Thursday, April 02, 2009: 04:41:05 PM

Safety

FIRE PROOFING BUILDINGS

Underwriters Laboratory (UL) describes the fundamentals of fire safety for high-rise buildings. Times Journal of Construction and Design provides the details

Research in the field of fire protection is undergoing rapid development, and this will ensure that buildings are designed with more efficient fire-safety measures. After years of trial and error, we can now develop concepts and criteria that enable us to build high-rise buildings that are safe. To mitigate the sources of fire and losses due to it, planning at the architects’ table enables us to design a building that is protected against fires. Both active and passive fire defences provide reasonable safety from the effects of fire. Hence, a well-knit plan and its implementation in the design and construction of a high-rise residential building are essential to build a fire-safe structure.

Objectives
Effective fire-safe design begins with conscious analysis and decision-making early on in the design process. To effectively incorporate fire defences into a building’s design, the fire-safety objectives must first be identified. The acceptable levels of safety and the focus of fire-safety analysis and design process objectives are concentrated in the following areas:

  • Life safety
  • Property protection
  • Continuity of operation
  • Environmental protection.

Fire-safe design strategy
Fire-safe objectives can be met if fire ignition is prevented or if, given ignition, the fire can be managed. Evaluating a design for the building’s fire safety represents a systematic approach to the fire-safety strategy. These strategies can be identified as follows:

  • Prevent fire ignition
  • Controlling the combustion process
  • Controlling the fire by construction
  • Detect the fire early and provide notification
  • Automatically suppress the fire
  • Manually suppress the fire
  • Manage the exposed.

Prevent fire ignition
The first opportunity to ensure fire safety in a building is through fire prevention, which involves separating potential heat sources from potential fuels. Major building fires are started by heat sources and ignitable materials that are brought into the building and not built into it. This means that the design of the building from the architect and builder’s standpoint provides limited potential leverage on building future fire experience. For design purposes, fire prevention is enhanced by careful observance of codes and standards in the design and installation of electrical and lighting system, the heating system and any other built-in equipment such as cooking, refrigeration, air-conditioning, clothes washers and dryer. The venting system also needs to be carefully designed to carry carbon monoxide and potential fuels along protected paths. Protection from lightning and exposure to fires affects the external design of the building. A fire in one building creates an external fire hazard to the neighbouring structure by exposing those structures to heat or radiation and the possibility of convention currents and flying sparks of fire.

Underwriters Laboratories
Underwriters Laboratories (UL) is an independent, product-safety certification organisation that has been writing standards for safety and testing products for over a century. It is also a leading resource on fire safety and applies modern test methods and analyses to fire-related issues. UL is the first in the world to have a testing facility for building construction materials.

Combustion process control
Controlling the combustion process is concerned with slowing the fire in order to provide other fire safety measures with sufficient time to be effective. A systematic design for this purpose should address the possible ways through which hazards can grow rapidly. The building fire-safety system can be organised around fire growth and the results of combustion that is flame, heat, smoke and gases. The ease of generation and movement of these products are influenced by counter measures provided by the building. The effectiveness of the building fire-safety system determines the speed, quantity and path of movement of these products of combustion.

The main factors that influence controlling the combustion process are as follows:

  • Fuel load
  • Interior finish of the room
  • Air supply
  • Size, shape and construction of the room
  • Fire load.

Controlling the fire by construction
Fire-resistance barriers such as walls, partition and floors separate building spaces in order to delay or prevent fire from propagating from one place to another. In addition, barriers are important features in any fire-fighting operation because they dictate the size of the fire. The effectiveness of a barrier depends upon its inherent fire-resistance construction and its penetration. The use of flame-retardant paints, fire-stop barriers, firewalls, fire doors and windows are also some of the methods used to control the fire by appropriate construction of fire-safe buildings.

Fire detection and alarms
Fire detection is needed so that automatic or manual fire suppression will be initiated. Any other active fire-protection system will be activated and occupants will have time to move to safe locations, typically outside the building. One concern of rapid initial fire growth is that, after the detection, it can shrink the time available for life and property-saving responses.

Whatever the type of detection system hosen, it is important that, for each area of a building, a realistic assessment is made of the complication for response time after the fire is detected and before a lethal or high hazard condition develops. Alarm provision should not only involve installation of detection sensors but should also be designed to tell occupants what they need to do according to their location and their ability to respond. This would include the use of central annunciation panels and monitors to inform responsible staff.

Automatic suppression
To accomplish automatic suppression, detecting the fire and applying sufficient suppressants are necessary. For nearly a century and a half, automatic sprinklers have been the most important single system for the automatic control of hostile fires in buildings. Sprinklers operate directly over a fire and are not affected by smoke, toxic gases and reduced visibility. Less water is used because only those sprinklers operate that are fused by the heat of the fire. The major elements that determine the efficiency of the automatic extinguishing system are as follows:

  • Presence or absence of the system
  • Its reliability
  • The designing and extinguishing effectiveness of the system.

Manual suppression
The major aspect of this part of the building design includes the following:

  • The distance between the fire department and the building
  • Initial agent application
  • Fire extinguishment
  • Ventilation
  • Water storage and use
  • Water removability
  • Barrier effectiveness.

Managing the exposed
The design for life safety may involve one or a combination of the following factors:

  • Evacuation of the occupants
  • Protecting the occupants in an area
  • Providing an effective area of refuge
  • Practising the evacuation drill.

Fire impact can be lessened by managing the exposed, which involves people, property, operations, environment and/or heritage. The exposed people or property may be safeguarded by either moving them to a safe area or refuge or by protecting them at one location.


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