Blast ratings: ISO 16933

ISO 16933 is the international standard for blast resistant glazing. It grades how glazing and its frame stand up to a vehicle bomb, using EXV classes for the charge and stand-off distance, SB classes for satchel charges, and an A to F hazard rating. Match the EXV, SB and hazard ratings to the threat assessment.

• EXV45 to EXV10Vehicle bomb classes to ISO 16933
• 100 kg TNT equivalentThe test charge for EXV classes
• A to FHazard rating for the glazing
• SB classesFor hand-carried satchel charges

What ISO 16933 is and who publishes it

ISO 16933 is an international standard for the blast testing of glazing. It is published by ISO, the International Organization for Standardization, and adopted in the UK through BSI. It covers one specific threat: the effect of an explosion on glass and the framing that holds it.

The standard deals with two kinds of explosive attack. The EXV classes cover vehicle bombs, modelled as a charge equivalent to 100 kg of TNT at a defined stand-off distance from the glazing. The SB classes cover hand-carried satchel charges, a smaller and closer threat. Both are tested against complete glazed assemblies, not panes of glass on their own.

Alongside the EXV or SB class, every result carries a hazard rating from A to F. This letter describes what the glazing did in the test: whether it stayed intact, cracked, or threw fragments into the room. The class tells you the severity of the attack; the hazard rating tells you the consequence for the people behind the glass. A specification needs both.

The EXV classes: vehicle bombs at a distance

The EXV classes are named for the stand-off distance in metres between the charge and the glazing. The charge is equivalent to 100 kg of TNT in every case; what changes is the distance. The table below lists the full scale.

The key point is the direction of the scale: a lower number means a more severe test. EXV10, with the charge at 10 metres, is the hardest EXV class to pass, because the pressure wave arrives stronger at close range. EXV45, at 45 metres, is the easiest. This catches people out, so it is worth stating plainly on every specification: EXV10 is the top of the scale.

Choosing the class starts with the site. The stand-off distance is a physical fact about the building: how far a vehicle could get from the glazed facade. A building set back behind a wide plaza may only need a modest class; a facade on the street line needs the severe end. The threat assessment and the site layout together fix the class, and the specifier writes that class into the glazing requirement.

Lower number, harder test. In the EXV scale the number is the stand-off distance in metres, so EXV10 is the most severe class and EXV45 the least. State the direction on the specification to avoid confusion.

SB classes and the A to F hazard rating

The SB classes cover hand-carried satchel charges: smaller devices brought close to the glazing by a person on foot. They complement the EXV vehicle-bomb classes, and a site facing both threats may need glazing rated under both. As with EXV, the result is only meaningful for the tested assembly of glass, frame and fixing.

The hazard rating runs from A to F and describes the outcome for the room behind the glass. The table below sets out what the letters mean.

In practice, specifiers aim for the low end of the scale. A result of A means the glazing held; F means it produced a dangerous shower of fragments. The acceptable letter depends on what is behind the glass: an occupied office, a public concourse or a protected space each argue for the best achievable hazard rating at the required EXV class. State both the class and the acceptable hazard letter in the specification, for example “EXV25 with hazard rating B or better”.

How the blast test works

In the ISO 16933 test, a charge equivalent to 100 kg of TNT is detonated at the stand-off distance for the class being tested. The test specimen is a complete glazed assembly: glass, frame, beading and fixings, put together as it would be on site. Instruments and observers record what happens to the glazing and, critically, what enters the room behind it.

The result has two parts. First, the EXV class the assembly withstood: the charge distance it was tested against. Second, the hazard rating from A to F, describing the breakage and fragment behaviour. Both are needed to describe the performance. An “EXV25” result with hazard rating F is a very different outcome from “EXV25” with hazard rating A, and the specification must distinguish them.

Because the specimen includes the frame and fixings, the test exposes the usual failure modes: glass pulling out of the bead, frames distorting, fixings letting go. A pane that survives while its frame fails is a failed assembly. This is why blast ratings, like all the ratings on this site, belong to tested constructions, and why the test evidence must be checked against the submittal.

How to read a blast rating

A blast rating reads as a class plus a hazard letter, for example “EXV25, hazard rating C”. The class names the attack the glazing was tested against: a 100 kg TNT equivalent charge at 25 metres. The letter names the outcome for the people behind the glass. Read the two together; either one on its own is half the story.

Remember the direction of the scale. EXV10 is more severe than EXV45, and hazard rating A is better than hazard rating F. When comparing two offers, the stronger result is the lower EXV number combined with the earlier hazard letter. Write both into the specification so that tender returns can be compared like for like.

Check the scope of the evidence. The rating covers the glazing in its tested frame, so the certificate should name the glass make-up, the frame section, the beading and the fixing method. If the submittal changes any of those, the rating strictly no longer describes the supply. Our blast resistant glass page explains how the glass and frame work as a system.

How ISO 16933 compares with related standards

Blast is one of three violent threats a facade may face, alongside gunfire and forced entry, and each has its own standard. The table below separates the three.

EN 13123 and EN 13124 are the European blast standards for doors, windows and shutters. They use a different classification: EPR1 to EPR4 from shock tube testing and EXR1 to EXR5 from range testing. A project may call for ISO 16933 on the glazing and EN 13123/13124 on the doorsets, or it may standardise on one route. Either way, the specifier should name the standard explicitly rather than writing “blast rated” and hoping the supply matches the intent.

Ballistic and forced-entry ratings do not imply blast performance. A window tested to EN 1522 FB6 has proved it stops rifle fire, not that it survives a pressure wave; a doorset rated to LPS 1175 SR4 has proved it resists tools for minutes, not that it holds against a charge. Where the assessment names several threats, choose a product tested to every relevant standard. Our ballistic ratings guide and LPS 1175 guide cover those systems.

How to specify a blast rating

1. Establish the threat. Confirm whether the assessment calls for vehicle bomb, satchel charge, or both.
2. Fix the stand-off distance. Measure how close a vehicle could get to the glazed facade from the site layout.
3. Choose the EXV class. Select the class that matches the stand-off distance; remember that EXV10 is the most severe.
4. State the hazard rating. Name the acceptable hazard letter, based on what sits behind the glass.
5. Require the tested assembly. Specify glass, frame, beading and fixings as one tested construction.
6. Check the test report. Insist on the ISO 16933 report naming the class, the hazard rating and the exact construction.

A clean specification line reads: “Glazing tested to ISO 16933, EXV25, hazard rating B or better, supplied and installed as the tested assembly.” That single line fixes the standard, the class, the acceptable outcome and the scope of supply, and it gives everyone from the architect to the site checker the same thing to verify.

Products rated to ISO 16933

ArxBridge supplies blast protection across glazing, windows, doors and facades. Blast resistant glass is laminated glazing matched to its frame. Blast resistant windows are framed systems carrying hazard ratings, and blast resistant doors are EXV rated steel doorsets. Blast rated curtain walling takes ISO 16933 testing across glazed facades, and residential blast protection covers high-risk homes. For existing buildings, blast protection window film is a retrofit option that holds fragments, though it is not a substitute for a tested EXV assembly. Sectors that specify blast ratings include government and defence, transport hubs and utilities and energy.

Frequently asked questions