Occupational Health & Safety Practitioner. Reading BUILDING FIRE SAFETY

Transcription

1 Occupational Health & Safety Practitioner Reading BUILDING FIRE SAFETY January 2009

2 Contents OVERVIEW...1 SECTION 1: INTRODUCTION...2 SECTION 2: BUILDING CLASSIFICATIONS...4 SECTION 3: PASSIVE AND ACTIVE FIRE SAFETY SYSTEMS...7 SECTION 4: BUILDING PERFORMANCE...12 SUMMARY...14 REFERENCES AND FURTHER READING...14 Government of Western Australia Department of Commerce Published by WorkSafe, PO Box 294, WEST PERTH WA Tel: Toll Free The SafetyLine Institute material has been prepared and published as part of Western Australia s contribution to national OHS skills development State of Western Australia. All rights reserved. Details of copyright conditions are published at the SafetyLine Institute website. Before using this publication note should be taken of the Disclaimer, which is published at the SafetyLine Institute website.

3 OVERVIEW This reading provides an introduction to underlying principles of fire safety including objectives of fire safety, the division of buildings into various classes relating to fire safety requirements, and passive and active fire safety systems. Objectives After reading this information you should have a basic understanding of how a multi-storey office building functions in a fire. Author Danny Spadaccini JANUARY 2009 SAFETYLINE INSTITUTE PAGE 1

4 Section 1: INTRODUCTION Glossary of terms When they are first used, glossary terms are indicated with an asterisk (*). Make sure that you are familiar with the Glossary of terms before going any further. Fire Fire Separation Fire Resistance Level (FRL) The state of combustion in which inflammable material burns, producing heat, flames and often smoke. The use of a wall, that divides a storey or building, to resist the spread of fire or smoke. The grading period given in minutes for Structural Adequacy (ability to maintain load); Integrity (ability to prevent passage of flames and hot gases); and Insulation (ability to maintain surface temperature). It is expressed as 90/90/ Fire safety of a building is important Building safety in relation to fire* has been an important social and economic factor to the human race for thousands of years. Fire provides heat to our homes and places of work; it powers, directly or indirectly, much of the machinery and appliances in factories and homes; and generally contributes to the standard of living throughout most of the modern world. PAGE 2 SAFETYLINE INSTITUTE JANUARY 2009

5 1.2 Historical perspective History shows that fire was recognised as a threat to great civilisations as early as 2000 years ago. The Roman Empire devised a system of corps vigilante whose sole task was to be on watch for the outbreak of fire. The Great Fire of London in 1666 became the catalyst for the modern day building codes. The fire broke out in a baker's shop and destroyed half of London. The buildings in London at that time were not fire separated and so the fire spread easily. Analysis of how the fire spread led to the creation of the first building regulations. 1.3 Consequences of a fire When fire is not controlled the result can be: KEY POINT Fire Separation*: the use of wall that divides a storey or building to resist the spread of fire or smoke. death and injury of people who cannot escape its smoke, gases and heat; destruction of buildings, their contents and other tangible property; temporary or permanent closure of business, loss of income and possibly bankruptcy; and destruction of irreplaceable reminders of human heritage. 1.4 Basic fire safety concepts Building fire safety takes into account: safe egress (exit) from the building for occupants; facilities for fighting fire within buildings; prevention of spread of fire to adjoining properties; and access and egress for fire fighting personnel. JANUARY 2009 SAFETYLINE INSTITUTE PAGE 3

6 Section 2: BUILDING CLASSIFICATIONS 2.1 Ten occupancy classes for buildings In Australia, the Building Codes divide buildings into the following occupancy classes: 1. Single Dwelling 2. A Building containing 2 or more sole occupancy units, each being a single dwelling. 3. A residential building, other than a building of Class 1 or 2, which is a common place of long term or transient living for a number of unrelated persons, including: boarding house, guest house, hostel, lodging house, or backpackers' accommodation; or a residential part of an hotel or motel; or a residential part of a school; or accommodation for the aged, disabled or children; or a residential part of a health care building which accommodates members of staff. 4. A dwelling in a building that is in a Class 5, 6, 7, 8, or 9 if it is the only dwelling in the building. 5. An office or building used for professional or commercial purposes excluding classes 6,7,8, and A shop or other building for the sale of goods by retail or the supply of services direct to the public, including: an eating room, cafe, restaurant, milk or soft drink bar; or a dining room, bar, shop or kiosk part of a hotel or motel; or a hairdresser's or barber's shop, public launderer, undertaker's establishment; or market or sale room, showroom, or service station. PAGE 4 SAFETYLINE INSTITUTE JANUARY 2009

7 7. A building which is: a carpark; or for storage, or display of goods or produce for sale by wholesale. 8. A laboratory, or a building in which a handicraft or process for the production, assembling, altering, repairing, packaging and/or finishing of goods or produce is carried out for trade, sale or gain. 9. A building of public nature: a health care building, including those set aside as a laboratory; or an assembly building, including a trade workshop, laboratory, or the like in a primary or secondary school, but excluding any other parts of the building that are another class. 10. A non-habitable structure: a non-habitable building being a private garage, carport, shed, or the like; or a structure being a fence, mast, antenna, retaining or free standing wall, swimming pool or the like. 2.2 Why have classifications? Characteristics of occupants The characteristics of each type of classification are linked to life safety as each of these classes has certain KEY POINT features that impact on an occupant's safe egress. Effective building fire safety must Factors relating to the take into account characteristics of the capabilities of occupants influence safe egress. persons who can be expected to occupy the building including: age and mobility; awareness of fire; knowledge of the environment; density of occupancy; and control of occupants (impact of smoke on human behaviour). JANUARY 2009 SAFETYLINE INSTITUTE PAGE 5

8 The various classes take into account the variable characteristics of occupants, thus the many differing requirements for types of building. For example, the egress capabilities of an aged care wing of a hospital would differ greatly to that of an office where most employees would be able to exit the building without any assistance. A further example of this is a primary school where the majority of occupants (children) would require direct supervision to escape as compared to a warehouse whose employees would not require the same level of supervision for egress. Characteristics of the building The Building Code also takes into account other essential issues which can affect the performance of the building, such as the construction characteristics of the building. All buildings fall into three classifications of construction, being Type A, B & C. Type A is the form of construction with the highest fire resistant requirements, while type C has the lowest. The relationship between occupancy class, type of construction, and number of storeys is illustrated by the following chart. NUMBER OF STOREYS OCCUPANCY CLASS FLAT HOTEL OFFICE SHOP WAREHOUSE FACTORY PUBLIC 4 or more A A A A A A A 3 A A B B B B A 2 B B C C C C B 1 C C C C C C C DAY/ NIGHT DAY/ NIGHT DAY TIME DAY TIME STORAGE INDUSTRIAL CARE/ ASSEMBLY In addition to the type of construction used, many other components are required by the Building Code as the building size and complexity increases. Two examples are hose-reels and emergency lighting. The requirements for hose-reels and their locations vary, being dependent on the classification and size of the building. The requirements for emergency lighting are related to the classification of the building and the amount of floor area. KEY POINT The Building Code states the construction and fire safety requirements necessary. PAGE 6 SAFETYLINE INSTITUTE JANUARY 2009

9 Section 3: PASSIVE AND ACTIVE FIRE SAFETY SYSTEMS 3.1 Passive and active systems create the fire safety package for the building The features within a building can be broken down into passive and active systems for building fire safety. Passive systems are the permanent fixtures of the building such as fire rated floors, ceilings, walls, fire-isolated exits and columns. Active systems are services and equipment such as exit signs, emergency lighting, hydrants, hose-reels, smoke control, sprinklers, smoke and heat detectors, voice alarms, and fire indicator panels. The combination of these creates the Fire Safety Package for a building. By looking at a model building an overview of the workings of the passive and active systems within the building can be made. For the purposes of this example, we will look at a class 5 (office) multi-storey building. This will illustrate the functions of the various components of the building. It is important to note at this point that the Passive and Active systems within a building can be designed in many different ways to achieve the same objectives required for the structure. A fire starts at 12.00am on the third floor at a power point under a large desk in an archives section and quickly ignites files and assorted boxes stored under the desk. The archives section is vacant from 12.00am to 1.00pm due to the lunch break of the Archives Officer. For the purposes of the exercise, the assessment will be of a building without sprinklers. JANUARY 2009 SAFETYLINE INSTITUTE PAGE 7

10 3.2 Active systems detect the fire The smoke detection system would detect the smoke plume from the fire within 2-5 minutes of the fire starting. It is important to realise that detection of fire by the building occupants' senses of sight, smell and hearing are quite often the first form of detection. With the smoke detector alarm system engaged a general alarm will be raised. Smoke detectors can be located in the return air ducts of the air conditioning or at ceiling level dispersed throughout the building. This alarm can include direct alarm to brigade as well as to the whole building. The alarm would alert Fire Wardens within the building who would stand-by at their designated phones. Photograph from Safety and Health, official publication of the National Safety Council. The Fire Warden of the Floor where the incident began would investigate the fire and if able to, start fighting the fire. If not able to control fire the warden will begin evacuation of the floor and, in conjunction with other wardens, evacuate the building if necessary. 3.3 Passive systems Fire Resistance Level Fire Resistance Level (FRL)* is the grading period given in minutes (expressed for example as 90/90/90) for: structural adequacy (ability to maintain load); integrity (ability to prevent passage of flames and hot gases); and insulation (ability to maintain surface temperature). PAGE 8 SAFETYLINE INSTITUTE JANUARY 2009

11 The building itself has now initiated alarm. This then leads onto all the fire systems within the building acting in unison. The floor upon which the fire is burning has a 120/120/120 FRL (2 hours Fire Resistance Level). This is a grading in minutes in which it would maintain its structural adequacy, integrity and insulation. Structural adequacy is the ability to maintain stability and load-bearing capacity; integrity is the ability to resist the passage of flames and gases; and insulation is the ability to maintain surface temperature. Any surrounding structural members of the building would also have similar ratings. The exit stairs would have a KEY POINT 180/120/120 rating providing safe access for occupants for a two hour period. The exit stairs Passive systems include are referred to as fire isolated which means the the fire rated floors, ceilings, walls, fire-isolated stairs have a fire resisting shaft (including walls exits and columns. and roof). The passive members of the fire systems prevent the spread of the fire to adjoining floors and allow safe egress whilst ensuring the structure does not collapse or allow the spread of smoke. 3.4 Active systems Air conditioning unit changes to exhaust mode The first detection of the fire sets a number of active systems in motion in the building. The air conditioning unit for the floor with the fire will alter its operation. The unit will go into a full exhaust mode drawing air from the floor. All other floors in the building will change to full return air mode. This ensures that a negative air pressure is maintained on the floor with the fire, drawing smoke out, and a positive air pressure is maintained on all other floors preventing the penetration of smoke. Depending on the design configuration chosen for the building stairwell, pressurisation may commence (see illustration below). Air is forced into the stairwell, creating a positive pressure, and preventing the penetration of smoke into the escape stairs. JANUARY 2009 SAFETYLINE INSTITUTE PAGE 9

12 Emergency lighting and exit signs At this stage emergency lighting and exit signs provide sufficient illumination for safe evacuation of the building. The exit signs include directional signs indicating the path to exits for occupants. The lift system cannot be used for escape in a fire and a warning sign is displayed stating so for all occupants. The fire brigade only can override the lifts for use in access for the fighting of the fire and for the purpose of evacuating people with disabilities. Fire fighting equipment Facilities installed for the fire brigade to assist in the fighting of the fire include fire hydrants, hose-reels, extinguishers and the lift as a stretcher evacuation facility if designated as such. KEY POINT Active systems include the exit signs, emergency lighting, hydrants and hose-reels, smoke detectors and sprinklers. 3.5 Event lines The following event lines provide an insight into the sequence in which various events occur within the building. PAGE 10 SAFETYLINE INSTITUTE JANUARY 2009

13 The first Event line illustrates the relationship between the development of a building fire, the progressive reduction of tenability and ability of occupants to escape. The second Event line illustrates the relationship between: the Fire; the Passive systems; the Active systems; and the People (occupant movement), and the sequence of events. JANUARY 2009 SAFETYLINE INSTITUTE PAGE 11

14 Section 4: BUILDING PERFORMANCE The Passive and Active systems within an office building can easily be disrupted and rendered inoperative by the occupants of the building. 4.1 Safe egress may be compromised Safe egress from a building is essential. This can be compromised by the following. Wedging open of exit doors to fire isolated stairs for floor to floor access. This greatly reduces the FRL (Fire Resistance Level) of the stair and also eliminates the function of stairwell pressurisation. The open door can allow smoke and flame penetration to the exit, eliminating its use for the floors above. Removal of fire door / exit door signs during maintenance such as painting. Occupants who may be unfamiliar with the building will not be able to locate exit doors. Storage of items in exit passages and stairs. The width of exit passages and stairs must not be used for storage. The path of travel to, in and from an exit should be free of obstructions at all times. Flammable objects such as cleaning fluids stored at the base of a stairwell can render an escape stair inoperative in an emergency. Desks, bookshelves and other objects can block a path of travel to an exit. Locking of exit doors for security purposes. Many office buildings have card access, which is connected to the alarm system and will not allow re-entry from an exit in an emergency. Once an escape stair has been entered in an emergency you should only be able to exit at final discharge point. No exit door should be locked at any time. The ramifications of this are occupants trapped in an exit unable to escape. Installations in fire-isolated exits. A fire-isolated exit must be maintained as its name suggests. Care must be taken to maintain the isolation of the exit. For example, carpet should not be a laid in such an exit. Discharge from exits. Exits must discharge to open space. An open space must not be a locked compound. The discharge point must not trap the occupants escaping. PAGE 12 SAFETYLINE INSTITUTE JANUARY 2009

15 4.2 Smoke control Internal partitioning and alterations do not always require approval from a Local Authority. The alteration to a floor plan in terms of high level partitioning affects the performance of air-conditioning units and smoke control. It is essential when major alterations are carried out that the design of the air-conditioning / smoke control be assessed, to ensure the original performance criteria are met. Plastic sheets cannot be taped over ducts as this alters the performance of air-conditioning. 4.3 Smoke detectors Partitioning and alterations can alter the function of detectors located at ceiling level. When partitioning is altered, the relative position of detectors may be changed so that spacings are not even or positions are not central within rooms, affecting the performance of detectors. 4.4 Emergency lighting and exit signs Partitioning and high level shelving can affect the effectiveness of emergency lighting and exit signs. Exit signs can be blocked from view and the level of illumination for the emergency lighting reduced below standard. 4.5 Hydrants, hose-reels and fire extinguishers Fire fighting equipment must be accessible at all times. The positioning of desks or shelving preventing access to fire fighting equipment must be prevented at all times. External access to hydrants for the fire brigade must be maintained in case of an emergency. JANUARY 2009 SAFETYLINE INSTITUTE PAGE 13

16 4.6 Fire rated structural components To maintain the Fire Rated Level (FRL) designed in a structural component, any alteration to it must be assessed. For example, additional penetrations to floors can allow spread of flame and gases. 4.7 Maintenance Safety installations in buildings must be adequately maintained to ensure their design performance. SUMMARY Building fire safety is an issue that must be addressed by all persons in the workplace. The fire systems in a building can be easily affected by the occupants and managers of the building. It is essential that persons who use a building understand the fire safety aspects of the building. By completing this reading you should have a basic understanding of how a building functions in a fire. These principles can be applied to your work place. Your feedback WorkSafe is committed to continuous improvement. If you take the time to complete the online Feedback Form at the SafetyLine Institute website you will assist us to maintain and improve our high standards. REFERENCES AND FURTHER READING Building Code of Australia PAGE 14 SAFETYLINE INSTITUTE JANUARY 2009