PAUL HAY Capital Projects

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Fire Protection: Physical Requirements, Lightning Protection, Detection & Alarm Systems

Author:          Paul Hay

e-mail:            paul.hay@phcjam.com

profile:           www.linkedin.com/in/phcjam

1.0  INTRODUCTION TO FIRE PROTECTION

1.1        Objectives of fire protection are (a) protection of life, (b) protection of property, and (c) continuation of operation.

1.2       Fire Protection involves (a) fire resistance, (b) lightning protection, (c) fire detection, (d) smoke management and (e) fire suppression.

1.3       Fires can only be sustained if fuel, high temperature and oxygen are all present.

1.4       Structure and contents of a building serve as fuel for fires.

1.5       There are three sources of ignition:

1.5.1   Chemical ignition occurs when volatile substances spontaneously combust under normal temperatures or exposure to open flame;

1.5.2   Electrical ignition occurs when heat is supplied by electrical sources such as arcing or static electricity (e.g. lightning);

1.5.3   Mechanical ignition occurs when heat is produced by friction (e.g. overheating equipment).

1.6       Fires develop in four stages:

1.6.1   At the incipient stage, there is no perception of smoke, flame or appreciable heat;

1.6.2   At the smoldering stage, smoke is visible but there is no flame or appreciable heat;

1.6.3   At the flame stage, appreciable heat is not present;

1.6.4   At the heat stage, smoke, flame and appreciable heat are present.

2.0 THE SITE MUST BE PLANNED TO FACILITATE FIRE PROTECTION

2.1     Unobstructed access must be provided for fire apparatus such as pumpers, ladder trucks and tankers:

2.1.1   Ideally, fire trucks should be able to pull alongside every external wall;

2.1.2   The width of driveways should permit full extension of aerial ladders:

W =     (H - 1.8) Cot α + 1.2                                                                              [2.1]

where,

W =     Distance of far-side of truck from external wall, m

H =      Height to which ladder is to be extended, m

α =       Angle of ladder to roadway (60 deg.> α >80deg.)

2.1.3   Utility poles, wide podiums, outdoor sculptures, fountains, etc. can obstruct the use of aerial ladders;

                        2.1.4   Ordinary fire-fighting apparatus can only extend seven storeys.

2.2       Hydrants should be properly located:

2.2.1   They should be installed 0.6 m - 3 m in from a curb;

2.2.2   They should be located at intersections and be no further than 9 m apart.

2.3       Proper outdoor illumination allows swift location of hydrants.       

2.4       Siamese connections should be within 6m from an hydrant and should be visible and conspicuously marked.

2.5       Proximity to highly flammable surroundings increases the risk of fires:

2.5.1   Firewall construction is a viable option;

2.5.2   Water storage for suppression is another; and

2.5.3   External water sprinklers may be placed adjacent to the building's openings.

2.6       More reliance will have to be made of internal systems when the above are not addressed.

3.0 EGRESS SHOULD BE PLANNED TO FACILITATE FIRE PROTECTION

3.1       Buildings should facilitate evacuation on detection of a fire, until fire-fighters arrive:

3.1.1   At least two exits should be provided;

3.1.2   Means of egress should be provided to theses exits;

3.1.3   Elevators are not means of egress.

3.2       Exit signs must be connected to batteries or emergency power.

3.3       Building Codes specify (a) number of exits required, (b) minimum widths of doorways, (c) minimum width of means of egress, and (d) maximum lengths of means of egress:

3.3.1   Automatic door closures should be used at exit corridors and stairwells;

3.3.2   Distances increase with use of sprinkler systems.

3.4       Building codes also specify the maximum permissible floor area and heights with regard to the building use:

3.4.1   Larger areas need fire walls;

3.4.2   Doors to fire walls may be kept open by door hardware but should close in the event of a fire being detected;

3.4.3   Fire dampers are required in ducts passing through fire walls;

3.4.4   Attention should be paid to vertical openings, as the vertical spread of flame is more important than the horizontal spread.

4.0  BUILDING COMPONENTS MUST BE SELECTED FOR FIRE PROTECTION    

4.1    Building codes specify the fire resistance ratings required for building components depending on the distance from site boundaries or adjacent buildings:

4.1.1   Fire ratings of components are expressed in hours;

4.1.2   Intumescent coatings expand when exposed to fires;

4.1.3   Un-rated and non-combustible materials are allowed in some instances.

4.2     Where sprinkler systems are used, floors should be waterproof and detailed for quick removal of water to facilitate continuity of operation.

5.0 HIGH BUILDINGS HAVE SPECIAL REQUIREMENTS FOR FIRE PROTECTION

5.1     Buildings over 7-storeys high should have electrical generators capable of providing emergency power to (a) fire alarm system, (b) exit and emergency lighting, (c) required ventilation system, (d) fire suppression system, (e) voice communication system and (f) fire elevator.

5.2       High-rise buildings should have at least one elevator connected to emergency power.

5.3       Refuge Areas are required to hold persons unable to evacuate: 

5.3.1   Areas must be able to accommodate all occupants of a floor;

5.3.2   Areas must be adjacent to the escape route; and

5.3.2   Areas must be constructed with materials of high fire resistance ratings.

5.4       Tall structures may have smoke tower stair shafts:

5.4.1   Entrance to stairwell is through a vestibule;

          5.4.2   Pressure differential between (a) stairwell and vestibule, and (b) vestibule and floor area are maintained by separate supply and exhaust fans run on emergency power.

6.0 LIGHTNING PROTECTION IS REQUIRED FOR VULNERABLE BUILDINGS

6.1       The average discharge of lightning is 200 x 10⁶ volts at 30,000 amps:

6.1.1   Cold lightning bolts can shatter and kill but not ignite combustibles;

6.1.2   Hot lightning bolts will ignite combustibles as well as shatter and kill.

6.2       There are four important factors to consider:

6.2.1   Frequency and severity of thunderstorms;

6.2.2   The building's exposure;

6.2.3   Indirect effects, such as losing a water tank; and

6.2.4   The value and nature of the buildings contents.

6.3       Lightning protection involves provision of a continuous metallic path to ground:

6.3.1   Air terminals/Lightning rods shall be spaced no further than 6m on centre around the perimeter of a flat roof, or along the ridge of a pitched roof;

6.3.2   Additional terminals shall be spaced no further than 15 m apart in the middle of large open roofs;

6.3.3   All terminals shall be inter-connected;

6.3.4   The roof perimeter shall be grounded by down leads no further than 30 m apart;

6.3.5   Large metal objects (e.g. VAC units must be bonded to the conductor; and

6.3.6   Smaller metal objects (e.g. roof drains) which are less than 1.8 m from a conductor should also be bonded.

7.0  FIRE DETECTION SYSTEMS GIVE EARLY WARNING OF HAZARD

7.1       Fire alarms operate in three stages: (a) signal initiation, (b) signal processing, and (c) alarm indication.

7.1.1   Signal Initiation can be manual or automatic;

7.1.2   Control equipment, such as Annunciators, process the signal;

7.1.3   An audible, and sometimes visible, alarm is activated.

7.2       Manual fire alarm stations are wall-mounted devices used to activate fire alarms:

7.2.1   Alarm stations and alarms are placed in the path of egress;

7.2.2   Stations can be coded or non-coded:

7.2.2.1            Coded stations make audible alarms that identify the device initiated;

7.2.2.2            Coded stations are recommended when over 10-stations are proposed;

7.2.2.3            Annunciator panels identify where non-coded stations are initiated.

7.3       Smoke Detectors are automatic devices powered by either AC or DC power supply:

7.3.1   Protective wiring or conduits are required if AC power is used;

7.3.2   Smoke and gas inhalation is responsible for 75% of fire-related deaths; and

7.3.3   Fires are responsible for the remaining deaths.

7.4       Five types of smoke detectors are available:

7.4.1   Ionization detectors initiate an alarm when combustion particles are generated at the incipient stage of a fire;

7.4.2   Photo-electric detectors initiate an alarm at the smoldering stage;

7.4.3   Ultra-violet (UV) and Infrared (IR) detectors initiate an alarm at the flame stage:

7.4.3.1            UV detectors are best installed in rooms used to store highly flammable or explosive substances;

7.4.3.2            IR detectors are typically installed in enclosed spaces;

7.4.3.3            The sensitivity of either detector can be adjusted to ignore other sources of UV or IR radiation.

7.4.4   Heat detectors sense temperature and initiate an alarm when the temperature or rise in temperature exceeds a threshold value.

7.5       Care should be exercised in locating smoke detectors to prevent false alarms:

7.5.1   Areas with high humidity or steam (e.g. laundries) should be avoided;

7.5.2   Areas with open flames (e.g. labs) should be avoided;

7.5.3   Areas with exhaust gases (e.g. garages) should be avoided;

7.5.4   Designated smoking areas should be avoided;

7.5.5   Areas that are dust laden should be avoided;

7.5.6   Areas with high air movement (e.g. exit doors) should be avoided.

7.6       Where fires can occur in several stages, different types of detectors can be specified.

7.7       Alarms activate bells, horns, or strobes for swift evacuation:

7.7.1   Coded alarms initially sound an audible code and can be programmed to ring continuously afterwards;

7.7.2   Zone coding is more economical than device coding;

7.7.3   Un-coded alarms ring continuously:

7.7.3.1            Devices can be arranged into zones with annunciator panels;

7.7.3.2            The annunciator will identify the alarm zone.

7.8       Water-flow switches placed on sprinkler piping can initiate a signal to an annunciator.

7.9       Alarm systems are available that can activate smoke removal systems, re-route elevators and activate fire suppression systems.

8.0 FIRE ALARM SYSTEMS SHOULD BE SPECIFIED ACCORDING TO THE BUILDING TYPE

8.1       Small facilities, including residential buildings, should use Local Protective Signaling:

8.1.1   An alarm is only made at the affected premises;

8.1.2   Fire Department is notified manually by occupant, neighbour, or passer-by;

8.2     Public buildings (e.g. schools, government offices, museums, etc.) should use Protective Signaling:

8.2.1   This system is essentially local protective signaling with a direct connection to a municipal fire alarm box;

8.2.2   Alarms are automatically relayed to the Fire Department.

8.3       Private facilities (e.g. shops and offices) which are unoccupied for extended periods of time should use Remote Station Protective Signaling:

8.3.1   This is essentially local protective signaling which automatically dials a pre-selected telephone number;

8.3.2   Alarms are communicated to a remote location that is always manned;

8.3.3   The remote office is responsible for taking further action.  

8.4    Large multi-building facilities (e.g. universities, manufacturing plants, etc.) should use Propriety Protection Signaling:

8.4.1   Alarms are relayed to a central control station on the site manned by personnel associated with the facility;

8.4.2   The control room is generally in a security post or supervisory location such as an Energy Management Department;

8.4.3   Signal transmitted to the control room identifies the exact location or zone within the affected building;

8.4.4   The Fire Department is contacted manually after verification. 

FURTHER READING

            Mechanical and Electrical Equipment for Buildings, 8^th edition, Benjamin Stein, John S. Reynolds, John Wiley & Sons Inc., USA, 1992

Construction Materials & Processes, Don G. Watson, McGrawHill Book Co., USA, 1978;

            Ramsey/Sleeper Architectural Graphic Standards, AIA, Robert T. Packard (ed), John Wiley & Sons Inc., USA, 1981;

Architectural Handbook, Alfred M. Kemper, John Wiley & Sons Inc., USA, 1979