GB2228044A

GB2228044A - Letterbox incorporating fire-extinguishing means

Info

Publication number: GB2228044A
Application number: GB8928220A
Authority: GB
Inventors: Graham Barrie Phelps
Original assignee: AUTOGUARD SECURITY SYSTEMS LIM
Current assignee: AUTOGUARD SECURITY SYSTEMS LIM
Priority date: 1988-12-13
Filing date: 1989-12-13
Publication date: 1990-08-15
Anticipated expiration: 2009-12-13
Also published as: GB2228044B; GB8928220D0; GB8829067D0

Abstract

A letterbox has two openings closable in a substantially gas tight way by flap means 12,40, the letterbox containing fire extinguishing means 50,51 that are automatically activated by sensing means when a fire takes place in the letterbox. <IMAGE>

Description

Fire Resistant Letterbox The present invention relates to letterboxes, and in particular to fire resistant letterboxes.

There has been a worrying increase in the incidence of arson attacks on residential and commercial properties.

Often incendiary devices are put through the letterbox of the premises. The present invention seeks to neutralise the effects of such devices. According to the invention there is provided a receptacle for use as a letterbox having first and second openings therein, wherein both openings are closable in a substantially gas tight way by flap means, and the receptacle contains fire extinguishing means that are automatically activated by sensing means when a fire takes place within the receptacle.

In preference the sensing means is a phial of liquid that breaks when the temperature around it reaches a chosen value.

Preferably, the fire extinguishing means is a rechargeable cylinder filled with a fire inhibiting substance.

Preferably, the fire extinguishing means are placed so that the fire inhibiting gas discharges into the upper part of the receptacle.

In order that the invention and its various other features may be understood more easily, an embodiment thereof will now be described by way of example only, with reference to the drawings, wherein: Fig 1 is a top perspective view of the letterbox with the flap open; Fig 2 is a sectional side view of the letterbox fixed to a door, having a letter plate and letter opening. The flap is shown in both the open and shut positions; and Fig 3 is a view from direction 3 in Fig 2, with the flap open.

The letterbox comprises a substantially oblong fireproof box 10 for mounting vertically on a door 30, having a letter plate 40 and letter opening 45 mounted horizontally in the central portion of the door 30. On one side of the letterbox is an entrance slot 11, the shape of which corresponds to that of the letter opening 45 in the door 30. The top of the letterbox forms a hinged flap 12. A knob 13 is provided to allow the flap 12 to be raised to gain access to the inside of the letterbox. When both the flap 12 and the letter plate 40 are closed the letterbox is substantially gas and liquid tight.

Mounted in the top of the letterbox is a fire extinguisher 50. The extinguisher 50 is cylindrical and is supported in a "V" shaped holder 14 that is in turn supported by a strip member 15 that extends across the top of the box 10. The length of the "V" shaped holder 14 is in excess of that of the extinguisher 50. The extinguisher comprises a cylinder 51 filled with a denser than air combustion inhibiting gas such as Halon.

The cylinder 51 is sealed by a glass phial 52 filled with yellow alcohol. The position of the extinguisher 50 and its holder 14 is configured so that there are no straight unobstructed paths through the letterbox and out of the flap 12 from the entrance slot 11.

The design of the letterbox minimises the effects of arson attacks directed at a property through the letter plate. A common mode of attack is to drop lighted rags or similar combustible material into the letterbox. The letterbox will restrict the air supply to the burning material and if the material is not burning too strongly the fire will be put out. If the material is burning strongly the air within the letterbox will heat up and circulate around the fire extinguisher 50 in the top of the letterbox. The alcohol in the phial will heat up until at a fixed temperature, preferably about 550C, the phial will burst and the combustion inhibiting gas will be released and will flood the letterbox, extinguishing the burning material. The fireproof material that the letterbox is made of protects the door and the interior of the house from the effects of the fire.Typically, the material has a relatively low thermal conductivity.

The extinguisher 50 is protected from the radiation of the flames by the shielding effect of the holder 14.

After a fire the extinguisher 50 is removed from the letterbox, refilled with combustion inhibiting gas, fitted with a new alcohol filled phial and refitted to the letterbox.

After an unsuccessful attack it is not uncommon for the perpetrator to return and make a further attack. After the burning material from the first attack has been extinguished the combustion inhibiting gas is retained inside the substantially gas tight letterbox. Any further burning material that is inserted into the letterbox during a further attack will be extinguished by this gas, thereby foiling the further attack.

Another mode of attack is to open the letter plate, use a stick or similar tool to open the flap 12 of the letterbox and then direct a burning jet of fuel or solvent from a domestic detergent bottle right through the letterbox and into the premises. In the invention the presence of the extinguisher 50 and the holder 15 make it impossible to open the flap 12 from the letter plate 45 using a crowbar or similar tool. This prevents burglars from operating door locks inside the door from the outside, through the letterbox, and gaining entry to the premises. If burning liquid is poured into the letterbox it will be safely contained and extinguished either due to lack of air or by the action of the extinguisher 50.

Apart from the stated advantages of fire resistance and additional security the letterbox also prevents pets damaging the incoming mail.

If the door is fitted with a letter plate and letter opening in which the longest edges are vertical a letterbox of the shape described is fitted horizontally, in the same relative position as described. The flap 12 is made as part of what was the side of the box 10 when it was fitted vertically to the door. The extinguisher 50 stands vertically with the alcohol filled phial 52 uppermost.

If the letter plate and letter opening are fitted horizontally in the bottom section of the door, adjacent to the door sill, then the letterbox is as described but with the entrance slot in the lower part of the box.

The box is mounted vertically on the door.

Claims

1. A receptacle for use as a letterbox having first and second openings therein, wherein both openings are closable in a substantially gas tight way by flap means, and the receptacle contains fire extinguishing means that are automatically activated by sensing means when a fire takes place within the receptacle.

2. A receptacle according to claim 1, wherein the sensing means is a phial of liquid that breaks when the temperature around it reaches a chosen value.

3. A receptacle according to claims 1 or 2, wherein the fire extinguishing means is a rechargeable cylinder filled with a fire inhibiting substance.

4. A receptacle according to any preceding claim, wherein the fire extinguishing means are placed so that the fire inhibiting gas discharges into the upper part of the receptacle.

5. A receptacle according to any preceding claim, wherein the fire extinguishing means prevent the insertion of a straight member through the receptacle, via both openings.

6. A receptacle according to any preceding claim, wherein the fire extinguishing means are protected from the effects of the fire by radiation shielding means.

7. A receptacle according to any preceding claim, wherein the receptacle is made in a fire resistant material.

8. A receptacle according to claim 7, wherein the material has a relatively low thermal conductivity.

9. A receptacle substantially as described herein with reference to, or as illustrated in, the drawings.