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Intumescent Metal Fire box

Product 52

52 – firebox on door 2

Fire and smoke resistant letter bags and boxes to protect against arson

Not available to purchase online.

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Intumescent Metal Fire Box

An internal intumescent metal fire box suitable for use in areas with vulnerability to arson or vandalism attacks. The intumescent expands under heat and contains fire spread, which will stop fires. This product is safe to use as it does not contain liquids or gasses. Also available as an intumescent flexible fire bag.

Burning paper and liquids put through mail apertures in doors and walls can have devastating consequences. Nocturnal arson attacks on homes can be particularly worrying for domestic residents. The Envirograf rigid firebox protects mail slots, so homes and businesses have the confidence that their premises will remain safe against damaging and disruptive arson attacks. The metal firebox fits onto the back of the door or wall. Intumescent material will extinguish the fire, which can be easily renewed. Rigid metal fireboxes come with a hinged lid and flush lock as standard. A hinged front door is available as an optional extra.

Tested to BS476 Part 22 (1987). Fireboxes and bags self extinguish flames and fire, so will not allow anything to burn.

Our products upgrade doors to Fire Door rating, in compliance with Building Control. Browse our full range of Fire Door products and Fire Door Accessories online.


– Internal intumescent material will extinguish any combustible items dropped into the box or bag, and can be easily renewed
– The flexible fire containment bag can be compressed and is for use where doors open tightly against walls

Application Instructions

Metal Boxes:
Simply screw into position using 30mm screws

Flexible Fire Bags:
The Flexible Fire Bag has an oversized letter box opening to go over existing internal openings
or flaps. The pack is supplied with a small tube of Fire Proof Silicone, which can either be
squeezed over the external plate or around the internal side of the door, around the letter box
opening. Open the lid by turning the clips and separating the Velcro tape. There are two holes
at either end of the metal plate, simply screw to the door with the screws supplied.

Case Studies

  • It's ‘bin’ a burning desire at King Street

    Intumescent fire containment box providing protection for public bus station bin at King Street, Mildenhall, Suffolk.

Order References / Sizes

REF                        A (Wall/Door height)           B (Outside height)              C (Depth)                              D (Width)               


Flexible bags with horizontal letter opening:–

FLEX1                    335mm                                  335mm                                  130mm                                  420mm

Aperture size 315mm x 70mm.

FLEX2                    335mm                                  335mm                                  130mm                                  420mm

For UPVC Doors. Aperture size 330mm x 55mm. Single layer of cloth.

FLEX3                    260mm                                  260mm                                  095mm                                  400mm

For UPVC doors. Aperture size 290mm x 55mm.

FLEX3/A                260mm                                  260mm                                  095mm                                  400mm

For UPVC doors. Aperture size 315mm x 70mm.


Flexible bags with vertical letter opening:–

FLEX4V                 560mm                                  560mm                                  130mm                                  360mm

Aperture size 315mm high x 70mm wide.

FLEX5V                 530mm                                  530mm                                  100mm                                  300mm

Aperture size 290mm high x 55mm wide.


Rigid metal boxes:–

FB1                        360mm                                  300mm                                  170mm                                  375mm

FB2                        360mm                                  300mm                                  090mm                                  375mm

FB3                        360mm                                  300mm                                  200mm                                  400mm

FB4                        675mm                                  600mm                                  300mm                                  600mm


Standard spouts/chutes up to 300mm long and at an angle of 30 degrees to the horizontal, to pass through walls, can be fitted to rigid boxes at an extra cost. If you require spout/chute lengths greater than 300mm, please ask for a special price to be quoted. Flush locks are included. Standard colours are white, black, and brown. Other colours are available at extra cost. Use a letter box liner with any letter plate on the front of the door. Other box sizes can be made to order.