Last month, we released a video demonstrating the effectiveness of our insulated fire door (Rhino-FDi90HL) against a standard integrity-only fire door. The result was compelling footage which highlighted the superior strength and performance of the Rhino door, and its potential industry-wide applications. 

To delve deeper into the door design itself and our motivations for producing the video, we speak to Stuart Lawrence, Group Managing Director of Rhino Engineering Group, to learn more about what sets the door apart from the rest.

How long has Rhino Doors been working on the Rhino-FDi90HL fire door? 

We actually started this project in late 2019, and finally completed the last test in July 2022, so a little over two and a half years. This is considerably longer than we would normally expect a development project to take – however, there were a number of technical challenges to overcome, which meant that some of the early tests were repeated several times in order to establish an effective design. 

The development period was also extended due to the availability of fire test facilities, a result of increased fire testing within the industry over the past two to three years.

What were the main challenges encountered during the development project? 

The principal challenge associated with designing a combined integrity and insulation door centres around the differential expansion created between the hot face (furnace, or fire side) of the leaf and the cold face. The more you increase the insulation rating within the core of the leaf, the greater the temperature difference you achieve between the two leaf faces – and, of course, this is precisely what you want in an insulation rated door. 

However, the greater this differential in temperature, the greater the differences will be in thermal expansion between the two faces, and this results in stresses within the door leaf that can be high enough to significantly distort the leaf, ultimately even resulting in an integrity failure. 

It therefore becomes a balancing act to ensure that there is sufficient insulation within the core of the leaf to keep the temperature rise on the cold face within the limits prescribed by the standard. Too much insulation and the door may even fail on integrity (flame transfer from the fire/furnace side to the cold face side) due to the stresses caused by differential expansion before insulation limits are reached. 

There is also a danger of trying to compensate for differential expansion by increasing the stiffness of the leaf core. However, this only increases weight and can result in increased heat transfer through the core of the leaf. 

Achieving the correct balance, particularly on doors rated for more than 30 minutes (and ours is rated at 90 minutes) is especially challenging and can require several iterations of design and testing to achieve the optimal configuration.

What key elements set it apart from comparable doors produced by other manufacturers? 

Our primary objective when we embarked on this development project was to produce a door with a combined integrity and insulation rating of at least 90 minutes, whilst maintaining the appearance of a commercial steel door which possesses aesthetic appeal to architects and other specifiers. 

Commercial steel doors are generally aesthetically appealing, but tend to have integrity ratings only, albeit up to 4 hours. Combined integrity and insulation doors are routinely used in other settings – for example, within the oil and gas industry – however, their appearance is typically more industrial and heavily engineered in order to achieve integrity and insulation ratings of up to 2 hours. Usually, however, this is not a problem due to the industrial setting. 

What sets our door apart from the competition is that it is a high-performance integrity and insulation door, rated at 90 minutes, which also maintains the appearance of a more conventional commercial steel (integrity only) fire door.

Can you explain the difference between insulation and integrity ratings? 

The difference between insulation and integrity ratings is something that we covered in our recent ‘Ask the Experts’ series, however it is very important to understand and hence worth reiterating here. 

Under the EN 1634-1 standard that Rhino typically uses for fire door testing, successfully tested doors are assigned a series of letters and then a number, where: 

• E denotes that the door is integrity rated. 
• I denotes that the door is insulation rated. 
• The number denotes that time in minutes that the door is rated for.

For example, an EI120 door is one with both integrity and insulation ratings for up to 120 minutes, or 2 hours. An E240 door has an integrity rating only for 240 minutes, or 4 hours. Note that insulated doors must maintain their integrity for the same period of time as the insulation – i.e. it is not possible to have an insulation-only rated door. 

As a further refinement, EN 1634-1 doors that have an insulation rating will sometimes be recorded with a suffix 1 or 2 after the EI element of the code, e.g. EI₂120. This suffix is used to indicate where the thermocouples on the cold face of the leaf are positioned, relative to the frame fixed to the wall. A suffix ‘1’ means that the thermocouples are placed closer to the wall frame, which means they are likely to heat up quicker – therefore a more onerous test.

What was the rationale for producing the demonstration video and what specific challenges were encountered? 

Whilst integrity-only rated fire doors are perfectly adequate at preventing the passage of an actual flame from one side of the door to the other, we wanted to demonstrate that it is still possible for a fire to move from the fire side to the ‘safe’ side, even if the integrity-only rated fire door has not suffered an actual integrity failure. 

This phenomenon occurs due to the very high levels of radiated heat which can be emitted from an integrity-only rated door, and which could cause everyday household objects located on the ‘safe’ side of the door to catch light. 

Of course, in reality it is unlikely that such objects would be located so close to an operable door (certainly not immediately in front of it). However, the point we were trying to make was that demonstrably the heat transmission through an integrity-only rated door can be significant, and this could have consequences for people taking refuge behind the fire door. 

Placing our 90-minute integrity and insulation rated door panel adjacent to the standard integrity-only rated door panel for the demonstration video facilitated a direct comparison between the two door types. It highlights very clearly that, when exposed to the same furnace conditions, the insulated door prevented the onward transmission of the fire, whereas the integrity-only door did not.

Are there particular settings in which the Rhino-FDi90HL might find applications? 

We believe that any setting in which a fire door is installed to provide a safe haven for people (or high-value material assets) in the event of a fire, whilst they await rescue, will clearly benefit from a combined integrity and insulation rated fire door, such as our Rhino-FDi90HL.

You can watch the fire test video here to see the Rhino-FDi90HL fire door’s performance and click here to read more about the door and its industry-leading potential.