Fire compartmentation

Readers may recall in Issue 14 of Gulf Fire (April 2019 edition), an article that featured the development of international fire codes and standards. In a similar fashion the use and development of compartmentation can be traced back historically to significant fire events.

The Great Fire of London on 2nd September 1666 led to the first set of Building Regulations in the UK with the introduction of the Act for Rebuilding the City of London, 1667. This act identified the concept of passive fire protection and the use of non-combustible building materials to limit the growth and spread of fire. Some of the design issues addressed in these regulations included:

• Walls of all new buildings were to be of brick and stone;
• Main streets were to be wide enough to prevent fire spread;
• The number of existing narrow alleys were to be reduced.

Fire safety refers to precautions that are taken to prevent or reduce the likelihood of a fire that may result in death, injury, or property damage, alert those in a building to the presence of a fire, enable those threatened by fire to evacuate from affected areas, or to reduce the damage caused by a fire. Fire safety measures include those that are planned during the design and construction of a building or implemented in structures that are already standing, and those that are taught to occupants of the building.

Every new building should have a fire strategy to support the approvals process and should contain information relating to the buildings fire protection systems and management plans. As a minimum the strategy should include details of:

• Occupancy type
• Construction type
• Travels distances – to exits and/or places of safety
• Exits – number and location
• Time of escape
• Management arrangements

Further detail within the fire strategy should detail the two key aspects that are limiting the development and spread of any fires that have started, and the provision of adequate means of escape and other safeguards for the occupants of the building. Limiting the development and spread of fire alone has many aspects. It embraces steps to secure proper subdivision of large buildings by walls and floors of adequate fire resistance. It has to take into account the design of load-bearing members to provide this resistance to the effects of fire, and measures whereby the access for civil defence operational fire crews is facilitated. It includes steps to minimize the risk of the fire spread of fire from one building or part of a building to another, whether they be connected or facing one another across a street or open space. Such measures may be termed passive fire protection and the internal separation fire compartmentation.

Compartmentation is often a key component of the fire safety design of a building and in essence aims to divide large spaces within a building into smaller, more manageable ones should a fire occur. Fire compartmentation can also be used in order to create a safe, protected means of escape for the building occupants in the event of a fire. Generally, these fire compartments are separated from each other by compartment walls and compartment floors made of a fire-resisting construction which acts as a barrier to the spread of fire and smoke for a specific period of time.

Passive Fire Protection (PFP) is an integral component of structural fire protection and fire safety in a building. PFP attempts to contain fires or slow the spread, through use of fire-resistant walls, floors, and doors (amongst other examples).

Compartmentation – Historical Development

Following the end of the second world war a series of reports were published under the title of Post War Building Studies in the United Kingdom. This guidance owed its origin to a desire expressed by professional and other institutions connected with the building and civil engineering industries to assist and support the Ministry of Works in regard to post-war plans. Post War Building Studies No. 20 Fire Grading of Buildings Part 1 – General Principles and Structural Precautions introduced some key concepts that formed benchmarks within fire safety designs including:

• Defining fire hazard when assessing the fire safety requirements for a building;
• Grading of a building occupancy considering the fire load, low, medium or high;
• Subdivision of buildings based on height, floor area and cubic capacity;
• The type of materials used in construction (combustibility) based on the graded type of a building;
• Assessing and defining requirements for openings in fire rated internal walls and floors.

Post War Building Studies No. 29 Part III – Personal Safety further analysed the fire protection requirements in buildings to safeguard the means of escape based on additional considerations and specified the minimum fire resistance requirements having fully considered the following:

• Occupancy characteristics based on the type of building use;
• Subdivision of the building according to the population characteristics;
• Subdivision of the building according to its use (Purpose Group).

The development of the Post War Building Studies included international input and guidance from organisations such as the National Fire Protection Association (NFPA) and remains a good basis for understanding key fire safety concepts particularly in relation to building construction and fire compartmentation.

PFP – Interaction with other fire safety systems and the fire strategy

In the Middle East identifying the key challenges in fire safety design and escape planning, particularly in tall and super-tall towers, requires a careful balance of architectural vision with fire safety provisions in the high-rise building design. It is important for the design team to assess the unique considerations for fire safety in tall buildings including:

• Potential for flame spread both internally and externally
• Challenges in fire suppression
• Extended exposure to smoke and heat
• Potential for thermal weakening of the building structure

From a design perspective the requirements for the components of egress must be fully considered by the project team. A full analysis of the interaction between the following components must be undertaken:

• Horizontal components of escape
• Vertical components
• Areas of relative safety
• Place of ultimate safety

In addition, the building design should fully address the requirements for:

• Structural fire protection
• Fire suppression – reliability & robustness
• Smoke control
• Compartmentation
• Evacuation strategies
• Fire service access and facilities
• Fire safety management & evacuation planning

It can be seen from the above items that fire compartmentation plays a key factor in the overall building fire safety provisions but is also complemented by other active systems to achieve a full safety package which should be fully detailed within the fire strategy.

As highlighted above the provision of fire compartmentation as part of the overarching fire strategy is used to achieve a number of goals, although its primary consideration is usually the protection of the means of escape. In some buildings, there may be minimal or no other fire separation other than for the protection of the means of escape i.e. a simple office building of limited size served by a single stair. The floor area may be open plan, with no partitions, however, the stair will be enclosed by fire walls (and fire doors) to ensure a fire within any part of the accommodation cannot pass into the stair. Where building designs become more complex and larger in size/area, the objectives and reliance on fire compartmentation is usually increased.

Compartmentation falls into the passive rather than active category as it typically doesn’t react or change in a fire condition. This can be viewed as one of its many advantages, as a feature, it is effectively a capital cost and can have little maintenance requirements, i.e. a masonry wall once completed will require minimal maintenance throughout its ‘life’, however it’s importance shouldn’t be overlooked and regular checks should be made to ensure its integrity is maintained. The most common problem with fire separation is that it frequently requires openings to be provided, whether this is for general communication for the building occupants (people passing through fire doors etc.) or building services, thus creating openings and therefore weaknesses within the separation. Specialist attention needs to be given to these breaches and the fire rating requirement should be recorded on fire safety drawings and provided with appropriate signage in situ to identify its fire rating etc.

Firestopping is the generic term given to various components that are used to seal openings in fire compartmentation. The method adopted will differ greatly, depending on the type and size of the opening as well as the material that is passing through. Other systems, such as fire dampers are used where ductwork passes through fire walls. Technology and industry advances mean that fire separation (if installed properly) can have an enviable success rate, however, it is the weaknesses that must be continually considered, particularly with the constant changing environment in buildings requiring service alterations.

Often following an incident the shortfalls in the installed fire compartmentation are highlighted by the spread of fire within a building. Experience indicates a number of areas that are mismanaged in terms of fire separation. Cavity barriers are a form of fire separation, placed in areas where fire and smoke spread could occur and go undetected, commonly this is not adequately achieved within roof voids, increasing the risk of fire spread within the building. Similarly, deficiencies have been identified within both ceiling and floor voids. The level of deficiencies normally depends on the time of construction, newer buildings, built to current regulations, using modern building systems should have less problems, however, poor quality construction management can lead to ineffective systems being installed and where refurbishments have been undertaken in existing buildings, large un-separated areas can often be identified.

Fire compartmentation should be included as a significant consideration of an existing buildings fire risk assessment and is an area where competency is critical. Fire safety managers should have a comprehensive understanding of their buildings fire strategy and individual fire safety components, particularly the fire compartmentation, which should be frequently checked with a frequency similar to active systems. Prior to a building’s completion the passive fire protection should be checked and verified as meeting the requirements of the fire strategy before being signed off as acceptable by a suitably trained, experienced and competent fire engineer.

For more information, go to www.warringtonfire.com