Structural Fire Protection For Commercial Buildings 2024 review

Present day building activities have a bewildering array of flexibility, particularly in design, construction, and aesthetic opportunities. In most cases commercial buildings use a combination of concrete and steel as the main construction element, both materials require fireproofing to maintain structural integrity, reason being a typical commercial fire can generate temperatures more than 1000°C with a typical heat flux of 120 -150kW/m². Temperature resistance for these materials is relatively low, approximately 320ºC for concrete and 550-620ºC for steel. Once these temperatures are reached or exceeded, both elements will either deflect or collapse.

Design authorities divide fireproofing materials into two categories, friable, semi-hard / durable. Friable products are for interior use, to protect the underside of concrete floor slabs, and structural steel hidden under suspended ceilings or false walls.  Semi-hard and durable materials can be exposed internally and externally, however in many cases they may require supplemental paint coatings for water, UV resistance, and or for architectural reasons.

When commercial buildings are exposed to fire, damage invariably is extensive and costly in financial terms, and in some cases human injury or loss. In most parts of the world authorities require certain construction materials to have a fire-resistant rating to withstand the elements of a commercial fire for a required period. Resistance for a particular situation is directly related to the anticipated fire load, occupancy of the building, height, and area. The basic aim is life protection, giving people time to evacuate the building and to protect or minimize damage to the building.

The design philosophy behind the development of fireproofing materials was to limit heat absorption and maintain a temperature within defined limits so that emergency fire fighting practices can be put into effect. Products must fulfil their fire protection role by limiting the temperature of a structure below the maximum permitted temperature over a specific period in the stated fire condition. More importantly materials must not fail suddenly at the end of this specified period but continue to offer a predicable measure of protection beyond this point.

Other design considerations:

• System integrity, remain in place during a fire and be able to withstand both thermal shock and by impingement of water from fire hoses or monitors.
  • Be none-corrosive to the substrate.
• Must not become a hazard, by spalling, spreading flame or producing toxic fumes.
  • Easily applied in various environmental conditions without causing undue mess, or interference with adjacent operations and plant.
  • Durable and easily repaired.
• Be cost effective for the risk involved.
• For existing installations be compatible with a wide range of paint systems including lead-based paints where removal may not be practicable for environmental or safety consideration.
• Protection of lift well doors and essential services such as water pump supports, deluge systems, power cables and piping require special consideration as they all contribute to safety of life.

Structural steel members are often highly stressed to permit structural requirements to be met more efficiently with the minimum weight of steel. However, strength decreases significantly (Fig 1) as temperature increases. Fire resistance tests throughout the world have shown members loaded to normal design limits collapse when temperatures in the order of 550º-620ºC are reached. In the case of unprotected steel, collapse can occur after only 10-15 minutes. This brief period would have disastrous consequences for human life as well as structural considerations.

Regarding concrete, it can spall, explode, and collapse in a very short period, particularly if temperatures rise above 300ºC. Structural failure is invariably the result even if the structure appears intact, apart from any physical damage; it has been known to lose up to 50% of its strength. Spalling has the capacity to expose reinforcing steel which may result in catastrophic failure, as in the case of the US World Trade Centre, re 9/11. Chemical changes occur which can lead to further spalling days after the fire incident, as water is reabsorbed back into the concrete substrate.

The choice of aggregate used has a bearing on performance as some are more suitable than others, for example, river pebbles should never be used as they contain water and when heat stressed, explode. To put concrete into some perspective, it is mandatory in Australia, USA, and the EU that the underside of all concrete floor slabs be fire protected. Fire testing is twofold; the temperature at the interface between the fireproofing and the concrete should not exceed 380°C, and the temperature of the reinforcing steel shall not exceed 250°C.

Materials Available for Selection 🙁 not all listed)

INTERNAL USE                                                                     THICKNESS RANGE

Spray applied Vermiculite / Cement mixtures                                    10-50mm.

Rigid vermiculite board                                                                       18-75mm

Spray applied gypsum/plaster mixtures                                             10-50mm.

Spray applied mineral fibre/cement mixtures                                    10-50mm.

Mineral fibre board                                                                              6-12mm

Calcium silicate board                                                                         12-25mm

Epoxy intumescent paint                                                                    2-20mm

Acrylic intumescent paint                                                                    300-750 microns

Chlorinated rubber paint                                                                     300 -500 microns

EXTERIOR USE                                                                    THICKNESS RANGE

Cementitious vermiculite mixtures                                                     8-100mm

Epoxy intumescent paint                                                                    5-20mm

Supplementary topcoats

Epoxy/Polyurethane                                                                           75-100microns.

Polysiloxane                                                                                        75-100microns

Chlorinated rubber / acrylic waterproofing membrane                      300-500microns

Selection of product type is related to the required fire rating in terms of time, from 30 minutes to four hours.

Building regulations in Australia, USA and the EU are all very similar. Australian Standard AS1530 has a slightly lower failure criteria of 540°C, whereas the UK/ EU at 550°C and USA at 590° C. Regulations in Australia permit the acceptance of similar tests, however this is only accepting that the time temperature curve in the test furnace is the same, but it is conditional that the failure criteria specified is that of AS1530 at 540° C.

Performance of steel is considered in terms of three main aspects: –

• Thermal – relates to thermal properties of the fire protection material.
• Mechanical – the relationship between steel temperature and the load bearing capacity in fire.
• Stickability – the ability of the fire protection material to remain in place as the steel member deflects throughout the fire test.

By their very nature, standard fire tests were designed to act as a benchmark to determine in a consistent manner, the performance of products and systems to a particular fire condition. What these standard tests “cannot do “is to determine the performance of (1. Wind turbulence and (2. Thermal shock caused by accelerated temperatures, together with water from fire hoses and/or sprinkler systems. It is worth noting both conditions can occur during a fire, heat flux generated is difficult to measure accurately. Fire tests are based on time/temperature curves and do not consider heat flux, whilst not necessarily reflecting a real fire they do nevertheless provide a reproducible method by which the performance of fire protected structures may be evaluated.

Insulation thicknesses are either based on the H/Pa factor, (heated perimeter / cross sectional area) or the area to mass ratio of steel. Material suppliers are required to conduct a series of independent tests 9 to 12 so that charts or graphs can be drawn up for a whole range of steel sizes. Single or small-scale tests are not used unless they are accompanied by full scale tests. Manufacturer’s in-house fire tests are not acceptable unless they are substantiated and witnessed by an authorizing independent authority.

Tests relate to load bearing members and are based on varying steel sections, conducted for one, two, and four hours or similar.  Heat uptake or absorption is slower as steel thickness increases; therefore, thinner insulation is required conversely with lighter sections thicker insulation is needed. Bracing components receive a nominal H/Pa value for basic cover and protection.

What the tests give you is a regression formula (a window) if you like, on varying steel sections which defines interpolation limits for calculating the required insulation thickness. Strict limits are applied to the use of this regression formula; no material thicknesses are acceptable if they fall outside the test window. Where no regression formula is available, a single test prototype must be conducted for the steel member involved.

There is one important point to be emphasized, charts or graphs related to any given material thickness can only be derived through INTERPOLATION, (mathematics: transitive verb to estimate the value of a mathematical function that lies between known values, often by means of a graph) and not extrapolation (transitive verb to estimate a value that falls outside a range of known values, e.g. by extending a curve on a graph). Materials should never be offered or accepted via extrapolation without the minimum 9-12 tests being conducted.

There are legal implications involved with commercial fire protection, any person in the supply chain whether they are the specifier, construction manager, material supplier, or installer have a shared responsibility for its performance or usefulness in the event of an untoward fire. For example, in the event of a fire where deficient installation has been found, the supplier and the construction manager can no longer claim the responsibly was not theirs on the basis they had no control over the installation, they are likely to be found culpable as with the deficient installing contractor. There is a principle called “Tacit Approval” implied but not spoken, therefore it becomes a shared responsibility if anything untoward occurs, this applies to contract specifications, possible doubt to total conformance or perceived performance. The concept of voluntary duty of care is no longer enough, it is now a legal obligation.

Most countries have building regulations which encompass health and safety rules (fire safety). Building owners require all the relevant information regarding the fire prevention measures taken to make an effective risk assessment, particularly regarding those who built it, the intendant occupiers, and those who are to maintain the building.

For an individual or corporation to ignore these issues would demonstrate a lack of responsibility, furthermore by signing off on an unproven specification or not providing all the relevant information, would expose those involved to potential litigation or criminal charges in the event of a fire and or the loss of human life. Proven performance with independent test data is the only safe and secure basis for selection.

Recognized testing laboratories include: (not all listed)

• Building research of New Zealand
• Fire insurance research and testing organization, UK.
• National Bureau of Standards, USA
• Underwriters Laboratory, USA
• Underwriters’ laboratory, Canada
• National Research Council Canada
• CSIRO Australia
• Building Research Station Australia
• Warrington Research UK

Carbon steel rapidly loses strength when its temperature increases and will deflect or collapse when temperatures of approximately 550°C and above are reached.