The dangers of the hot motor test in BS 8524-1

It’s 400°C and your fire curtain motor is still working…

Is this a good thing, or is it actually dangerous?

“BS 8524 is a more rigorous standard with extra tests specific to fire curtains…”

One is the hot motor test.

BS 8524-1 requires fire curtains to conduct a hot motor test, where the motor must operate 12 times over 30 minutes with the furnace temperature at 400°C ± 20°C.

In theory this could be seen as a good test, as it potentially shows the robustness of the curtain’s control mechanism, even under extreme conditions. However, a fire curtain should never be operable if there are temperatures of 400°C on one side, as this would pose a severe-to-fatal risk to the operator and could allow the fire to pass beyond the designated compartmentation barrier and thus endanger the whole building.

It could be argued that the hot motor test is for applications where the motor is high above the operator, for example in a ceiling void. In this situation, if there were a fire or hot smoke and gases in the void and not lower down, and if you wanted to operate the fire curtain, you have a rare combination where a hot motor use may be applicable. A lot of ‘ifs’.

However, as well as the incidence rate of this combination being very rare, who is going to stop the curtain opening above the safe temperature limit so as to prevent the fire spreading? If it is 400°C up where the motor is, and 20°C down where the operator is, it stands to reason there is a temperature gradient in-between.

What is the safe amount to open the curtain to? Who is going to know this, let alone do it when escaping from a fire?

Additionally, it is questionable if the test genuinely reflects real life anyway; what happens to the Control Panel at 400°C? The Control Panel is typically installed at high level with the motor. It is unlikely the Control Panel would work and tell the motor to operate at temperatures over 100°C, let alone approaching any temperature that would affect a motor. The components in the Control Panel (plastic contacts, printed circuit board, and other plastics) would melt and certainly not work long before a motor became a problem.

The ASFP point out in ‘Advisory Note – ASFP position on Performance Smoke Seals in Active Fire Curtains Document’ that no one should even be close to the fire curtain at these temperatures. “Smoke detectors will alert occupants to the fire before flash-over has occurred. The curtain will deploy, and occupants can make their escape… the limiting factor in determining the occupation time is the length of time before the radiation through the curtain will cause the escape route conditions to become untenable.”1

Hot water burns us at around 70°C. It scalds us at 100°C. The emergency services would not open a fire curtain with the temperature at even half of the 400°C as it would exceed the limits to which firefighters are trained; see “Characterizing a Firefighter’s Immediate Thermal Environment in Live-Fire Training Scenarios” which states “severe training conditions generally [exposed firefighters to] temperatures between 150°C and 200°C”2

To justify this test being of potential value, data is required to show how often the combinations occur where the capability to open a fire curtain when the motor is at 400°C would be a potential benefit, and control measures are required including easy-to-use instructions by the user in a fire situation, so they don’t open the fire curtain too far and thus endanger the building further. A failsafe back-up to stop the fire spreading is also required in the event of user-error. Also required is a Control Panel and components that work in the temperatures required of the motor e.g. 400°C.

Otherwise, this is a dangerous capability (as well as not true to real life), and the motors should be designed so they do not work at elevated temperatures so as to protect people and property when in close proximity to dangerous temperatures.

The capability for an untrained person to operate the motor at 400° in the overwhelming majority of circumstances is dangerous. Whilst this test may have the best of intentions, on the balance of risk that it poses in its current format versus any benefit it may provide in very rare circumstances, it should be removed.

Note. Even if this test were a good thing and if it could have benefits somewhere, the expansion of the bottom bar at 400°C is untested and it is very questionable whether the motor would be capable of moving the curtain if the bottom bar had expanded and jammed in the guides.

The above is an extract from the Adexon white paper, A technical comparison of BS EN 16034 and BS 85242.

References

1 ASFP (2021) ASFP advisory note.pdf, Zoho WorkDrive. Available at: https://workdrive.zohopublic.eu/file/a7yip4e4df488d7d44a76a28d2d556e110def.

2 Willi, J.M., Horn, G.P. and Madrzykowski, D. (2016) Characterizing a firefighter’s immediate thermal environment in live-fire training scenarios – fire technology, SpringerLink. Available at: https://link.springer.com/article/10.1007/s10694-015-0555-1 (Accessed: 30 June 2023).