In last week’s post I showed how CRC i2® elements had performed during a real fire at the Heilig Harn project in Den Helder in Holland. This time I’ll complete the mini-series on the topic, describing two more projects and the unfortunate incident with a charcoal chimney starter directly on a CRC i2® balcony…
The projects with CRC i2® elements where fire occurred in the construction phase are:
- November 26, 2012: Sydhavnsskolen, Copenhagen (DK)
- September 22, 2016: Heilig Harn, Den Helder (NL) – described in last weeks post
- September 29, 2016: Strandingsmuseet, Thorsminde (DK)
Copenhagen, November 26, 2012
Sydhavnsskolen (The South Harbor School) was close to completion when fire broke out in several different places during the night. The fires spread and ended up destroying a large part of the interior of one floor – and ended up being put out at the newly installed Hi-Con CRC i2® suspended staircase.
Sydhavnsskolen (The South Harbour School) in Copenhagen on fire.
When I inspected the site a few days later it was obvious that we had been very lucky – the firefighters put the fire out just a few meters short of the stair, with only heat, smoke and water having affected the stair.
Consequently the CRC i2® staircase had not been subjected to temperatures above 200-300°C – known because the fire paint on the suspension struts had not expanded. No actual damage was visible.
Underside of CRC i2® staircase and suspension struts covered in sooth after the fire. The soiling from burned material and the water used by the fire services is very apparent. The fire paint on the struts is not expanded indicating temperatures below 2-300°C at the stair.
The regular concrete columns in the building were not so lucky though and these experienced significant spalling, and again as seen at the fire at the Heilig Harn right down to the main reinforcement despite normal cover layer thickness:
Conventional concrete column severely spalled exposing the main reinforcement
After cleaning it became apparent that the heat and water had made the less protected steel parts corrode here and there – not to mention the extensive soiling caused by the combination of burned material and all the water used to quench the fire, and the staircase subsequently had to be thoroughly cleaned and painted, but not otherwise repaired.
You can see the completed project here.
The completed staircase today.
Thorsminde, September 29, 2016
A refurbishment of Strandingsmuseet St. George (The St. George stranding museum) was well underway, and craftsmen were applying torch-on roofing felt onto a section of the roof close to the newly installed CRC i2® façade panels. Some insulation flamed up, but was put out straight away. Or so it was thought. Below an image taken right after the initial small flame-up – a small smudge is visible at the joint between two of the CRC i2® façade panels (in the red circle).
The facade of the “tower” after the initial small flame-up – the only visible indication is the small sooth smudge at the joint (in the red circle)
However, during the night, driven by strong winds made worse by the chimney effect of the high façade, the fire reignited, causing high flames exiting joints and openings in the top panorama room of the “tower” and into the air above.
When the fire was finally put out, I inspected the site for damages to the CRC i2® façade panels or the support brackets holding them.
First, it was determined that most of the heat was contained inside the insulation while it was burning – therefore, heat damage was only visible at the exit points, as in the panorama room at the top of the “tower” shown below.
Exit point of the flames in the panorama room in the “tower” after the fire (l) and close-up of the space between the interior regular concrete wall and the CRC i2® facade panels (r). Charring of a wooden spacer is clearly visible.
It was clear that locally, the flames had caused damage, but only minor superficial indications of this was visible on the inside of the CRC i2® facade panels and brackets.
The most significant I found was a small patch with a light-coloured slightly powdery surface ½ a mm deep indicating temperatures of no more than app. 200°C (enough to slowly decompose the cement based hydrates at the surface but not enough to result in deeper damage).
Inner side of CRC i2® façade panels (l) with some light patches with very superficial heat damage and a melted plastic spacer on a bracket at the top connection of a panel at the roof. No damage visible on the bracket.
The conclusion was that nothing serious had happened to the façade panels, and that repairs except for cleaning was not necessary. It was however necessary to remove several panels in order to replace the burnt-out insulation.
The inauguration of the completed museum showing the up to 15 m high CRC i2® façade panels.
More Images of the completed museum are available at our webpage.
Finally, a short (kind of funny) story:
November 2012, “The Copenhagen grill incident”
In November 2012, I got a call from a building manager with a problem: one of his tenants had placed a charcoal chimney starter directly on a CRC i2® balcony surface.
The charcoal temperature inside a chimney starter is in the range of 400-1000°C, depending on many factors (and who you ask), but it is hot enough to reduce iron (this is why chimney starters rust when left outdoors after use), but not hot enough to melt it. Airflow at the base also reduces temperature, so an educated guess is, that the CRC i2®surface was exposed to app. 250-400°C, but for some time – it can take up to an hour before the charcoals are ready.
The result of exposure to the heat of a charcoal chimney starter
The damage was only 1-2 mm deep and consequently of only aesthetic importance, but the area will never look like the rest of the balcony. No explosive spalling occurred thanks to the CRC i2® – otherwise a potentially nasty accident involving flying red-hot charcoal!
What did we learn?
Summarizing the projects above, what can we learn, since the CRC i2® elements actually had not sustained any serious damage? Well, at least the following:
- Significant damage (and cost) because of fire is not necessarily caused by heat – it can (and commonly is) just as much from all the very dirty water and necessary rough actions taken by the firefighters in order to put the fire out. So using building components that are easy to clean is important.
- Regular concrete also experiences spalling (seen also in the last post – even at normal “low” grade concrete. So the question in Bendt’s post Fire resistance – is it a problem for UHPC? could just as easily be stated for regular concrete – the difference being, that for CRC i2®, testing is required and has been made to verify that this UHPC type behaves well in fire conditions.
- Robustness of elements and assembly methods allowing easy repair or replacement in case of serious damage is very important to keep down the cost and time of bringing construction back on track.
- Fires may occur where you least expect it – no one had foreseen that insulation could burn in the case of the Museum in Thorsminde, or that someone would light a fire directly on a balcony – but it did in fact occur. So using building components with good built-in fire properties can mean the difference between serious damage and harm to property and people, and minor and easily repairable damage.
This concludes this miniseries on the fire properties of CRC i2®, however as always, your comments and questions would be appreciated, and if relevant we will add more posts on the subject in the future.
Tommy Bæk Hansen
Group Product Development Manager
Read about Tommy’s 20 years of experience with UHPC right here