heat transfer rates to produce rates of flame spread over a large area, which might approach I m/s.

Major fire disasters involving flashover 93

(3) The necessity to see that during design erection and main- tenance of buildings, conditions that might give rise to factor (1) or (2)--particularly (2)---are not brought in unawares.

(4) To have a properly designed and managed emergency evacua- tion procedure continually in place while premises are occupied.

If we are to produce systems models aimed at avoiding fire disasters, account will need to be taken of all the above factors. It would also be desirable to set up a databank of what might give rise to factors (1) and (2).

REFERENCES

1. Report of the Summerland Fire Commission, Government Office, Isle of Man, May 1974.

2. Report of the Tribunal of Inquiry on the Fire at the Stardust, Artane, Dublin. Stationery Office, Dublin, June 1982.

3. Pigott, P. T., Fire Safety J., 7 (1984) 207-12. 4. Investigation into the King's Cross Underground Fire. Her Majesty's

Stationery Office, London, Nov. 1988; Fire Safety ,/., (in press). 5. BS 476. Fire Tests on Building Materials and Structures, part 7. Methods

for Classification of the Surface Spread of Products, 1987.