FIRE SAFETY STRATEGY - Stylusdataroom.stylus.london/wp-content/uploads/2019/02/Fire-Safety-Strategy.pdfThe report is based on the drawings supplied on the 2nd November 2017 by GPad

International Fire Consultants Ltd Head & Registered Office: Park Street Business Centre, Princes Risborough, Buckinghamshire, England HP27 9AH

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An International Fire Consultants Group Company

PRIVATE & CONFIDENTIAL

FIRE SAFETY STRATEGY

IFC Report FSS/14543/01C

112-116 Old Street London, EC1V

Prepared on behalf of: Coastview Estate Limited (London) 34a Rosslyn Hill London NW3 1NH

NOTE: This report should not be manipulated, abridged or otherwise presented without the written consent of International Fire Consultants Ltd

April 2018

Fire Safety Strategy IFC Report FSS/14543/01C 112-116 Old St., London Page 2 of 30

International Fire Consultants Ltd

ISSUE RECORD

Issue Date Recipient Comments

FSS/14543/01 23/09/2016 Coastview Estate Limited Issued for Comment

FSS/14543/01A 30.09.16 GPad Issue for B.Regs

FSS/14543/01B 06.11.17 GPad Updated following latest plans

FSS/14543/01C 20.04.18 GPad Updated following FRS

consultation

AMENDMENT RECORD

Date Paragraph Amendment

30.09.16 Table 1, 8.2, Figure 4

Updated re unprotected area design

06.11.17 Table 1, Figure 1, Table 3,

4.1.1, Figure 2,

7.4, 8.2

Updated following latest plans

20.04.18 Appendix A

added

ASET/RSET calculation updated to include disabled time flow

Dry riser moved from stair to lobby as requested by FRS

Revision 00 01 02 03

Author PM PM LM LM

Reviewer LM LM AS AS



1. EXECUTIVE SUMMARY

International Fire Consultants Ltd. (IFC) have been commissioned by Coastview Estate Ltd. to advise on the fire safety strategy for the proposed redevelopment at 112-116 Old Street, London.

This report outlines the Fire Safety Strategy for the proposed office block, and includes recommended fire safety provisions that will, in our opinion, demonstrate that the building design is capable of complying with the relevant functional requirements of the Building Regulations 2010 relating to fire safety.

The proposed redevelopment will consist of the alteration and extension of an existing 3 storey office building and the removal of an alternative escape stair.

The Fire Safety Strategy uses the recommended guidance contained within British Standard BS 9999 as a performance benchmark. BS 9999 requires a risk categorisation to be made of the building. All fire precautions are then based on the results of that categorisation.

It is expected that the information contained in this report will form the basis for Part B and Regulation 38 elements of the Building Regulations 2010 submission to the Building Control Body. Note that regarding the existing sections of the building, it is proposed that these storeys shall not have their fire precautions made more unsatisfactory than before, by the changes in use and layout.

It is envisaged that this report will be used to inform and assist the person or persons responsible for this building in the assessment of risk to work in the common areas with regard to fire as required by the Regulatory Reform (Fire Safety) Order 2005.



CONTENTS

1. EXECUTIVE SUMMARY .............................................................................................. 3

2. INTRODUCTION ....................................................................................................... 5

3. FIRE SAFETY SYSTEMS ............................................................................................. 7

3.1 FIRE ALARM AND DETECTION ....................................................................................... 7 3.2 SMOKE VENTILATION ................................................................................................ 7 3.3 SPRINKLER PROTECTION ............................................................................................ 8

4. MEANS OF ESCAPE ................................................................................................... 9

4.1.1 HORIZONTAL EGRESS ................................................................................................ 9 4.1.2 SMOKE VENTILATION OF COMMON STAIRS .................................................................... 11 4.1.3 GENERAL REQUIREMENTS ........................................................................................ 11 4.2 LIFE SAFETY POWER SUPPLY .................................................................................... 12 4.3 DISABLED EGRESS .................................................................................................. 12

5. EGRESS VIA REAR STAIR........................................................................................ 14

6. INTERNAL FIRE SPREAD (LININGS) ........................................................................ 18

7. INTERNAL FIRE SPEAD (STRUCTURE) ..................................................................... 19

7.1 STRUCTURAL FIRE RESISTANCE ................................................................................. 19 7.2 COMPARTMENTATION .............................................................................................. 19 7.3 PENETRATION AND LINEAR GAP SEALS ........................................................................ 20 7.4 CAVITY FIRE BARRIERS ........................................................................................... 20 7.5 THIRD PARTY CERTIFICATION ................................................................................... 21 7.6 CABLES ............................................................................................................... 21

8. EXTERNAL FIRE SPREAD ........................................................................................ 22

8.1 BUILDING SEPARATION AND BOUNDARY DISTANCES ....................................................... 22 8.2 EXTERNAL FIRE SPREAD CALCULATIONS ........................................................................ 22 8.3 REACTION TO FIRE ................................................................................................. 25 8.4 INSULATION ......................................................................................................... 25

9. ACCESS AND FACILITIES FOR THE FIRE AND RESCUE SERVICE ............................... 26

9.1 ACCESS ............................................................................................................... 26 9.2 FIRE-FIGHTING WATER ........................................................................................... 26 9.3 SMOKE VENTILATION .............................................................................................. 26

10. FIRE SAFETY MANAGEMENT ................................................................................... 27

11. CONCLUSION ......................................................................................................... 28

12. LIMITATIONS ........................................................................................................ 28

APPENDIX A...CFAST OUTPUT………………………………………………………………………………………….28



2. INTRODUCTION

The development is a proposed office redevelopment which will comprise 5 storeys, with 2 storeys added to the existing 3 storeys.

This fire safety strategy has been prepared in accordance with the recommended guidance of BS 9999.

The use of British Standards are intended to provide guidance for some of the more common building situations but alternative ways of achieving compliance with the requirements is acknowledged.

Where areas of the design depart from the general guidance and recommendations set out under BS 9999, it is proposed to adopt alternative solutions using performance based fire safety engineering in lieu of comprehensively meeting the guidance and recommendations discussed. A satisfactory standard of fire safety is to be achieved.

The report is based on the drawings supplied on the 2nd November 2017 by GPad Architecture & Interior Design and listed in Table 1. As the design of the building is an iterative process these drawings may not include all recommendations with this report.

Drawing

Number

Revision Drawing Description

408-FS.01 Proposed Courtyard Level Floor Plan

408-FS.02 Proposed Ground Floor Plan

408-FS.03 Proposed First Floor Plan

408-FS.04 Proposed Second Floor Plan

408-FS.05 Proposed Third Floor Plan

408-FS.06 Proposed Fourth Floor Plan

408.FS.07 Proposed Roof Plan

408-PA.10 Proposed Section A-A

SK32 Proposed West Elevation Fire Spread Calcs

Table 1 - Drawings reviewed

This report provides strategic information on means of escape and warning, internal and external fire spread and access and facilities for the Fire and Rescue Service (FRS). It is envisaged that this report will be used to inform and assist the person or persons responsible for this building in the assessment of risk to working in the common areas with relation to fire. As such this report should be considered along with the recommendations and findings of the risk assessment.

It is recommended that the building insurers be approached so that their requirements can be considered as part of the scheme.

It is also important that the building management have a clear understanding of the fire safety strategy adopted and of the operation and maintenance of the equipment designed to protect their lives and property.



The analysis may also, at the client’s request, consider the issues of property protection and business continuity although these are outside of Regulatory control and therefore not covered by this fire strategy report.

This report does not address contractor’s site fire safety issues during construction.



3. FIRE SAFETY SYSTEMS

3.1 Fire alarm and detection

A Category M manual detection and automatic alarm would be the minimum standard recommended in ADB. This would include manual call points adjacent to storey and final exits and located such that building occupants do not have to travel more than 45m to operate the alarm.

However, to enhance warning of a fire to the occupants and compensate for any deviations from the guidance recommendations (such as extended travel distances and reduced exit widths), and also to account for the potential for different tenants it is recommended that an automatic fire detection and alarm system be provided to at least an L3 standard, with detection in all escape routes, rooms adjoining escape routes and rooms/areas of high fire risk. Category L3 systems are designed such that warning of fire is given sufficiently early to enable all occupants, other than possibly those in the room of fire origin, to escape safely. General recommendations from BS 5839-11 should be followed. The provision of the L3 standard system will allow a 15% increase in travel distance limits and a reduction in exit width, although it is noted that the latter will not be applied in this instance as exit width is not problematic.

Fire alarm manual call points should be located at storey and building exits in order that the alarm can be manually sounded in the event of someone discovering fire prior to automatic detection. As there is the potential for nuisance activation of call points, it is recommended that new devices installed as part of the project are fitted with an alarmed cover.

Following alarm activation, a simultaneous evacuation should occur from all parts of the building.

A fire alarm control panel should be provided in the entrance lobby in order that any audible or visual alert signal can be identified by staff, and ideally should be visible from the outside to assist the fire service.

Audibility would be as per BS5839 Part 1 and therefore includes all the building including external terraces.

3.2 Smoke ventilation

As the basement level floor area is in excess of 200m2, a system of smoke and heat ventilation needs to be provided (to the main office not the SME unit). The basement level is to be connected to the Ground Floor level office via an open stair, hence they will form the same compartment. In this instance it is proposed that ventilation be provided by natural means with outlets to be provided at Ground Floor level. Smoke outlets should not be less than 2.5% of the floor area, which would equate to approximately 10.7m2 geometric opening area. These are manually openable by the fire service via a switch in the main stair. Outlets should also;

- Be sited at high level, either in the ceiling or in the wall of the space they serve;

1 BS 5839-1:2013, Fire detection and fire alarm systems for buildings. Code of practice for design, installation, commissioning and maintenance of systems in non-domestic premises.



- Be evenly distributed around the perimeter of the building, to discharge into the open air outside the building;

- Not be placed where they would prevent the use of escape routes from the building

Regarding the latter item, as will be discussed it will be necessary for occupants escaping using the rear stair to travel through the basement level lobby which separates the front stair from the office accommodation. As such, it will be necessary to demonstrate that occupants can escape safely whilst using this lobby before the Basement/Ground Floor office compartment fills with smoke to the extent that it could potentially impede egress via this route. This will be assessed in the next section of the report.

It is noted cross ventilation is not available however BS9999 does not propose cross ventilation when the basement is open on one side as here and the primary issue with opening vents at basement level is proximity of the escape route (ventilation at basement level may be possible post evacuation by the fire service).

Note that the lobby in question at basement level will also require a 1.0m2 Automatic Opening Vent (AOV), which should be designed to activate once smoke enters the lobby. The lobby being referred to is indicated below in Figure 1.

Figure 1 – Basement stair lobby ventilation

3.3 Sprinkler protection It is not proposed to provide sprinkler protection to this development.



4. MEANS OF ESCAPE The proposed building will consist of 2 stairs serving all levels.

4.1.1 Horizontal egress The travel distance limits for the building are listed in Table 2, based on the recommendations from BS9999.

Location Risk category

Maximum travel distance (m)

One-way travel

Two-way Travel

Office space & Reception area A21 25 63

Stores A21 25 63

Basement plant room A41,2 10 21 1 – 15% increase applied 2 – Note that BS 9999 states that mechanical plant rooms (which would include boiler rooms) are unacceptable without sprinklers. However IFC would consider that as long as the travel distances are short as those shown above, sprinklers would not be necessary or if plant rooms only serve ventilation equipment. This would need to be discussed with the relevant authorities.

Table 2 – Travel Distances

Based on the layouts provided, travel distances appear to be within acceptable limits from the office spaces and reception area. The occupancy levels for each area are indicated in Table 3, which are based on the floor area of each space/room and the relevant floor space factors outlined in BS 9999. BS 9999 uses 5m2/person for an office occupancy factor. It is understood however the Architect’s occupancy figures are based on 6m2/person for the office spaces.

Floor Use of space Floor area (m2)

Floor space factor (m2/p)

Occupancy (people)

Office space 340.5 6.0 57

SME Work space

70 6.0 12

Ground Floor Office space 426.3 6.0 72

Reception 60.8 N/A* 6

First Floor Office space 517.8 6.0 87

Second Floor Office space 516.4 6.0 87

Third Floor Office space 427.0 6.0 72

Fourth Floor Office space 306.6 6.0 52

Table 3 – Maximum occupancy levels

The minimum required escape width from each space is 800mm. The minimum required stair width for occupants moving downwards is 1000mm and 1200mm for occupants moving upwards to a final exit from the stair.



The stairs are approached by a protected lobby at all levels and discharge directly to outside via the lobby. On the Ground Floor it is proposed to install a fire curtain between the escape path from the stair and the main reception area as indicated in Figure 2 to create this protected lobby should a fire occur in reception. The fire curtain will operate off smoke detection in reception with fusible link as back up. Override to raise curtain will be on the stair side.

Figure 2 – Fire separation of reception area Although the office space on each level is provided with minimum 2 routes of escape, one of the 3 exits at Ground Floor level opens in the opposite direction to the direction of escape (exit facing public highway). As the area in front of this exit would not accommodate 60m persons and given the layout most occupants would use the middle exit IFC does not regard a queuing issue as likely and the exit can open inwards. With an 800mm exit provided to each exit on each floor, this would allow for 139 occupants to escape on each level based on an exit capacity of 3.6mm/person, which would be more than adequate based on the expected occupancy levels. The rear secondary stair discharges at basement level to outside, which necessitates occupants passing along a route along the outer façade of the building and re-entering into the main stair in order to reach Ground Floor and exit the building. This is an unconventional method of escape, which involves passing within 1.8m of glazed sections of the outer façade (SME unit). As such these sections of glazing must achieve 30 minutes fire resistance for integrity and insulation and the glazing must be non-openable. This is illustrated in Figure 3. The main office glazing is within 3m of the escape path and whilst it does not need to be fire resistant for escape purposes (as over 1.8m away), it cannot be used for smoke ventilation measures. The two doors shown facing the courtyard must automatically close on alarm.

Fire curtain minimum 1.8m from escape path as integrity only



Figure 3 – Escape route from rear stair

In terms of vertical egress, both stairs have a thread width of approximately 1200mm, which would allow for 873 occupants over 4 floors, way in excess of the expected maximum occupancy of these floors. Note that it is not proposed to discount an exit from each floor in this instance due to the presence of protected lobbies separating the office space from the stair on each level.

4.1.2 Smoke ventilation of common stairs

A 1.0m² automatically opening vent is provided at high level within each stair, which should have an override switch for use by the FRS, these should activate upon detection of smoke within the stair or associated lobby.

4.1.3 General Requirements

Any fire doors that are to be held open should be linked to fire detection both sides of the door. In the event of an activation of one of these detectors the door will be released so that it closes automatically, maintaining the fire protection and smoke separation.

In the event of a power failure any held open doors should fail safe closed.

Doors should be readily openable for people evacuating the building. Secure access doors will need a simple opening mechanism (handle or push bar) or a green break glass override on the escape side of the door. Powered door security devices (e.g. mag locks) should fail safe unlocked in the event of mains power failure.

All common access escape routes and staircases should be adequately lit and be provided with emergency escape lighting. The emergency escape lighting should comply with BS5266: Emergency lighting: Parts 1-7.



Signage in the common access areas should be installed to BS5499 - Part 4: 20132. The colours and style of the signage in the common areas can be agreed with Building Control so that it may be more architecturally sensitive and sympathetic to the surroundings.

4.2 Life Safety Power Supply

Two power supplies are required for the following:

Automatic smoke vents

Automatic detection and alarm system

Emergency lighting

Automatic fire curtains (unless gravity failsafe)

For AFD and emergency lighting a secondary supply is usually achieved by integral batteries as part of each unit.

The automatic smoke vents should operate even in mains power failure conditions. This may be possible with battery units, or by providing a separate power supply from a dedicated life safety switchboard. This latter should be protected from the effects of fire and routed separately from the main power supply.

4.3 Disabled egress

Disabled refuges should be provided and compliant with the relevant recommendations of the BS9999 which includes a space of 1400mm by 900mm and clear of the escape path which should be clearly identified by appropriate signage complying with BS 5499.

Two-way communication points will be required in the refuge areas, reporting back to the main reception level or relevant building entry point (i.e. fire alarm panel location) where the evacuation can be organised by attending staff. The refuge voice communication system should be designed to BS 5839 Part 93.

Escape routes should be free from any feature that might impede movement, such as unsuitable door ironmongery or raised thresholds or steps between changes of level within a storey. Any location on an escape route with a significant change in level should be provided with a refuge at a point prior to the level change.

Staff and management should implement procedures for identifying people with disabilities which may affect their ability to evacuate, and ensure that they are provided with adequate guidance for action in the event of an emergency.

A personal emergency egress plan (PEEP) should be established by the management for any disabled employees or visitors. This is likely to include training for staff in procedures and carrying operations when necessary.

The Fire Safety Management Plan to be developed by the building management should document the disabled evacuation procedures in more detail and does not form part of this Fire Safety Strategy, which deals with design criteria only.

2 BS 5499-4:2013, Code of practice for escape route signing. 3 BS 5839-9:2011, Fire detection and fire alarm systems for buildings - Code of practice for the design, installation, commissioning and maintenance of emergency voice communication systems.



In buildings without the benefit of evacuation lifts it is recommended that the provision of disabled “evac chairs” or similar aids are considered to provide the capability of evacuating mobility impaired disabled people down (or up) stairs when necessary.



5. EGRESS VIA REAR STAIR As previously mentioned, it is necessary to demonstrate that occupants can escape in relative safety despite having to pass through the basement lobby of the main stair in order to escape. The lobby doors are self-closing fire doors to the office and basement occupants would have already been expected to have passed through the lobby before occupants of the rear stair reach it so doors would be closed, and certainly even with them open as occupants escape from the office would not be subject to smoke in such a small timeframe.

Based on the occupancy numbers, exit width provision and travel distances an approximate evacuation time can be estimated. This is based on guidance of the British Standards BS 9999 (as above) and BS 7974 PD64.

Safe evacuation can be broken down into two elements; the time it takes people to escape and the time it takes for the building to become untenable.

These are called RSET (Required Safe Evacuation Time) and ASET (Available Safe Evacuation Time). The RSET includes time for the fire alarm to sound, time for people to respond to the alarm and time for them to move to a final exit from the building. The ASET is based on the fire size and smoke spread and should always be greater than the RSET. In the common areas of the building comprehensive L3 automatic fire detection and alarm is proposed. This, in combination with manual alarm call points, will provide early warning to the building occupants of a fire. It is proposed that the detectors or call points will be activated within one minute of a significant fire ignition. The alarm will immediately sound throughout the building on detection of fire. The methodology adopted for calculating the RSET in the evacuation analysis reported here follows that described within PD 7974-6 [C4]. The basic formula for determining the escape time RSET is

Where;

Time required to evacuate to a designated place of safety

Time from ignition to detection

Time between detection and alarm activation

Pre-movement time

Travel time to the designated place of safety

4 BS 7974-6:2004, The application of fire safety engineering principles to fire safety design of buildings – Part 6: Human factors: life safety strategies – occupant evacuation, behaviour and condition (sub-system 6).

travpreaRSET ttttt det

RSETt

dett

at

pret

travt



Fires take time to grow to a level where they become untenable. In general terms for a building where occupants are awake and familiar a t-squared fire would be regarded as a hazard (a smouldering fire would not). A medium t-squared fire in a room with ceiling no more than 3m would have a smoke detector operate when 10KW heat release is achieved (circa 30 seconds for medium t-squared typical of office fire loads).

IFC therefore propose detection time of 30 seconds and alarm time as zero (as automatic system). Table C.1 of PD6 takes pre-movement time as 60 seconds for the first occupant and a further 120 seconds for the last occupant. This presumes a M2 category of management which is reasonable presumption. PD6 identifies various travel speeds, both horizontally and vertically but none are for disabled persons (there is no UK fire code identifying such speeds). The average horizontal travel speed is 1.2m/s and for a female the speed reduces to 0.8m/s. It is noted UK Government assesses some disability benefit if persons cannot exceed 0.67m/s. Worse case vertical in PD6 is 0.6m/s for a woman over 50. There is little analysis on evacuation chair speeds however reference is made to a study on a 10 storey building (A) using trained staff and assuming female as worse case fire warden is taken as 0.42m/s. Travel time is taken as 0.67m/s horizontally and 0.42m/s vertically. Taking 4th floor as worse case horizontal travel distance to the stair is 24m presuming other horizontal exit discounted, giving 40 seconds and a further 40 seconds to re-enter the front stair at basement level.

Vertical distance is taken as 6m per storey therefore 30m in total or 71 seconds. The gives RSET of 30 + 0 + 180 + 151 = 361 seconds The RSET figure is for the last person i.e. 100th percentile and others will have evacuated earlier. The ASET would require smoke to enter the basement lobby and therefore provide more unsatisfactory conditions than within a stair. As the smoke filling from a basement fire would be worst case with only the stair void to allow smoke to the Ground Floor, we will investigate as to when smoke reaches the top of the door i.e. 2.1m above floor level and then where the smoke layer is at the RSET. The ASET is calculated as follows by analysing the smoke filling time and smoke temperature using CFAST (computer zone model) and determining the time it takes the smoke layer to reach the head of the door (as no leakage around the door into the lobby is expected prior to this point) and the temperature to confirm when below door height whether it will be forced passed the cold smoke seal.



The Basement and Ground Floor are taken as a single compartment with a 10m2 void linking the two levels where the accommodation stair is located. No account is taken of the smoke vents at Ground Floor as they are for fire service use and presumed closed. A sensitivity analysis includes some vents (1 door open & 2 doors open at Ground Floor) to show whether this impacts on smoke layer location and temperature in comparison with no vent model. A medium t2 fire is presumed to run 361 seconds at 290Kw/m2 as per BS7974 PD1. The smoke layer reaches 2.1m from Basement floor level after 180-190 seconds when no vents are considered. The temperature in the smoke layer at this time is 310C. At 361 seconds the smoke layer is 1.3m above Basement floor level and 660C (31oC below 1.3m – 2 zone model details upper and lower layers only) Once smoke temperature reaches 2000C the intumescent strip would have activated (between 110-2000C depending upon intumescent type) and smoke leakage would be inconsequential for duration of door integrity. It can be seen during the RSET the smoke temperature slightly exceeds the PD6 tenability limit of 600C on the office side (66oC) where occupants have to walk through smoke. However as a zone model this will be underneath the ceiling as the lower zone (of the two zone model) is at 310C. Therefore we would not expect below 2.1m to be above 600C. Once the smoke layer is below 2.1m the maximum smoke leakage would be 3m3/m/hr at 25Pa as per BS476 Part 31.1. However given the air flow at 25Pa in the test is to replicate smoke at 2000C we can see that the leakage rate would be much lower than an S rated door maximum allows. For an S rated 1600mm wide doorset the maximum smoke leakage would be 0.004m3/s with neutral pressure plane one third from floor level as per BS476 Part 22. With a 1m2 AOV in the lobby the extract potential can be determined taking the AOV acting as extract and inlet with neutral pressure plane at one third (as per a 1.5m2 external wall vent in an apartment building). An in-house spreadsheet below considers the vent as a simple shaft calculating extract and inlet rates from the temperature differential between smoke and ambient. The higher the smoke temperature the greater the extract rate through the vent. Smoke at 250C is taken as a practical worse case given the smoke temperature in the room (temperature reduction will occur as it passes around door and mixes with ambient air in top half of lobby). Ambient is taken at 200C. The CFAST model shows Ground Floor smoke layer does not exceed 1000C during the RSET. Note the actual model was run for 400 seconds and no adverse issues found.



If we assume the smoke temperature is only 250C the extract potential is 0.1m3/s which is greater than the leakage rate. At 600C the extract rate would increase to 0.3m3/s. Therefore we would not expect the lobby to be untenable during the RSET period. On this basis we can state the ASET is greater than the RSET.

Calculation of flows etc for vertical shaft with opening at top and bottom, and maintained temperature differential

See Enclosure Fire Dynamics by Karlsson & Quintiere, CRC Press, 2000

R 287 J / (kg K)

273 K

patmos 1.01E+05 Pa

g 9.81E+00 m s-2

Cd 6.00E-01 - Flow coefficient

Height 1 m Shaft height

Atop 0.67 m2 Top vent geomteric free area (ideally rectangular with dimensions small compared to Height)

Abot 0.33 m2 Bottom vent geomteric free area (ideally rectangular with dimensions small compared to Height)

Tin 25 C 298 K Internal teperature

Tout 20 C 293 K External (ambinet) temperature

rhoin 1.1809274 kg m-3 Internal density

rhoout 1.2010798 kg m-3 External (ambient) density

hnpl 0.8020965 m Neutral pressure plane height

Dptop 0.0391244 Pa Pressure differential at top vent

Dpbot -0.1585701 Pa Pressure differential at bottom vent

utop 0.2574112 m s-1 Flow speed at top vent

ubot -0.5138539 m s-1 Flow speed at bottom vent

Mtop 1.22E-01 kg s-1

Mass flow rate at top vent

Mbot -1.22E-01 kg s-1

Mass flow rate at bottom vent

Qtop 1.03E-01 m3 s-1 Volumetric flow rate at top vent

Qbot -1.02E-01 m3 s-1 Volumetric flow rate at bottom vent



6. INTERNAL FIRE SPREAD (LININGS)

The walls and ceiling linings of an enclosure such as a room can have a dramatic effect on the development of a fire and, in particular, the time it takes for the room to become completely involved.

BS 9999 suggests that wall and ceiling linings should have a minimum classification reproduced in Table 4 below, when evaluated by the methods described in BS476: Parts 65 and 76 as appropriate.

Location National

Class A)

European

Class B), C)

Small room of area not exceeding 30m2 Class 3 D-s3, d2

Other rooms Class 1 C-s3, d2

Other circulation spaces Class 0 B-s3, d2

Table 4 – Classification of Linings

NOTE Linings which can be effectively tested for “surface spread of flame” are rated for performance by reference to the method specified in BS 476-7:1987, under which materials or products are classified 1, 2, 3 or 4, with Class 1 being the highest.

(A) The National classifications do not automatically equate with the equivalent classifications in the European column, therefore products cannot typically assume a European class, unless they have been tested accordingly.

(B) When a classification includes “s3, d2”, this mean that there is no limit set for smoke production and/or flaming droplets/particles.

(C) Large rooms such as open plan offices, shops display areas need not be regarded as circulation spaces even though there are circulation routes in them.

In this table, Class 0 is better than Class 1. It is not identified in any BS test standard. A Class 0 product is either:

Composed throughout of materials of limited combustibility; or

A material having a Class 1 surface spread of flame and which has a fire propagation index (I) of not more than 12 and a sub-index (i1) of not more than 6.

The fire propagation index is established by reference to the method specified in BS 476-6. And European classifications are described in BS EN 13501-17. Parts of walls may be of a lower class than above provided that the total area in any one room does not exceed half of the floor area, up to a maximum of 60m2 in non-residential accommodation.

5 BS 476-6:1989+A1:2009, Fire tests on building materials and structures. Method of test for fire propagation for products. 6 BS 476-7:1997, Fire tests on building materials and structures Method of test to determine the classification of the surface spread of flame of products. 7 BS EN 13501-1:2007+A1:2009, Fire classification of construction products and building elements Classification using test data from reaction to fire tests.



7. INTERNAL FIRE SPEAD (STRUCTURE) It is important that the structure and key construction elements of a building remain fully functional for a reasonable period of time during a fire. It is obviously beneficial if these elements remain in a serviceable condition after the fire for ease of reinstatement. In addition, a fire should be contained by fire resisting elements of the building to prevent it spreading to other parts of the building. This containment should include voids and cavities that could provide a path for fire. All elements of structure should be given the period of fire resistance in respect of the criteria of loadbearing capacity, integrity and insulation when evaluated in accordance with the appropriate part of BS476: Parts 218 or 229:1987 as suggested in Tables 24 and

25 of BS 9999. The effects of these recommendations on the structure are discussed in this chapter.

In the absence of any detail design, the following recommendations are generic in nature and are intended to provide the design team with guidance in the design and specification of the fire resisting elements. In particular it should be noted that much of the guidance assumes traditional methods of construction will be used, which may not be the case. It is recommended that IFC reviews the details once they are produced and the fire safety strategy updated accordingly.

7.1 Structural Fire Resistance

The top floor of the block falls within the “above 5m, not more than 18m” category. This recommends that elements of structure are provided with at least 60 minutes fire resistance, including floor slabs. The basement will also require 60 minutes fire resistance.

7.2 Compartmentation

The floors would not ordinarily be required to be compartment floors, although it is recommended in this instance that they form compartment floors (apart from the floor separating the basement and Ground Floor due to the open stair connecting the two), for the purposes of reducing the risk of external fire spread, which will be assessed in greater detail later in the report. On this basis they should be provided with 60 minutes fire resistance. Since floors typically form elements of structure to a building they would ordinarily require fire rating regardless.

Any service penetrations between compartments are to be contained within protected shaft(s) requiring a minimum of 60 minutes fire resistance.

Both stair shafts should be enclosed in 60 minutes fire resisting construction with FD30S doorsets. The lobbies serving the stair on each floor level will require 30 minutes fire resistance again with FD30S doorsets, while the Ground Floor lobby/reception will require 60 minutes resistance since it forms an extension of the stair to the final exit. As previously noted this should incorporate a 60 minute rated fire curtain to separate the main reception area from the escape path from the stair.

8 BS 476-21:1987, fire tests on building materials and structures, methods for determination of the fire resistance of loadbearing elements of construction. 9 BS 476-22:1987, Methods for determination of the fire resistance of non-loadbearing elements of construction.



It should be noted that a fire-fighting lobby is required from the office accommodation to the main stair and as such should be enclosed in 120 minutes fire resisting construction with FD30S doorsets required to the stair and FD60S doorsets required to the lobby itself. This applies to Basement and Ground Floor only. Where compartment floors and party walls meet the external wall, fire barriers with the equivalent fire resistance of the floor or wall (60 minutes in this instance) should be provided to fill any void between the external façade and the floor or wall.

The plant room, store rooms and kitchenette will require 30 minutes fire resistance enclosure with FD30 doorsets. The dry waste room will also require 30 minutes fire resisting enclosure, with FD30S doorset since it enters into the stair lobby.

All protected lobbies to stairs require 30 minutes fire resisting enclosure with FD30S doorsets (except for the aforementioned fire-fighting lobby to the main stair). Shafts and service risers passing through the floor slab will need to be constructed to prevent fire spread and should therefore provide 60 minutes fire resistance enclosure plus FD30 doorsets.

In the event of a power failure any held open doors should fail safe closed.

The building external wall should be fire resistant to a 60 minute standard (60 minutes integrity and 15 minutes insulation) other than the area of non-load bearing façade permitted to be unprotected in accordance with BR18710. This is discussed further in the next section of the report.

7.3 Penetration and Linear Gap Seals

All pipes, ductwork and services passing through fire-resisting barriers should be penetration sealed with an appropriate sealing system and/or fire damper which has been shown by an appropriate test or assessment to maintain the period of the fire-resistance of the barrier. The penetration sealing system should be designed and installed in accordance with the recommendations contained within The IFSA Code: Sealing Apertures and Service Penetrations to Maintain Fire Resistance.

7.4 Cavity Fire Barriers

Compartment walls/floors are to maintain their integrity where meeting an external wall and this may include the provision of a cavity fire barrier inside the external wall cavity giving 60 minutes fire resistance. Where a cavity wall as described in ADB Diagram 34 is proposed, cavity barriers only require 30 minutes fire resistance, but must also be installed around window openings and other external wall penetrations.

Concealed cavities i.e. the void between a suspended ceiling and the soffit of the floor above, or raised floors that are used for services etc., will require cavity barriers typically installed so as to observe a 20 metre maximum linear dimension.

10 BR187:1991, External fire spread, building separation and boundary distances.



There will be a 50mm void between the rc composite slab and the plasterboard ceiling. Provided the timber battens supporting the plasterboard are minimum 38mm wide they are sufficient for cavity barrier purposes.

7.5 Third Party Certification

Any fire and smoke control assemblies should be provided with an appropriate certificate from a recognised third party accreditation body, such as IFC Certification Ltd, in order to demonstrate compliance with Clause 0.15 of Volume 2 of Approved Document B and Regulation 16B of the Building Regulations 2010. Assessment and test evidence should also be available for inspection by the approving authorities and other interested parties.

7.6 Cables

Cabling for fire safety systems is to comply with Table 1 of BS851911.

11 BS 8519:2010, Selection and installation of fire-resistant power and control cable systems for life safety and fire-fighting application – Code of practice.



8. EXTERNAL FIRE SPREAD

8.1 Building Separation and Boundary Distances

When a building is burning, heat will radiate through non fire-resisting openings in the external walls. This heat can be intense enough to cause ignition to adjoining buildings or combustible material therein. In order to reduce the chance of this occurring, the Building Regulations place limits on the area of external elevation with no fire resistance. This area is known as the ‘unprotected area’ and is affected by such factors as distance from the boundary, use of the building and compartment size.

Boundary locations are taken as the centre of a public highway, the boundary of the site or a notional boundary mid-way between buildings on the same site (as Regulation B4 is concerned with the heat flux at half the distance between buildings). And the recommended minimum boundary distance at each elevation has been assessed and based on the guidance of the BRE Report BR18712.

The external walls will provide 60 minutes fire resistance from the inside (60 minutes integrity and 15 minutes insulation), subject to the unprotected area allowance where no fire resistance is necessary.

The entire façade of the largest compartment on each elevation is used for the calculations, which would encapsulate all openings contained therein. The distance from the boundary on each elevation varies, hence the point at which the façade is closest to the boundary will be used in each case as a worst case scenario. Most elevations of the building adjoin adjacent buildings and would be compartment walls, apart from the northern elevation facing onto Old Street, and the western elevation facing onto the car park from ground level up. For the purpose of this assessment, it will only be these 2 elevations that will be assessed, and an exposed portion of the third and fourth floors of the eastern elevation which contain glazing.

8.2 External fire spread calculations

The external fire spread for the building has been calculated using the enclosing rectangles technique in BR 187, shown in.

North

elevation West

elevation

East elevation 3rd floor

East elevation 4th floor

INPUT DATA

Distance from boundary (m) 7 3 2.5 2.9

Double distance due to sprinklers? N N N N

Height of enclosing rectangle (m) 3 3 3 3

12 BRE Report BR187: External fire spread: building separation and boundary distances.



Width of enclosing rectangle (m) 14.3 27 12.5 7.7

Occupancy type B B B B

A=Residential, office and assembly & recreation

B=Shop & commercial, industrial & other non-residential

CALCULATION FACTORS

Distance from boundary for calc (m) 7 3 2.5 2.9

h/d 0.43 0.38 1.20 1.03

w/d 2.04 3.33 5.00 2.66

Larger of h/d or w/d 2.04 3.33 5.00 2.66

Below lower limits of table? N N N N

Above upper limits of table? N N N N

Factor f 0.95 0.87 0.77 0.91

RESULTS

Max. unprotected % of enc. rect. 100.0% 60% 28.5% 43.9%

Unprotected area allowed (m2) 42.9 48.6 10.7 10.1

Table 5 – External fire spread calculations

The northern elevations can have 100% unprotected area.

The current design is as per Figure 4.



Figure 4: Unprotected Area Assessment

The western elevation calculation being based on a minimum distance of 3m from the relevant boundary on First Floor and above and enclosing rectangle of 27m x 3m. This is a maximum 60% but the current design has 66% (Figure 4) and therefore additional fire resistant glazing is required per floor.

While the recessed sections of the Third and Fourth Floors of the eastern elevation can have 28.5% and 43.9% unprotected areas respectively.

The section of façade at Ground Floor and basement level (single compartment) from an enclosing rectangle 21m x 6m on the western elevation facing onto the courtyard can have 35% unprotected area. The proposed design has maximum 30% and therefore satisfactory.

The Basement level has a 60 minute fire curtain with insulated zone (puts a 10KW/m2 radiated heat limit on the unexposed side 1m from the curtain) across the recess operated via a fusible link. This is sufficient protection given the distance to the boundary.

The SME unit at basement level has fire resistant glazing to 30 minutes integrity and insulation as adjacent the escape route.



8.3 Reaction to Fire External wall surfaces should have the classification as shown below in Table 6, when evaluated by the methods described in BS476 (Fire tests on building materials and structures): Parts 6 and 7 as appropriate. The surface spread of flame classification for the external walls should be as Table 6, noting that all parts of the building are below 18m.

Building Section Performance

National Class European Class(1)(2)

Building section over 18m Class 0 B-s3, d2 or greater

Building section under 18m Index (I) not more than 20* C-s3, d2 or greater (1) The National classifications do not automatically equate with the equivalent

classifications in the European column, therefore products cannot typically assume a European class, unless they have been tested accordingly.

(2) When a classification includes “s3, d2”, this mean that there is no limit set for smoke

production and/or flaming droplets/particles. * I is the index of performance of a material when tested under BS476: Fire tests on

materials and structures: Part 6: 1981 or 1989: Method of Test for Fire Propagation of Products.

Table 6 - Classification of External Wall Surfaces

The fire propagation index is established by reference to the method specified in BS 476-6. And European classifications are described in BS EN 13501-113.

8.4 Insulation

External walls should comply as follows; “External walls should either meet the performance criteria given in BRE Report BR 13514 [N1] for cladding systems using full scale test data from BS 8414-115 or BS 8414-216, or …any cladding material, insulation product, filler material (not including gaskets, sealants and similar), etc., used in the external wall construction should be of limited combustibility.”

13 BS EN 13501-1:2007+A1:2009, Fire classification of construction products and building elements. Classification using test data from reaction to fire tests. 14 BR 135:2013, Fire performance of external thermal insulation for walls of multi-storey buildings. 15 BS 8414-1:2002, Fire performance of external cladding systems, test method for non-loadbearing external cladding systems applied to the face of the building. 16 BS 8414-2:2005, Fire performance of external cladding systems, test method for non-loadbearing external cladding systems fixed to and supported by a structural steel frame.



9. ACCESS AND FACILITIES FOR THE FIRE AND RESCUE SERVICE

9.1 Access

In order to extinguish a fire within this building it is important that the fire service can gain access onto the premises, and from there, into the building.

Fire and Rescue Service (FRS) access to the site will be via Old Street. Any dead-end section of road should be provided with a suitable turning circle or hammerhead for a fire appliance.

Roads should be suitable for a FRS pumping appliance with a 3.7m clear width and 3.7m vertical clearance height. The load bearing capacity should be a minimum of 14 tonnes.

9.2 Fire-fighting Water

A water supply, either from a public fire hydrant system or from a private fire hydrant ring main system designed to meet BS999017 is required within 90m of dry main inlets to each block giving minimum 1500l/minute.

The highest occupied storey is less than 18m; thus a fire fighting shaft is not required, although as previously noted there will be a fire-fighting lobby provided at Ground Floor level in the main stair.

A dry riser main is required within the building in the main stair, with outlets to be provided within the stair at every level including basement level. An inlet should be provided at Ground Floor level within 18m of the pump appliance parking position and visible from it.

It is understood from the FRS consultation their preference is for the dry riser outlet to be located in the main stair lobby. As the lobbies are not ventilated on each upper floor and presuming the FRS connect on the riser one or two floors below the fire floor there may be excessive air flow lost through the stair doors in comparison with the outlet being in the stair but IFC presume the FRS are aware of this potential problem and will take suitable measures during fire-fighting operations.

9.3 Smoke Ventilation

The detailed information for the smoke ventilation is covered under the Means of Escape section. All vents should be provided with override switches for FRS use and be capable of opening or closing the vents.

A fire alarm panel should be provided at fire service access level to the core, to confirm which floor the Landlord’s smoke detector/ventilation system has activated.

17 BS 9990:2006, Code of practice for non-automatic fire-fighting systems in buildings.



10. FIRE SAFETY MANAGEMENT

A Fire Risk Assessment will be required for the building, according to The Regulatory Reform (Fire Safety) Order (FSO) 2005.

It should be the responsibility of the Landlord to ensure that adequate information will always be available on fire safety procedures within the building for any operatives working in the building.



11. CONCLUSION

International Fire Consultants Ltd. are of the opinion that were the proposed building, constructed and operated in accordance with this report, it would fully comply with the requirement of Part B of the Building Regulations 2010.

It is envisaged that this document will be used as part of the Building Regulations submission in support of Regulation 38 and Part B Fire Safety and by the responsible person in the risk assessment produced by the Landlord/Management Company under the Regulatory Reform (Fire Safety) Order 2005 (FSO).

The building control body and the local fire service should be consulted as part of the Building Regulation submission.

12. LIMITATIONS

Our advice is strictly limited to the scope of our current brief, i.e. to provide a fire safety strategy report for the proposed office building at 112-116, Old Street, London.

International Fire Consultants Ltd has not reviewed any other issues within the project other than those identified in our report. We offer no comment on the adequacy or otherwise of any other aspects of the development (whether related to fire safety or any other issue) and any absence of comment on such issues should not be regarded as any form of approval. The advice should not be used for buildings other than that named in the title.

Prepared by: Checked by: Lee Morgan Angus Sangster BEng (Hons) MRICS MSFPE CFPS BEng (Hons) GIFireE

Fire Safety Engineering Manager Senior Fire Safety Engineering Manager International Fire Consultants Ltd (IFC) International Fire Consultants Ltd (IFC) References

A. Evacuation of High Rise Buildings by an Evacuation Chair; Sano, Omiya & Hagiwara, 2004



APPENDIX A

CFAST OUTPUT DATA

Figure A1 – Smoke Layer Height

Figure A2 – Model geometry

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

0.00 50.00 100.00 150.00 200.00 250.00 300.00 350.00 400.00 450.00

Laye

r H

eigh

t (m

)

Time (s)

Basement Smoke Layer Height (m)

HGT_1 Layer Height basement - no vents m HGT_1 Layer Height basement - 1 vent m

HGT_1 Layer Height basement - 2 vents m

1 vent line (red) located behind green line (2 vents)

Upper layer temperature

Fire @360s

Basement

Ground Floor

Open stair void



Area No of Vents Upper layer

temperature @360s (oc)

Lower layer temperature @ 360s

(oc)

Basement 2 62 31

1 62 31

0 66 31

Ground Floor 2 40 21

1 40 21

0 36 24

Table A1 – Layer temperatures @ RSET

Documents

FIRE SAFETY STRATEGY - Stylusdataroom.stylus.london/wp-content/uploads/2019/02/Fire-Safety-Strategy.pdfThe report is based on the drawings supplied on the 2nd November 2017 by GPad