Case Notes (Edited by F. L. Cann)

A NOVEL GUY FAWKES BOMB

On the night of 4 November there was a loud explosion like a bomb at street level in the vestibule of a small apartment building. The blast burst open the door to one of two flats on the first floor at the head of a single flight of stairs and resulted in a complaint to the Police of property damage. I t was found to be a prank involving the explosion of a rubber balloon filled with a mixture of acetylene and oxygen.

When the Police investigated the scene, they found no residues of explosive nor fragments of fuse or detonator. There was, however, a considerable quantity of shredded newspaper, some charred. In the debris were fragments of a blue rubber balloon including the neck which had been closed with a thumb knot. Closer examination also revealed minute fragments of paper and of rubber balloon adhering to the walls and ceiling of the vestibule and stairway. This debris indicated that the centre of the explosion was almost certainly in the middle of the bottom step of the stairway at the back of the vestibule. In this area was a patch of brown staining, possibly from something having been burned there.

The damage caused by the blast consisted of : 1. The burst open door on the landing. The blast had forced the bolt keeper

off the back of the doorway by tearing the retaining screws out of the woodwork.

2 . The Gibraltar board ceiling had been split with a large star pattern crack above the landing, and had been sprung for most of its area so that some ceiling nails protruded about one half inch in several places.

3. The frame of the window 6 feet high by 1 foot 9 inches wide above the vestibule had been moved out about one half inch at its base.

Following Police enquiries a youth admitted the following prank. As a panelbeater he had access to an oxy-acetylene torch and had filled a balloon with the mixture of acetylene and oxygen. The balloon was closed with a thmub knot and then wrapped in newspaper. To explode the device the youth merely set fire to the newspaper.

His explanation is consistent with the shredded newspaper, some charred, the balloon fragments, the balloon neck closed with a thumb knot, the possible charring on the bottom step and the absence of residue of explosive, fuse or detonator.

When the youth filled the balloon, the oxygen gauge was set at 351bs. and the acetylene gauge at 15-201bs. Although the relative resistance of the jets is not known it seems likely that the mixture would have contained about 30% of acetylene. Balloons purchased at a chain store were found to contain up to 0.35 cubic feet when blown up hard.

According to Sax (Handbook of Dangerous Materials, 1951, New York), the explosive limits of acetylene in air are 2$ per cent to 80 per cent, this being one of the widest explosive ranges known. These acetylene-air mixture limits are equivalent to acetylene-oxygen mixtures containing from 10 per cent to 95 per cent acetylene.

The charge of Arson (Damaging Property by Means of an Explosive) was later reduced in the Magistrates Court to one of Wilful Damage. The offender was convicted and fined £5 and ordered to pay restitution.

This bomb incident is reported because : (a) A bomb of this type is readily prepared but leaves no residue of explosive

or detonator. (b) There was a surprising amount of damage from so modest a device. Chemistry Division, D. F . Nelson Defiartment of Scientific and Industrial Research, Auckland. N e w Zealand.

SMOKE DAMAGE TO TEXTILES

Whenever there is a fire on premises where textile material has been on stock (whether as piece goods or as garments), the assessor for the textile firm alleges "smoke damage", and the adjustor for the insurance denies such damage, unless there is easily visible soiling of the cloth.

If there is no visible soiling, the textile firm is worried about the possibility of "smoky smell" developing. I t is quite obvious that if a warehouse has been full of thick smoke, some of this must have become deposited on the cloth. If the warehouse has been "cleared" by means of an aerosol, the latter may consist of an odourless hydrocarbon containing a trace of deodorant perfume. The fine droplets collect any particulate matter, and the theory is that these droplets are removed together with the "smoke" when the warehouse is vigorously extracted by fans subsequent to the aerosol treatment. This procedure, however, has no effect upon smoke previously deposited upon the cloth.

Traces of particulate matter which are not visible by ordinary examination can be ignored as unimportant. However, when organic matter burns, various non-particulate pyrolytic breakdown products are released, liquid in character, and if these become adherent to the cloth, their odour can become apparent when garments made from the cloth are worn under certain conditions, e.g. a combination of warmth and humidity.

In the past, it has usually been equally difficult for the assessor to prove that the risk exists, or for the adjustor to prove that there is no risk.

In a recent case of this kind, an attempt was made to prove the presence of pyrolytic decomposition products, by a technique involving thin-layer chroma- tography. Fortunately, a roll of cloth had been cut into suit-lengths, which were distributed amongst a number of branches, so that precisely the same cloth quality was available from (a) the premises where the fire occurred, and (b) premises where no fire had occurred.

Samples of the smoke-exposed cloth were extracted with methylene chloride. The extracts were evaporated to a small volume, and developed on silica-gel prepared chromatographic plates, using as elutrients (1) methylene chloride and (2) methanol-i.e. one solvent from the middle, and one from the polar end of the Brockman series.

Samples of the unexposed cloth were similarly treated. Aldehydes and phenols were identified on the smoke-contaminated samples

by spraying the plates with (a) malachite green which had been decolorised with sulphite and (b) ferric chloride/hydrochloric acid. Similar spraying of the plates from the original cloth, yielded no result.

The spraying reagents used were : (a) malachite green-dissolve 1.6 g in 12 ml water, bring into solution by adding 6g sodium sulphite and warming. Add a further 4g sodium sulphite, and filter. (b) ferric chloride/hydrochloric acid-mix 10 ml 0.5 per cent ferric chloride with 50 ml conc.HC1.

I wish to thank Mr. W. Gamer for suggesting this procedure. J. Murphy

London Textile Test ing House Ltd., Alderton Lane, Wembley, Middlesex, England.