The two illustrations depict ventilators that have automatically opened and essentially a chimney effect is created in the ventilation shaft.
Ventilators on other floors remain closed to inhibit the spread of smoke.
Lobby Ventilation - vents shown in red
Ventilators may be installed into the walls at the end of corridors, which automatically open in the event of a fire.
With enclosed corridors and lobbies, a combined system of smoke dampers, ducting or smoke shafts and natural ventilators can be required instead.
7.5 Maximum travel distances Travel distance is measured from any point in the building to a place of safety (i.e. relative or ultimate). Travel distance will depend on how quickly people will react and make their escape and how long it will be before the fire prevents that movement to the escape route.
7.6 Places of Relative Safety It is often necessary to devise a temporary place of safety, such as when evacuating high buildings. This may be defined as a place of comparative safety and includes any place which puts an effective barrier (normally 30 minutes fire resistance) between the person escaping and the fire.
Examples are as follows:
1. A story exit into a protected stairway or to the lobby of a lobby approach stairway.
2. A door in a compartment wall or separating wall leading to an alternative exit.
3. A door which leads directly to a protected stair or a final exit via a protected corridor.
A staircase which is enclosed throughout its height by fire resisting structure and doors can usually be considered to be a place of comparative safety. In these cases, the staircase can be known as "a protected route".
7.7 Place of Ultimate Safety Ideally, this should be in the open air where dispersal away from the building can be achieved. Escape routes should never discharge finally into enclosed areas or yards unless the dispersal area is large enough to permit all the occupants to proceed to a safe distance. Total dispersal in the open air, therefore, constitutes ultimate safety. When inspecting any building, it is important always to follow the escape route to its ultimate place of safety.
7.8 Travel Distance in one direction only
Travel Distances
Occupancy
Escape In More Than One Direction Residential Institutions Old Peoples Homes Hospital Wards Hotels Offices Shops Factories Storage / Warehouse
Escape In One Direction Only
15m 9m 15m 15m 25m 18m 25m * 18m
32m 18m 32m 32m 45m 30m 45m * 45m Notes: * Distance varies with the risk attached to the process carried out or the materials involved, etc.
If there is only one exit, then a person may have to travel towards the fire. (Escape in one direction only)
If a room or compartment has two or more exits, (escape in more than one direction) then a person escaping can turn their back on the fire.
7.9 Occupancy Calculations In establishing the basic occupancy of a building, principal factors are the number of persons who would ‘normally’ be in the building, the variable factor of whom may also use the building.
The number of occupants for an existing building with a reasonably fixed population may be ascertained by questioning the responsible person. In ascertaining the occupancy of a building such as a theatre or sports ground, the number can be arrived by counting the number of seats.
In unoccupied buildings, the occupancy figure is arrived at by the density factor.
Density factors vary dependent upon the use of premises i.e. domestic, retail, restaurant etc.
Density factors are specified in the following documents:
• Guide to Fire Precautions in Existing Places of Entertainment and Like Premises.
• Guide to Safety at Sports Grounds.
• Also in the BS 5588 series of documents.
• Building Regulations 2000 - Approved Document B Extract has shown below:
To ascertain the maximum numbers of people, you need to calculate the floor space, delete the area of permanent features, i.e. stairs, toilets, lifts, escalators, corridors and other circulation spaces. What is left is the usable floor space and this is divided by the density factor, giving you the number of people able to occupy that area.
You should also consider that most premises and indeed a story of a building will probably be made up of areas of more than one use. So using the density factor table and setting an example of an exhibition hall, the candidate should also consider that within the exhibition hall there could also be a sales area and a conference room.
As different parts of the exhibition centre are put to different uses, it refugee necessary to use different density factors.
7.10 Time of evacuation. Time of evacuation is derived from building construction and occupancy
The construction of buildings is divided into three basic types,
Class A - complete non-combustible construction, i.e. elements of structure, floors and walls. Supporting structure of brick or concrete. Class B - traditional construction, i.e. non-combustible walls with combustible floors. Class C - combustible construction, i.e. timber floors and walls.
Based on these classes, arbitrary evacuation times were decided upon and generally accepted as –
Class 'A' construction - 3 minutes. Class 'B' construction – 2.5 minutes. Class 'C' construction - 2 minutes.
These are provisional times and can be extended or reduced according to the particular circumstances.
7.11 Exit Widths The width of exits required depends on the number of occupants, the rate of flow and the 'flow time', and is expressed by the formula:
U = N / (40 x T)
U = number of units required N = number of occupants 40 = standard rate of flow and is applied in two calculations T = Flow time ( i.e. 3 minuets for Class 'A', 2.5 minutes for Class 'B' and 2 minutes for Class 'C')
When the number of units is less than a whole number and the fraction is greater than or equal to 0.3, it should be rounded up.
7.12 Number of Exits The minimum number of exits depends upon the number of units of exit width required and the maximum size of any particular exit, and is demonstrated by the formula:
E = U / 4 + 1 E = number of exits U = number of units of exit width (from exit width formula) 4 = size of largest exit permitted. 1 added to ensure there would always be at least one unit.
The candidate should now calculate widths and number of exits using the exhibition hall example. It may be of interest to the candidate to research how standard rate of flow was arrived at.
Ventilators on other floors remain closed to inhibit the spread of smoke.
Lobby Ventilation - vents shown in red
Ventilators may be installed into the walls at the end of corridors, which automatically open in the event of a fire.
With enclosed corridors and lobbies, a combined system of smoke dampers, ducting or smoke shafts and natural ventilators can be required instead.
7.5 Maximum travel distances Travel distance is measured from any point in the building to a place of safety (i.e. relative or ultimate). Travel distance will depend on how quickly people will react and make their escape and how long it will be before the fire prevents that movement to the escape route.
7.6 Places of Relative Safety It is often necessary to devise a temporary place of safety, such as when evacuating high buildings. This may be defined as a place of comparative safety and includes any place which puts an effective barrier (normally 30 minutes fire resistance) between the person escaping and the fire.
Examples are as follows:
1. A story exit into a protected stairway or to the lobby of a lobby approach stairway.
2. A door in a compartment wall or separating wall leading to an alternative exit.
3. A door which leads directly to a protected stair or a final exit via a protected corridor.
A staircase which is enclosed throughout its height by fire resisting structure and doors can usually be considered to be a place of comparative safety. In these cases, the staircase can be known as "a protected route".
7.7 Place of Ultimate Safety Ideally, this should be in the open air where dispersal away from the building can be achieved. Escape routes should never discharge finally into enclosed areas or yards unless the dispersal area is large enough to permit all the occupants to proceed to a safe distance. Total dispersal in the open air, therefore, constitutes ultimate safety. When inspecting any building, it is important always to follow the escape route to its ultimate place of safety.
7.8 Travel Distance in one direction only
Travel Distances
Occupancy
Escape In More Than One Direction Residential Institutions Old Peoples Homes Hospital Wards Hotels Offices Shops Factories Storage / Warehouse
Escape In One Direction Only
15m 9m 15m 15m 25m 18m 25m * 18m
32m 18m 32m 32m 45m 30m 45m * 45m Notes: * Distance varies with the risk attached to the process carried out or the materials involved, etc.
If there is only one exit, then a person may have to travel towards the fire. (Escape in one direction only)
If a room or compartment has two or more exits, (escape in more than one direction) then a person escaping can turn their back on the fire.
7.9 Occupancy Calculations In establishing the basic occupancy of a building, principal factors are the number of persons who would ‘normally’ be in the building, the variable factor of whom may also use the building.
The number of occupants for an existing building with a reasonably fixed population may be ascertained by questioning the responsible person. In ascertaining the occupancy of a building such as a theatre or sports ground, the number can be arrived by counting the number of seats.
In unoccupied buildings, the occupancy figure is arrived at by the density factor.
Density factors vary dependent upon the use of premises i.e. domestic, retail, restaurant etc.
Density factors are specified in the following documents:
• Guide to Fire Precautions in Existing Places of Entertainment and Like Premises.
• Guide to Safety at Sports Grounds.
• Also in the BS 5588 series of documents.
• Building Regulations 2000 - Approved Document B Extract has shown below:
To ascertain the maximum numbers of people, you need to calculate the floor space, delete the area of permanent features, i.e. stairs, toilets, lifts, escalators, corridors and other circulation spaces. What is left is the usable floor space and this is divided by the density factor, giving you the number of people able to occupy that area.
You should also consider that most premises and indeed a story of a building will probably be made up of areas of more than one use. So using the density factor table and setting an example of an exhibition hall, the candidate should also consider that within the exhibition hall there could also be a sales area and a conference room.
As different parts of the exhibition centre are put to different uses, it refugee necessary to use different density factors.
7.10 Time of evacuation. Time of evacuation is derived from building construction and occupancy
The construction of buildings is divided into three basic types,
Class A - complete non-combustible construction, i.e. elements of structure, floors and walls. Supporting structure of brick or concrete. Class B - traditional construction, i.e. non-combustible walls with combustible floors. Class C - combustible construction, i.e. timber floors and walls.
Based on these classes, arbitrary evacuation times were decided upon and generally accepted as –
Class 'A' construction - 3 minutes. Class 'B' construction – 2.5 minutes. Class 'C' construction - 2 minutes.
These are provisional times and can be extended or reduced according to the particular circumstances.
7.11 Exit Widths The width of exits required depends on the number of occupants, the rate of flow and the 'flow time', and is expressed by the formula:
U = N / (40 x T)
U = number of units required N = number of occupants 40 = standard rate of flow and is applied in two calculations T = Flow time ( i.e. 3 minuets for Class 'A', 2.5 minutes for Class 'B' and 2 minutes for Class 'C')
When the number of units is less than a whole number and the fraction is greater than or equal to 0.3, it should be rounded up.
7.12 Number of Exits The minimum number of exits depends upon the number of units of exit width required and the maximum size of any particular exit, and is demonstrated by the formula:
E = U / 4 + 1 E = number of exits U = number of units of exit width (from exit width formula) 4 = size of largest exit permitted. 1 added to ensure there would always be at least one unit.
The candidate should now calculate widths and number of exits using the exhibition hall example. It may be of interest to the candidate to research how standard rate of flow was arrived at.
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