Blast Resistance: Standards, Ratings and Certified Products for UK Critical Infrastructure

What Is Blast Resistance?

Blast resistance is the measured ability of a building component, such as a door, window, glazing panel or curtain wall system, to withstand the pressure wave generated by an explosion. When a bomb detonates, it produces an extremely rapid and powerful positive-phase overpressure followed by a negative-phase suction. This combination can cause catastrophic structural failure, propel glass fragments at lethal velocity into occupied spaces and structurally compromise an entire building envelope.

A blast resistant product is one that has been independently tested against a defined explosive charge at a specified standoff distance and shown to perform within defined hazard limits. The result is a rated classification, issued by the certifying body, that tells a specifier precisely what threat the product has been verified to resist.

Blast resistance is a separate performance criterion from forced entry resistance and ballistic resistance. A product holding an LPS 1175 forced entry rating is not automatically blast rated, and a product with a ballistic rating to EN 1522 is not automatically certified against blast. Each discipline requires independent testing under its own standard. High-security installations protecting critical infrastructure frequently specify all three to ensure comprehensive protection against the full range of credible threats.

Who Needs Blast Resistant Doors, Windows and Glazing?

Blast protection is a requirement wherever the credible threat includes an explosive device, whether from terrorism, industrial accident or conflict. The following sectors routinely specify blast resistant building products:

• Government & Public Buildings
• Embassies & High Commissions
• Military Installations & MOD Facilities
• Critical National Infrastructure (CNI)
• Power Generation & Utilities
• Petrochemical & Oil Refinery
• Data Centres & NDIS Sites
• Transport Hubs & Airports
• Financial Institutions
• Courts & Justice Buildings
• Police & Border Control
• High-Security Commercial

Threat assessments for these buildings are typically conducted by qualified security consultants in collaboration with the NPSA (National Protective Security Authority), formerly CPNI. The outcome of that assessment will define the blast standard and rating classification required, which in turn drives product selection and specification.

Blast Resistance Standards Explained

Three primary standards govern blast resistance testing and classification for building products in the UK and Europe. Each covers a different scope, uses a different test method and produces a different rating format. Understanding which standard applies to your project is essential before specifying products.

ISO 16933: Counter-Terrorism Blast Glazing Standard

ISO 16933:2007 (confirmed 2023) is the most widely specified blast glazing standard for counter-terrorism applications in the United Kingdom. It tests glazing systems against open-air detonations using real explosive charges, making it the most realistic of the available blast testing methodologies. The results are presented as a two-part classification combining a severity level (the number) and a hazard rating (the letter), both of which are essential to understanding what a product actually delivers.

EXV Ratings: Vehicle Bomb Classifications

EXV ratings address the threat from vehicle-borne improvised explosive devices (VBIEDs), based on a 100kg TNT-equivalent charge detonated at varying standoff distances. The lower the standoff distance, the more severe the blast loading and the harder the test.

SB Ratings: Satchel Bomb Classifications

SB ratings address hand-carried devices placed in close proximity to a building. The charges range from 3kg to 20kg TNT equivalent at standoff distances from 3m to 9m, representing the threat profile of a device placed against or near a building entrance.

ISO 16933 Hazard Ratings: The Letter Is as Important as the Number

A product's ISO 16933 rating is only complete when the hazard letter is included alongside the severity number. A rating of EXV25(C) and EXV25(F) represent radically different outcomes for the people inside the building, even though both were tested at the same blast level. The hazard rating is a direct measure of occupant safety.

For most UK counter-terrorism specifications, the minimum acceptable outcome is a hazard rating of C (Minimal Hazard). Government buildings, embassies and high-security facilities frequently require A or B. Ratings of E and F are considered failures in occupied building contexts and should not appear in a valid specification.

Example: A product specified as EXV25(C) has been arena-tested against 100 kg TNT at 25 m standoff and achieved minimal hazard, meaning the inner glazing face was substantially retained with only minor fragmentation. This is a meaningful, verifiable guarantee of performance, not a marketing claim.

EN 13123 / EN 13124: Complete Assembly Blast Standard

Where ISO 16933 classifies glazing performance, EN 13123 and EN 13124 classify the complete fenestration assembly, including the frame, fixings, infills, hardware and seals. This is the correct standard to reference when the specification requires certification of the entire installed product rather than the glazing material alone.

The standard is divided into two parts depending on test method. Part 1 uses a shock tube to simulate explosion pressure in a controlled laboratory environment. Part 2 uses open-air arena testing with real explosive charges. Both parts use separate rating scales and are not directly comparable.

EPR Ratings: Shock Tube Classification (EN 13123-1 / EN 13124-1)

EPR (Explosion Pressure Resistance) ratings are produced by shock tube testing and are expressed in bar. They are commonly used for industrial and petrochemical blast specifications where the slower-rising pressure profile of a confined deflagration is more relevant than a counter-terrorism detonation scenario.

EPR ratings may carry an S (splinters) or NS (no splinters) suffix indicating whether material came off the protected face during the test. NS is the higher classification and is typically required where personnel are present behind the assembly.

EXR Ratings: Arena Classification (EN 13123-2 / EN 13124-2)

EXR ratings are produced by open-air arena testing using real explosive charges at defined standoff distances. They address the more intense, rapidly-rising pressure profile of a detonation event and are applicable to counter-terrorism scenarios where a whole-assembly rating is required alongside or instead of a glazing-only ISO 16933 rating.

EN 13541: Glass-Only Explosion Resistance Standard

EN 13541:2012 is a shock-tube standard for testing a single pane of glass in a rigid frame. It produces ER1 to ER4 ratings, each with an S or NS suffix, and is primarily used for glazing material qualification and product development rather than for specifying whole-system performance on a live project.

Because EN 13541 tests only a glass pane in an idealised rigid frame, it does not capture the real-world interaction between glazing, frame, fixings and substrate that determines how a product actually performs in an installation. For project specifications requiring reliable blast performance assurance, ISO 16933 or EN 13123/13124 provides the more appropriate reference, as both can certify the complete installed assembly.

Choosing the Right Blast Standard for Your Project

Understanding which standard to specify is as important as understanding what the rating means. The three standards address different threat scenarios and different scopes of testing. The table below provides a direct comparison to assist specifiers in selecting the correct reference for their project.

For most UK counter-terrorism specifications driven by an NPSA-aligned threat assessment, ISO 16933 is the appropriate standard for glazing performance and EN 13123-2 / EN 13124-2 is the appropriate standard where whole-assembly certification is required. For industrial applications such as oil and gas or petrochemical processing, EN 13123-1 / EN 13124-1 (EPR ratings) is the standard most commonly referenced in design briefs.

Why Independent Blast Testing Matters

Blast resistance cannot be assessed by calculation alone. A building product must be physically subjected to explosive loading and its performance observed and classified by an independent accredited testing facility. Only then can a manufacturer legitimately state that a product holds a defined blast rating.

At Premier Security Ballistic & Blast Ltd, all blast ratings are obtained through independent third-party testing at recognised facilities. We do not self-certify. Every rated product is supported by a formal test report from the testing body, which can be provided to specifiers, project managers and security consultants as part of the product submission package.

What Independent Testing Provides

• A verified blast rating from a recognised accredited facility
• A formal test report covering the exact tested configuration
• Confidence for specifiers, clients and insurers that performance has been proven, not estimated
• A clear scope-of-supply definition, including frame, fixings, glazing build-up and substrate
• Traceability in the event of an insurance or regulatory audit

Blast, Ballistic and Forced Entry: Combined Protection

Many of the facilities that require blast resistance also require protection against ballistic attack and forced entry. Critical national infrastructure sites, government buildings, embassies and military installations regularly specify products that have been independently certified across all three disciplines.

Premier Security Ballistic & Blast Ltd manufactures products that can hold simultaneous certification to:

• Blast resistance to ISO 16933, EN 13123 or EN 13541
• Ballistic resistance to EN 1522 / EN 1523 and EN 1063 (FB1 to FB7)
• Forced entry resistance to LPS 1175 (SR1 to SR8)
• Fire resistance to BS EN 1634 and relevant national standards

Each certification is obtained separately through independent testing. Combined ratings confirm that a single product has been verified against all specified threats without any certification implying another. This allows specifiers to identify a single product that satisfies multiple lines of a security schedule rather than relying on a composite assembly of separately sourced and unvalidated components.

For further information on our ballistic ratings, see our Ballistic Resistance guide. For forced entry ratings, see our LPS 1175 guide.

Frequently Asked Questions: Blast Resistant Products

Related Premier SSL Resources

• Blast Resistant Doors — product specifications and available ratings
• Blast Resistant Windows — product specifications and available ratings
• Blast Resistant Glazing — glazing systems and ISO 16933 classifications
• Blast Resistant Curtain Walling — facade systems for CNI
• Ballistic Resistance — EN 1522 / EN 1063 ballistic ratings explained
• LPS 1175 Security Ratings — forced entry resistance explained
• Contact Premier SSL — technical consultation and project enquiries