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In buildings where security is critical, the door is often one of the most vulnerable points in the building envelope. Data centres, banks, government and political buildings, critical infrastructure facilities and other high value premises require more than a conventional steel door: they need a security doorset that has been independently tested against defined forced-entry threats. For architects, specifiers and building companies, LPS 1175 provides one of the most important benchmarks for specifying resistance to forced entry. Within the standard, SR2, SR3 and SR4 represent progressively higher levels of protection, with each rating reflecting both the tools available to an attacker and the time for which the doorset must resist the attack. The current version is LPS 1175: Issue 8.2, published by BRE Global and used within the LPCB certification scheme. High Security Doors: What is LPS 1175?LPS 1175 is a Loss Prevention Standard for the testing and classification of intruder resistant building components. It applies to a wide range of products, including hinged and pivot doors, sliding doors, shutters, grilles, windows, walls, partitioning and other security barriers. Importantly, LPS 1175 does not simply test the thickness of a steel door or the strength of its lock. The complete security assembly is assessed. This can include the door leaf, frame, locking arrangements, hinges, glazing, louvres and associated hardware. The installation and fixing method specified by the manufacturer are also assessed. This is an important distinction when specifying a high security doors. A strong door fitted into a weak frame, wall or fixing arrangement does not provide a genuinely secure opening. LPS 1175 therefore treats the doorset as an integrated system rather than rating individual components in isolation. How do SR2, SR3 and SR4 differ?Under LPS 1175 Issue 8.2, security classifications use two elements: a letter identifying the threat/tool category and a number representing the tested delay period. The commonly used SR terminology corresponds to the following classifications:
The rating is not simply a measure of elapsed time. It combines the type and capability of tools used, the number of attackers and the working time achieved during the test. For SR2, SR3 and SR4, testing involves a single attacker; the permitted tool mass and capability increase as the security rating rises. To illustrate this:
SR2 – B3SR2 represents a significant step above basic security protection. The B tool category builds on the tools used for the lower A category and introduces additional equipment, including a small battery-powered drill, bolt cutters, a claw hammer, hacksaw and tools offering greater mechanical advantage. The standard describes Category B as representing a more determined opportunist attack using bodily force and tools with greater mechanical advantage. The corresponding B3 classification is SR2, with a three-minute working-time classification. For a project, SR2 may be appropriate where the objective is to protect controlled areas from opportunistic or determined unauthorised entry without the threat profile associated with highly experienced attackers. SR3 – C5SR3 increases both the sophistication of the test and the available attack options. The C tool category adds tools such as an axe, 12 V drill, larger bolt cutters, crowbar, chisels, hammer and other equipment. BRE describes Category C as being intended for deliberate forced entry of well-protected premises using bodily force and a wide selection of attack options. A C5 classification corresponds to SR3, requiring the product to withstand the defined attack for five minutes of working time. SR3 can therefore be considered where the building or room contains assets, information or infrastructure of greater importance and the anticipated threat is more deliberate than a conventional opportunistic break-in. SR4 – D10SR4 represents a further increase in resistance. The D category builds on the preceding tool categories and introduces more substantial equipment, including higher-capacity battery tools, grinders, jigsaws, larger bolt cutters, lock-removal tools, heavy-duty bars, sledgehammers and other equipment. BRE defines Category D as being intended for experienced attempts at forced entry. The corresponding D10 classification is SR4, with a ten-minute working-time classification. For architects and security consultants, SR4 is consequently a significant choice when protecting high-value or high-consequence areas where a greater level of deliberate attack resistance is required. Why steel doors are suited to high-security applicationsHigh-security steel doors can provide a robust physical barrier while still being engineered to accommodate the operational requirements of a modern building. Depending on the product and certification, a security doorset may incorporate:
However, these features should not be assumed simply because a door is described as a “high-security steel door.” The relevant LPS 1175 certification should be checked for the exact product configuration. LPS 1175 specifically assesses the product as an assembly. It does not assign an independent LPS 1175 rating to an individual lock, sheet of steel or piece of glazing. Where might SR2, SR3 and SR4 be specified?There is no universal rule that a particular building type automatically requires a particular SR rating. The appropriate rating should follow a security risk assessment and the characteristics of the threat. Nevertheless, the ratings can help establish a useful hierarchy when developing a security strategy. SR2: controlled commercial and operational areasSR2 can be considered for areas where protection against determined opportunist attack is required. Potential applications may include:
SR3: higher-value and sensitive areasSR3 provides a higher level of forced-entry resistance and may be considered for more sensitive locations, such as:
SR4: high-security and high-consequence areasSR4 is intended for a substantially more capable attack scenario and can be considered for areas where a prolonged and experienced forced-entry attempt represents a credible threat. Potential applications include:
These are examples rather than automatic requirements. The National Protective Security Authority (NPSA) emphasises that forced-entry standards should be selected according to the specific threat, the type of product being protected and the required level of protection. NPSA The importance of specifying the complete doorsetOne of the most common specification errors is to focus exclusively on the door leaf. For LPS 1175, the security performance belongs to the tested configuration. Changing the frame, lock, glazing, hardware or installation arrangement can potentially affect the certified performance. For this reason, a specification should identify:
The substrate is particularly important. LPS 1175 assumes that the structure to which the product is fixed provides resistance at least equivalent to that of the product itself. In other words, specifying an SR4 doorset does not solve a security weakness in a lightweight or inadequately designed surrounding wall. Security should be considered alongside fire and life safetyA high-security door is rarely specified for security alone. In a data centre, for example, the same opening may need to provide forced-entry resistance, fire resistance, smoke control, controlled access, emergency egress, acoustic separation and frequent operational use. These requirements need to be coordinated from the beginning of the design. LPS 1175 is primarily an intruder-resistance standard. It does not itself provide classifications for fire resistance, acoustics, durability, weather performance, ballistic resistance, explosion resistance or vehicle impact. These characteristics need to be addressed through the relevant standards and project specifications. This is particularly important for doors incorporating electronic access control. LPS 1175 does not assess every form of electronic manipulation, so electronic components should also be selected and assessed against the appropriate operational and safety requirements. LPS 1175 versus EN 1627Architects and specifiers may also encounter EN 1627, which classifies burglar resistance using Resistance Classes (RC). These standards should not be treated as interchangeable. BRE explicitly states that there is no direct correlation between the performance classifications of LPS 1175 and other forced-entry standards, including EN 1627, LPS 2081, LPS 1673 and PAS 24. Therefore, a specification should not simply state “SR3 or equivalent EN 1627 class” unless a suitably qualified security professional has established that the alternative standard addresses the same threat scenario. The NPSA similarly recommends selecting the standard that most closely reflects the characteristics of the threat being addressed. NPSA What should architects and specifiers ask suppliers?When comparing high security steel doors, the following questions can help avoid ambiguity:
The LPCB RedBook provides listings of certified security doorsets and identifies the relevant product configuration and security rating. Getting the specification rightFor high-priority buildings, security should be designed into the project rather than added at the end. The choice between SR2, SR3 and SR4 should begin with the threat assessment and the value or consequence associated with unauthorised access. From there, the security rating can be A useful approach is to think of the three ratings as a progression: SR2 → SR3 → SR4 Increasing attacker capability + increasing tested delay = increasing forced-entry resistance. The important point is that a higher rating is not automatically better for every opening. A higher-security doorset can introduce greater For architects, specifiers and building companies, an independently tested LPS 1175 doorset provides a much more meaningful basis for security specification than descriptions such as “heavy-duty,” “rein When the building contains critical information, infrastructure, financial assets or sensitive operations, the right question is therefore not simply “How strong is the door?” but: “What level of attack is the doorset designed and independently tested to resist?” That is where SR2, SR3 and SR4 and the wider LPS |
