Impact resistance in glass doors: Understanding performance, safety and compliance

Glass doors have many qualities that make them attractive for specification in both domestic and commercial environments. External glass doors bring welcome extra daylight into buildings and provide continuity with the glazing elements of domestic conservatories and glass extensions as well as the glass facades of office and commercial buildings. Internal glass doors and glass partitions provide a visual connection between spaces, make the rooms seem more spacious and can create a more pleasant atmosphere in which to work, relax or play.

Like any construction material used in such vast quantities, and in so many varied applications, glass needs to demonstrate that it complies with all the relevant building regulations. The regulations and standards are in place to ensure that products such as glass doors meet specific performance criteria. In this way they can demonstrate they are safe to meet the demands of the environment into which they are specified. The requirements for impact resistance are heightened in high-traffic areas of public buildings and in places with children and vulnerable people such as schools and hospitals.

Safety glass refers to glass designed with additional safety features that reduce the risk of injury when it breaks. There are two main types of safety glass:

• tempered glass
• laminated glass

The distinct breakage behaviours of tempered and laminated glass are key considerations when selecting glazing materials in glass doors to enhance the safety of people using them. Impact-resistant glass is a type of security glass designed to be resistant to shattering. This allows it to resist attack from ‘smash-and-grab’ thieves or from attempts to gain forced entry through the glazed panel of a glass door.

Since the performance requirements of impact-resistant glass vary depending on its application, specifiers need a reliable method to ensure that the glass selected is appropriate for its intended use.

There are two ways of testing the glass for its impact resistance, either using a soft body or a hard body. 

To determine whether the glazing in a glass door is appropriate for a particular application it is important to understand these tests and their results.

The glass is tested by following the standard BS EN 12600 – ‘Glass in building. Pendulum test. Impact test method and classification for flat glass’ 1 . The test setup consists of a soft-bodied impactor made of two tyres fitted to the rims of wheels that carry two steel weights of equal mass. The total weight of the impactor is 50 kg.

This soft-bodied impactor is designed to simulate the impact of a human body. The impactor’s weight distribution and flexibility are engineered to ensure that the test is both realistic and reproducible. During testing, the impactor is released from one of three standardised drop heights of 190 mm, 450 mm and 1200 mm onto a standard-sized (876 mm by 1938 mm) pane of the glass to be tested. This glazing is secured in a rigid test frame.

1 https://knowledge.bsigroup.com/products/glass-in-building-pendulum-test-impact-test-method-and-classification-for-flat-glass

The impact resistance classifications of glass under BS EN 12600 are based upon the height from which the soft body weight drops and the type of breakage that occurs.

The highest performance classification is Class 1 as it is based on the highest test height drop. The classes and typical uses are outlined in the table below.

Understanding how glass breaks under impact is essential for ensuring safety and selecting appropriate glazing materials. EN 12600 identifies three distinct breakage modes.

The hard body test involves dropping a 4.11 kg steel sphere onto the glass to assess its strength and resistance. This simulates someone trying to smash glazing to gain entry to a building. The sample of glass fails if it is penetrated by the impact of the sphere before five seconds has elapsed after the initial impact.

Each sample is tested by dropping the sphere three times on different areas of the glass sample, once at each point of a triangular arrangement of set dimensions. The highest category is P5A. This indicates resisting penetration of the ball dropped from the greatest height and resisting an extra six strikes of the steel ball rather than the three strikes of the categories P1A to P4A. The categories are listed in the table below.

Whereas the steel ball hard body test simulates a smash-and-grab attack with a blunt instrument, the axe test detailed in EN 356 is designed to assess the resistance the glass can offer against a determined attack with a heavy sharp tool.

A glass sample is subjected to attack by a hammer and an axe. The test rig is designed to ensure that a set and consistent velocity and energy of strike is repeated until the glass is penetrated. The category of resistance is taken from the number of strikes needed before the sample fails.

If you are specifying glass doors in new residential buildings in the UK, they must meet the requirements of PAS 24 3 to align with Approved Document Q - ‘Security in dwellings 4 ’ of the building regulations. This Publicly Available Standard (PAS) defines a series of tests designed to evaluate the security of doors and windows against opportunistic intruders. It is not intended to defend against professional burglars.

The tests assess both the tools used and the time it would take for an attack to be noticed. Components such as profiles, frames, hardware, handles, locks, cylinders and glass are all tested for resistance to forced entry. Testing methods include:

• Mechanical load testing with hydraulic rams to attempt to force doors open.
• Soft impact testing using 30 kg sandbags swung against doors to simulate impact.
• Hard body impact testing with a 50 kg steel impactor to evaluate hinge and lock strength.

In addition to security, PAS 24 also demonstrates that the product meets relevant BS EN standards, including weather tightness, performance, strength, operational longevity and ease of use. Certified systems are regularly inspected at the manufacturing site to ensure consistent production quality.

3 https://knowledge.bsigroup.com/products/enhanced-security-performance-requirements-for-doorsets-and-
windows-in-the-uk-doorsets-and-windows-intended-to-offer-a-level-of-security-suitable-for-dwellings-and-other-buildings-exposed-to-comparable-risk-1
4 https://www.gov.uk/government/publications/security-in-dwellings-approved-document-q

Having an in-depth understanding of the various tests covered so far enables specifiers to determine precisely what performance requirements they should be requesting and allows manufacturers to select appropriate combinations of materials to meet those performance demands.

This is illustrated by the table below that shows how different combinations of glass thickness as well as the number and thickness of the laminated glass layers can achieve improved glazing ratings for laminated security rated glass.

Laminated security rated glass, referred to as P*A glass, consists of two panes of standard float glass bonded together with a polyvinyl butyral (PVB) film in the middle. The break pattern of the glass combined with the PVB interlayer improves the resistance against penetrative entry slowing the perpetrator down from gaining entry.

The contribution of the frame in glass doors should not be overlooked. A strong, well-designed frame constructed from robust materials can significantly enhance the overall impact resistance of the door and improve its security performance. Choosing frame materials such as aluminium rather than plastic frames that can degrade through expansion and contraction will add to the long term performance of the frame and the glass door. The drive for slimmer frames to achieve a more refined aesthetic must be balanced with frame designs and material choices that do not prioritise visual appeal at the expense of the doorset’s functional integrity.

Material choices also play a part in the long term performance of glass doors. New materials based around nanotechnology such as carbon nanotubes can be incorporated into glass to repair microscopic flaws and create stronger impact-resistant glass 5 . The impact of emerging glass technologies, such as smart switchable glazing that can block or admit light at the flick of a switch, must also be evaluated to determine how they affect impact resistance.

The rigorous testing regimes set out in the standards we have discussed provide manufacturers with the opportunity to evaluate new product innovations, while giving specifiers confidence in the performance claims made for these new products.

5 https://repository.rice.edu/items/c5f4186f-ed92-4763-aea5-a706f6bb8b2f

Solarlux is a leading manufacturer of premium glass solutions and have a wealth of experience in supplying stunning sliding doors and bi-fold doors manufactured to the highest standards.

Justin Spires, technical lead at Solarlux comments: “Solarlux has long stood for exceptional quality in the design, production and installation of bespoke glazing solutions. Our glass doors are developed in-house and manufactured in our own production facilities in Germany. They are rigorously tested to ensure specifiers can be confident they will deliver the required performance and meet the demanding aesthetic expectations of our customers.”

If you would like to find out more about our glass doors, please contact us and we will be happy to help offer specification guidance or a CPD. You can also visit our website to download brochures and technical guides and check out all of our products and see them in action in our product galleries.