Critical services require stringent controls of the environment and temperatures through which they travel. The system designers are often challenged by the installation of systems that are unable to adhere to the ‘Critical Services’ temperature required by the Code. A prime example is where the installer is allowed (or instructed) to adopt a duct fire protection system to encase critical services, however the duct system does not meet the minimum requirements of AS 1530.4-2014, Section 12, Critical Services (for the purposes of this article, referred to simply as “Section 12”). The challenge for designers is understanding the intricacies of AS 1530.4-2014 in its entirety, to be able to meet the standard set by the Code, in order to maintain standards of life safety required in Australia, all whilst coming within the financial constraints of the project.
Critical services enclosures are engineered to maintain temperatures to a very low threshold – so much so that after a 4-hour fire test, the recorded temperature of a fibre optic cable within such an enclosure, must not be allowed to rise above 66°C. In a similar vein, a 25mm copper pipe insulated with 9mm K-Flex should not rise above 43°C.
What are critical services?
Critical Services as defined in Section 12, include:
- Copper conductors and busways;
- Optical fibre cables;
- Data cables;
- Communication systems;
- Fire detection and alarm wiring;
- Hydrant systems; and
- Emergency control systems.
Section 12 may also apply to enclosures to hazardous services such as:
- Pipes carrying flammable fluids;
- Medical gas lines; and
- Enclosed systems (ducts /shafts).
Figure 1 – Critical services safeguarded by Vermitex® TH.
The safeguarding of electrical, data and communication cables, conductor bus bars and refrigerant pipes from direct fire ensures that critical services being supplied by these enclosed elements, will continue to operate because the maximum operating temperatures in a fire emergency will be contained to acceptable levels. Innovative enclosure technologies also serve the function of containing toxic smoke produced within the enclosure (most electrical conductors are sheathed in polymer, synthetic rubber or in special cases, encapsulated mineral insulated materials). Polymer materials emit toxic fumes which can be cause for concern during the evacuation of occupants in an emergency
Figure 1 shows a recent application where the bottommost (two) cable trays, supporting substation HV redundant cables in a tunnel project, were encased in an innovative 4-hour fire rated spray applied system.
The mechanically spray applied fire protective coatings can be sprayed directly over the cables, but to achieve the best performance it is recommended that the spray be applied over a 3-D mesh which should be formed into a box-enclosure space 50mm away from the cable tray.
Unless the enclosure is forced ventilated, it is important to consult with the electrical engineer to verify whether the cables require ‘de-rating’ given the excellent insulation performance of these mechanically spray applied coatings.
With the imminent introduction and adoption of NCC 2022, a number of projects have been inspected where electrical and refrigerant pipe critical services have been found to be enclosed in air handling fire protection systems instead of critical services enclosure systems. In Code terms, this means the critical services are enclosed in systems which comply with AS 1530.4-2014, Section 9, Air Ducts (for the purposes of this article, referred to simply as “Section 9”), instead of Section 12.
Why is the comparison between Section 9 and Section 12 important and relevant?
An air duct enclosure, tested to the requirements of Section 9 is capable of maintaining an internal temperature within the duct, to an average of 140°C with a potential maximum temperature of 180°C + ambient temperature.
Section 9 is not designed to fire test systems to maintain very low temperatures within the enclosure. When dealing with air handling ductwork, insulation failure is set to occur when the average of the unexposed face of the test specimen (as measured by the thermocouples specified in sub-section 126.96.36.199), exceeds the initial temperature by more than 140°C, or the temperature at any location on the unexposed face of the test specimen exceeds the initial temperature by more than 180°C.
These temperatures are much too high to satisfy the standards imposed by Section 12 and set out in Table 12.6.
Figure 2 – Extract of AS1530.4-2014, Section 12 Critical Services, Table 12.6.
Section 12, and a number of manufacturers of refrigerant pipes and electrical cables, indicates that the critical temperature of any such pipes and cables should be maintained below 75°C.
Accordingly, when compliance is mandated for critical services (including hazardous ones such as pipes carrying flammable liquids and medical gas lines), Section 12 should not be mistakenly overlooked in favour of the lesser performing protective system of Section 9 (which is appropriate for air ducts but not critical services).
The real risk of confusing Section 9 and Section 12 is that the mistake can be made at any point of the process – whether it be in installation, design, testing etc. For example, installing a critical services enclosure which complies with Section 9 but not Section 12 means that the final occupants/ users of a building could wind up in a situation where the structure’s emergency power system fails before its non-critical services do. Similarly, testing enclosure products against Section 9 will only prove the product’s suitability for use in air duct enclosures – not critical services. Ultimately, the distinction between Section 9 and Section 12 must be made at the testing stage, and then carried through to the design and build/ install stages.
Methods of testing are therefore vital to ensure the correct application of Section 9 or Section 12 as appropriate. For application to critical services enclosures, critical test data should be taken from within the fire rated enclosure (externally exposed to fire) so that the hottest exposure data is considered.
Using data taken from thermocouples on the unexposed face of a wall, cooled by ambient air, would assist if one was assessing a ‘zone to zone’ compartmentalization, however it does not provide the best data to maintain critical services at the low temperatures required by Section 12.
The importance of product testing cannot be overestimated. In particular, one should meticulously analyse:
- if the accredited testing laboratory is NATA accredited in testing to the required standard;
- how stacked or single enclosures are tested (fire direction – internal/ external);
- whether cables (optical, copper etc.) were correctly rated and have been tested to AS 1530.4-2014; and
- if the thermocouples were internally located, or in a cooler outer position.
For a critical services enclosure to comply with Section 12, the thermocouples would need to be placed on the cables within the enclosure and over the line of the furnace chamber.
The results above confirm that protection of critical services, to a Section 12 standard, is certainly achievable. The issue is therefore ensuring, at a specification and installation level, that the correct standard is applied in order to preserve life in the event of an emergency.
Examples of large-scale projects incorporating critical services
Critical services enclosures may be installed in any number of projects including:
- multi-use arenas;
- road tunnels; and
- commercial buildings,
in order to safeguard any number of critical services as follows:
- main and redundant substation bus bars;
- main HV & LV cabling; and
- fibre optic cabling.
Contractors are typically intimately involved from the design stage of the above types of projects, all the way to delivery of the complete fire protection solution.
It is concerning to think that the confusion between Section 9 and Section 12 could be leading to critical services systems in large infrastructure projects being protected by inferior fire protection systems which were possibly originally tested to protect ducts or other services, but certainly not critical services. A greater attention needs to be drawn to the distinction between the two sections so that the correct design decision is made at the relevant time i.e., at project design and inception stages.
If disaster strikes, no one in the project chain wants to be liable for negligence or breach of a duty of care. The consequences of such an emergency could be catastrophic for the occupants and users of the building, and the legal ramifications for negligent contractors would be severe. Diligent manufacturers and contractors provide solutions that are specifically engineered with a safer built and compliant environment in mind. The result is a fire insulation standard for critical services, which ensures that materials within protected spaces remain insulated and perform to expectation.
 AS1530.4-2014, Section 9 Air Ducts, sub-section 2.13.3.
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