Steel Security Doors - Security-Rated & Fire-Rated
Supplied and Fitted Across Bristol and Nationwide
Steel security doors are the first line of defence at any point of entry — and the point where most break-in attempts either fail outright or get through in seconds, depending on what’s actually fitted. A timber, uPVC or composite door can be levered, drilled or kicked through with hand tools in under a minute. A correctly specified steel door-set, fitted to a steel frame with the right locking mechanism, is built and tested to resist exactly that.
Thornhill Security has been supplying and fitting steel doors across Bristol and the South West for over 50 years, and we now deliver and install steel security doors nationwide. We stock the Strongdor range — door-sets independently tested and certified to LPS 1175, Secured by Design and WarringtonFire standards — and every installation is carried out by our own in-house, MLA-approved team. We don’t sub-contract fitting out, which means the people who size up your opening are the same people who hang the door.
Whether you need a personnel door for a fire exit, a thermally insulated external door, or a high-security rated door designed to resist a sustained, tool-based attack, we’ll help you specify the right door for the actual risk to your building — not just the most expensive one.
Who Needs a Steel Security Door?
Steel security doors are specified wherever a building has a point of entry worth protecting properly — internally or externally. We supply and fit doors for:
Shops, Retail & Jewellers
Rear entrances, stockrooms and back-of-house access points.
Public Sector & Local Authority Sites
Compliant, certified door-sets for tendered specifications
Schools, Colleges & Universities
Communal entrances, plant rooms, restricted-access zones.
Offices & Commercial Premises
Reception entrances, server rooms, comms cupboards.
Warehouses & Logistics
Personnel doors alongside roller shutters, high-traffic fire exits.
Pharmacies & Healthcare
Controlled-drug storage areas, secure stock rooms.
Landlords & Residential Blocks
Communal entrance security and fire exit compliance.
Religious & Community Buildings
Securing unsupervised premises out of hours.
Need a door for a building type not listed here? Call us on 0117 967 4994 — if we haven’t fitted one already, we’ll tell you honestly whether a steel door is the right solution before we quote.
Our Range of Steel Security Doors
Features and Benefits of Steel Security Doors
A correctly specified steel door-set outperforms timber, uPVC and composite alternatives in every measure that matters for a commercial or high-traffic residential entrance:
- Security — Reinforced steel leaf and frame, anti-jemmy lip to resist crowbar attack, drill-resistant cylinders and a flat stainless steel threshold. Available certified up to LPS 1175 SR4.
- Locking — From single-point night latches through to multi-point locking mechanisms — whether that’s multiple locks on a door or a single lock with multiple locking points — specified to match the door’s security rating and your day-to-day access needs.
- Fire Performance — Steel doors can be certified for fire resistance independently of their security rating — see the section below for FD ratings.
- Low Maintenance — Galvanised steel construction means these doors don’t warp, rot or crack, and most carry a 5–10 year paint guarantee on their coating — far less upkeep than repainting or resealing a timber door.
- Thermal & Acoustic Insulation — Insulated door-sets reduce heat loss and external noise transfer. Our Steeldor Thermal Door, for example, uses an insulated Rockwool core to achieve a U-value as low as 1.5 W/m²K.
- Appearance — Available in a wide range of RAL colours, glazed vision panels, louvred ventilation panels and finishes, so a security door doesn’t have to look like one.



Fire Protection & Safety Features
Security and fire performance are tested and certified separately — a door can be security-rated, fire-rated, or both. Fire-rated steel doors are typically classified by how long they hold back fire and smoke, expressed as FD ratings (for example FD30 for 30 minutes of integrity, up to FD120 for higher-risk applications).
Security and fire performance are tested and certified separately — a door can be security-rated, fire-rated, or both. Fire-rated steel doors are typically classified by how long they hold back fire and smoke, expressed as FD ratings (for example FD30 for 30 minutes of integrity, up to FD120 for higher-risk applications).
We have a full range of fire exit steel security doors and can advise on the correct fire rating for your building during your site survey, alongside professional installation for every product we supply.
Common Steel Secrity Door FAQs
We’ve answered the questions we’re asked most often by customers enquiring about steel security doors. If we haven’t covered yours, call us on 0117 967 4994.
The right door depends on what you’re protecting and how the door will be used — not just the type of building it’s going into. Specifying too low a rating leaves a real vulnerability; specifying too high adds cost for no benefit. In practice, the choice usually comes down to a handful of factors:
- What’s behind the door
- Whether it’s part of a fire escape route
- Internal or external use
- How many people need access, and how often
- The building itself
- Accessibility requirements
Rather than guess at this from a product page, we talk it through with you during a free site survey, so the door you order matches the actual risk to your building — call 0117 967 4994 to arrange one.
It refers to LPS 1175, the UK testing standard that certifies how long a door withstands a defined, timed attack using specific tools. Ratings run from SR1 (basic opportunist attack) up to SR4 (sustained attack with power tools). The right rating depends on what’s behind the door, not just the building type.
They’re tested and certified separately. A security rating (LPS 1175 SR1–SR4) measures resistance to forced entry; a fire rating (FD30 to FD120 and above) measures how long a door holds back fire and smoke. Many steel doors — including those we supply — can be certified for both, which matters if the door also sits on a fire escape route.
Yes — steel door-sets are made to measure, so unusual heights, recessed entrances, or openings that need redesigning rather than just a new door can all be accommodated. We’ve built a custom 2m-high frame with a fixed panel above it to stop a door being climbed, and brought a recessed, hard-to-see entrance forward to remove a blind spot for staff.
Yes. Doors can be specified with low-level vision panels for wheelchair users, DDA-compliant (Equality Act) thresholds, and the correct opening direction to meet fire escape requirements. We carried out exactly this kind of upgrade — replacing a non-compliant inward-opening door with an accessible, fire-compliant steel door fitted with a push-to-exit mechanism.
Yes. We fit panic hardware — push pads or push bars — to steel doors used as fire exits, allowing single-action escape from inside while keeping the door secure from outside. This is standard for warehouses, schools, offices and public-facing premises.
Steel security doors can be fitted with a range of locking options, from a single-point lock right through to multi-point locking — either multiple locks fitted to the door, each throwing a single bolt, or a single lock with multiple locking points built in. Which approach suits you depends on the door’s security rating and how it’s used day to day. We can also specify digital and electronic locking where you need integration with an access control system or a master key system. Our team will recommend the right configuration during your site survey rather than defaulting to the most complex option.
Real Steel Security Door Installations
Specification advice only means something if it’s backed by real installations. Here are a few projects our team has completed — each one solving a different problem with a steel door.

Bringing an external door up to accessibility and fire standards
A client's inward-opening external door had no vision panel, leaving people on either side unable to see each other — and its inward-opening design meant it didn't meet fire regulations or Disability Discrimination Act (DDA) requirements. We replaced it with an outward-opening steel security door fitted with two vision panels (including a lower panel for wheelchair users), a DDA-compliant threshold, and a push-to-exit mechanism for safe, easy egress.

Improving a recessed, hard-to-see entrance
A former warehouse, converted into office space, had its entrance set back in an alcove — out of sight from the road and making staff feel unsafe arriving and leaving. We brought the entrance forward in line with the wall, removing the alcove entirely, and fitted a black powder-coated steel door with a custom panel painted to match the original archway.
Get a Competitive Steel Security Door Quote
Leave your details and we’ll respond within 24 hours to arrange your free site survey — covering Bristol, the South West, and nationwide installations.
Testimonials
Why Choose Thornhill Security?
- A fast, local service, dealing with one contractor from start to finish.
- We only use our in-house team and don’t sub out our work
- We are MLA approved locksmiths
- We have relationships with all leading manufacturers
- We are a Government approved supplier and have the following accreditations (SafeContractor, Construction Line, BSVTA, MLA).

























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