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CROSS Safety Report

Behaviour of Phase Change Materials in fire when incorporated in linings in buildings

Report ID: 698 Published: 24 May 2023 Region: CROSS-UK


Modifications are being made to the composition of some plasterboards by incorporating Phase Change Materials (PCMs). Such materials may alter the fire performance of the plasterboards. 

Key Learning Outcomes

For contractors:

  • Make certain that there are no unapproved substitutions of plasterboard types  

For fire engineers:

  • When phase change plasterboards are being considered, be aware of any performance constraints 

  • Apply caution when balancing fire related properties against energy saving requirements 

  • Any combustible products within concealed areas should be considered as a part of the fire load calculations if they are not encapsulated, and the potential impact of phase change on the spread of the flame should be checked

For structural engineers:

  • When specifying plasterboard for passive fire resistance of structural components, be sure to understand the properties of the type of product being specified 

For Fire and Rescue:

  • PCMs may behave differently in fire compared to common building products. They may be concealed within building systems (internally or externally) potentially creating unexpected fire development

Full Report

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The Full Report below has been submitted to CROSS and describes the reporter’s experience. The text has been edited for clarity and to ensure anonymity and confidentiality by removing any identifiable details. If you would like to know more about our secure reporting process or submit a report yourself, please visit the reporting to CROSS-UK page.


A reporter raised a concern regarding the perception and use of products that incorporate PCMs.

PCMs can be incorporated in building materials or products with the aim of increasing the energy performance of the building in which they are installed. This happens because of the improved thermal mass storage capacity these products have, resulting from the melting and resolidification of these materials at room temperatures. The increased thermal mass can reduce temperature fluctuations and energy costs.

However, when organic, many of these materials are usually paraffin waxes or fatty acids, which are flammable. If used as internal or external linings, and exposed to an intense thermal environment such as a compartment or external fire, they have the potential to contribute to the fire load, promote flame spread, or affect a separating element’s time to failure, severely altering the fire dynamics. There is still limited understanding in quantitative terms about their behaviour in real fires.

many of these materials are usually paraffin waxes or fatty acids, which are flammable

Claims about the flammability, or alleged lack thereof, of PCMs have been made in literature outside fire safety, but they have been found to not be based on proper and thorough fire assessments of the materials.

Additionally, the available standardised testing methods are intended to consistently classify the performance of materials/products/systems, and by their nature cannot cater for providing a detailed characterisation of the individual materials that a product may be comprised of, or how each of these affects the behaviour of the product in a fire. This means that results from standard fire test methods cannot be used to balance fire safety with energy efficiency for a holistic assessment of the building’s performance. This is even more important for products whose composition is complex, sophisticated, and only known to their developers (which is usually the case with a novel material or product). This latter case will require bespoke testing methodologies to initially understand, and then quantify their expected performance.

The reporter suggests that to employ the sustainability benefits of PCMs while using them in a safe manner, a risk based approach that takes account of realistic fire behaviour will be necessary. Using information such as the critical heat flux, the heat release per unit area and the mass loss rate will allow the contribution to a fire to be quantified and for any fire risk associated with these materials to be mitigated and balanced.


Expert Panel Comments

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Expert Panels comment on the reports we receive. They use their experience to help you understand what can be learned from the reports. If you would like to know more, please visit the CROSS-UK Expert Panels page.

This report relates to the potential risk arising from the use of materials that, to the knowledge of the Panel, have not yet been used in the construction of buildings, but may be used as efforts are made to achieve net zero.  

Should PCMs be used, these areas of concern have been identified: 

  • the amount of fire load these types of products would add to a building system 

  • the impact of heat on the state of the product 

  • the potential impact on fire spread and the applicability of current standards to control the risk 

  • ensuring those who will be expected to try and safely extinguish any fire have the knowledge they need to be able to do this 

Fire load and reaction to fire 

It is not known if any products containing PCMs have been tested for their reaction to fire, as individual products or as part of a system. The Panel identified BS PD 6688-1-2:2007 Annex A and Eurocode 1991-1-2 Annex E as relevant standards to be applied.

The impact of heat on the state of the product is also important. The extent of the impact would depend on the level of containment and the location of the material in the construction. For example, if the product is fully encapsulated in a non-loadbearing construction that is not by passing a compartment line, the phase change will not considerably impact the fire performance. But, if the product is forming a part of a non-loadbearing arrangement passing through a compartment, such phase change could lead to the formation of a cavity which then would lead to the excessive spread of flame. 

The extent of the impact would depend on the level of containment and the location of the material in the construction

It is important that reaction to fire tests be carried out by people who are independent of the suppliers of these systems. There are many examples of suppliers of new innovative products carrying out assessments of performance, which are intended to convince people to purchase their product, without addressing the risk properly.


The National Fire Chiefs Council has published a position statement, emphasising their concerns about the development of new materials and approaches overtaking the current (under revision) legislative framework.

It is unlikely that PCM used within a system would be apparent to firefighters dealing with an incident. Where such materials are used, if they create the potential for supporting hidden fire spread or adding significantly to fire loading, a means of bringing this to the attention of attending firefighters should be created. Construction techniques and materials are evolving so quickly that it can be difficult to keep up, not only in understanding their fire performance but also ensuring those that will be expected to try and safely extinguish any fire have the knowledge they need to be able to do that.

Relevant research

This topic was the subject of PhD research carried out at the University of Edinburgh.

Regulatory guidance

This report highlights a wider issue in relation to Approved Document B (ADB) guidance on Part B2 of Schedule 1 to the Building Regulations, in that the three sub-provisions (1a - flame spread over surfaces, 1b(i) - the rate of heat release and 1b(ii) - growth rate) have effectively been condensed into linings (i.e. the outermost surface) having to be a BS 476 or 13501-1 rating. This could be seen as wholly inadequate for layered elements, including PCMs, and aluminium composite material (ACM), where the dangerous layer is shielded by a surface layer that can pass the test. For ADB, a PCM (or indeed Category 3 ACM) could achieve Class 0 but could also result in rapid flame spread over the surface in a building fire, as opposed to a test fire, as well as a high heat release rate and a high growth rate (i.e. failing to comply with Part B2).

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