Part of the BRE Trust

BRE FIRE CONFERENCE 2015

11th June 2015

Part of the BRE Trust

Assessing the impact on some electrical cable supports and fixings

BRE Fire Conference 201511th June 2015

Ciara Holland and Martin ShippFire Safety Team, BRE Global

Introduction to BRE

Fire investigation work at BRE

– Learning lessons from fires– performance of the building– performance of fire safety systems– behaviour of occupants– improved regulations or guidance (AD B)– Improved (or new) knowledge, information or data

for fire safety engineering. – Early warning system of topics to be addressed during

updating of documentation;– factory fires - large single-storey buildings, sandwich

panels, cladding - changes in 2000 edition of AD B– truss-rafter roofs - ODPM research programme

Fire investigation work at BRE

– BRE has well-established capability to assess the effects and implications of the fire (the “lessons learned”) – not the cause.– BRE provides FRSs and other agencies with scientific

support; experimental and/or modelling work.– Act as expert witnesses in Criminal Court, Coroner’s Court,

Sheriff's Court, Fatal Accident Enquires, etc.

– Findings feed into Building Regulations guidance and other guidance, and/or into research and/or knowledge base.

– Gratefully acknowledge assistance of Fire and Rescue Service, and other agencies. Most of our fire visits are arranged through the Fire and Rescue Service.

Major fire investigations

– Woolworths, Manchester, May 1979– Stardust Disco, Dublin, February

1981 – King's Cross, London, November

1987– Piper Alpha, July 1988– Windsor Castle, November 1992– The Channel Tunnel, November 1996– Ladbroke Grove Rail Crash, October

1999– Yarl’s Wood Detention Centre,

Bedfordshire, February 2002– Rosepark Care Home, Scotland,

January 2004– Bethnal Green, London, July 2004

– Harrow Court, Stevenage, February 2005– Colindale, London, July 2006– Monica Wills House, Bristol, December 2006– Cutty Sark, June 2007– Penhallow Hotel, Newquay, August 2007– Atherstone on Stour, Warwickshire,

November 2007– Royal Marsden Hospital, London, January

2008– Lakanal House, London, July 2009– Peckham & Camberwell Timber Frames,

London, November 2009 & January 2010– Shirley Towers, Southampton, April 2010– Freckleton House Fire, January 2012

ManchesterWoolworth’s 1979

Stardust Disco 1981

King’s Cross 1987

Windsor Castle 1992

The Channel Tunnel 1996

Major fire investigations

Lakanal House2009

Atherstone on Stour 2007

Cable supports experimental programme

Common sights at fire scenes

Common sights at fire scenes

Harrow Court – 2nd February 2005

– Two fire-fighters and one resident died.

– Fire-fighters trapped by fallen fire-alarm cable.

– Inquest in March 2007.

– HM Coroner issued several recommendations through a Rule 43 letter– One to social housing providers regarding the

support of fire alarm cables which should conform (as a minimum) to BS 5839 – Part 1 : 2002; clause 26.2 (f:)

Inquest into Harrow Court – Findings. Rule 43 Harrow Court Letter. Published by Fire Brigades Union. Available at:http://www.fbuberkshire.co.uk/wp-content/uploads/2011/01/Harrow_Court_5_Findings_Rule43_Letter.pdf. Last accessed 10th October 2013.

Harrow Court – Update to BS 5839-1

– “Methods of cable support should be non-combustibleand such that circuit integrity will not be reduced below that afforded by the cable used, and should withstand a similar temperature and duration to that of the cable, while maintaining adequate support.”

– NOTE 8 In effect, this recommendation precludes the use of plastic cable clips, cable ties or trunking, where these products are the sole means of cable support.

– NOTE 9 Experience has shown that collapse of cables, supported only by plastic cable trunking, can create a serious hazard for fire-fighters, who could become entangled in the cables.

BS 5839-1:2002+A2:2008 Fire detection and fire alarm systems for buildings. Code of practice for system design, installation, commissioning and maintenance, British Standards Institution.

Atherstone-on-Stour – 2nd November 2007

– Four fire-fighters died in a large highly-insulated warehouse fire.

– It was noted from witness statements that fire-fighters were being caught up in fallen cables during the incident.

– It is unclear whether the four fatalities were trapped by cables.

Atherstone-on-Stour – Operational Bulletin

– Warwickshire Fire and Rescue Service issued an Operational Bulletin in March 2012 (OB 12/04):

• Hanging Cable Hazards from Surface Mounted Conduit and Trunking

– Based on experimental work carried out by BRE Global for the Fire Service.

– This work confirmed that plastic conduit or trunking surface mounted on ceilings and walls may fail at relatively low temperatures (150oC).

Shirley Towers – 6th April 2010

– Two fire-fighters died.

– Trapped by fallen cables prior to an event of abnormal rapid fire development.

– Inquest in February 2013.

– HM Coroner issued recommendations in several Rule 43 letters. • Reiterated the recommendations made by HM Coroner

after the Harrow Court inquest. • Further recommendation to have “… Building

Regulations amended to ensure ALL [sic] cables, not just fire alarm cables, are supported by fire-resistant cable supports”.

• Recommended an “amendment to BS 7671 (2008)…” to achieve this.

Aims and objectives

Aims and objectives

1. To assess the ability of a selection of commercially available cable supports for electrical installations to: • maintain their integrity and, • hold electrical cabling in place when exposed to temperatures typically encountered

in compartment fires.

2. To assess the performance of a range of commercially available fixings for cable supports in concrete substrates when exposed to elevated temperatures.

3. Findings to inform Government.

Methodology

Experimental rig

BS 476-33:1993, ISO 9705:1993

Experimental rig – instrumentation

Supports in-situ

Experimental setup

– Standard 1.5mm flat twin and earth PVC sheathed cable

– Five types cable supports or clips

– Fixed with zinc-plated hardened steel 7 x 1¼ inch twinthread wood screws

– To fix into concrete lintels used same screws and plastic plugs

– Five supports of each type per lintel at 300 mm spacings

Cable supports experiments

– Experiment 1– 0.7 MW wood crib

– Experiment 2– 1.3 MW wood crib

– Heat release rate was not measured

– Wooden cribs chosen as follows a more “typical” fire growth curve than liquid pool fire

Results and findings

Results Experiment 1

Lintel TypeAverage

maximum temperature at lintel (°C)

Average temperature when cable observed to

drop (°C)

Support 1

Support 2

Support 3

Support 4

Clip 5

1 Timber 264 258 All intact All intact All intact All intact 4 failed

2 Concrete 294 286 All intact All intact All intact All intact Allfailed

3 Timber 255 243 All intact All intact All intact All intact Allfailed

4 Concrete 204 No drop All intact All intact All intact All intact 4 failed

Photos after Experiment 1

Close up of Lintel 1

Results Experiment 2

Lintel TypeAverage

maximum temperature at lintel (°C)

Average temperature when cable observed to

drop (°C)

Support 1

Support 2

Support 3

Support 4

Clip 5

1 Timber 578 481 All intact All intact All intact All intact All failed

2 Concrete 557212 (Clip 5) and 221(Clip

2)Three failed *

Three failed *

Three failed *

Three failed * All failed

3 Timber 570 486 All intact All intact All intact All intact All failed

4 Concrete 388 310 All intact All intact All intact All intact All failed

*Due to fixing failure and not support

Photos after Experiment 2

Close up of Lintel 2

Concrete lintel after Experiment 2

Fixings experiment

Number DetailFixing 1 Countersunk 6 mm x 45 mm concrete screw

Fixing 2 Multipurpose twin thread countersunk zinc plated 4 mm x 40mm screw with 5 mm lightweight plastic wall plug

Fixing 3 Hammer-in fixing 6 mm x 40 mm; nylon plug with drive screw

Fixing 4 Multipurpose twin thread countersunk zinc plated 4 mm x 40mm screw with 6 mm medium weight nylon wall plug

Fixing 5 Sleeve anchor M6 x 40 mm medium weight use

– Standard aerated 3.6N concrete blocks of dimensions 440mm by 215mm by 100mm deep.

– Each block was placed horizontally into an oven on top of two other concrete blocks (placed vertically) as supports to allow for the suspension of weights from the fixings.

– Steel bolts were used as weights, attached to the fixings using steel wire.

Fixings before installation

1

2

3

4

5

Exemplar block with fixings before experiment

Oven arrangement

Results from Fixings experiments

Oven temperature

(°C)

Maximum temperature in block (°C)

Condition of each fixing

Fixing 1 Fixing 2 Fixing 3 Fixing 4 Fixing 5

100 58 Intact Intact Intact Intact Intact200 104 Intact Intact Intact Intact Intact

300 100 Intact Weakened Intact Intact Intact

400 109 Intact Weakened Weakened Failed Intact

Block after exposure to 400oC

Conclusions and recommendations

Conclusions

– Quite simple and readily available supports and fixings capable of withstanding temperatures greater than 600oC can be sufficient to avoid cables falling when exposed to typical compartment fires.

Implications for regulations and/or policy

– Electrical Safety First issued a proposal to the British Standards committee to amend BS 7671:2008 (2011) to address cable entanglement issues in fire escapes.

– BS 7671:2008 + A3:2015 (IET Wiring Regulations 17th

Edition) was published in January 2015 and will come into effect in July 2015.

– Among several other amendments; a new regulation (Regulation 521.11.201) was included. The findings of this research informed this new regulation during the consultation process.

BS 7671 New regulation

– 521.11.201 Wiring systems in escape routes shall be supported such that they will not be liable to premature collapse in the event of fire. The requirements of Regulation 422.2.1 shall also apply, irrespective of the classification of the conditions for evacuation in an emergency.

– NOTE 1: Non-metallic cable trunking or other non-metallic means of support can fail when subject to either direct flame or hot products of combustion. This may lead to wiring systems hanging across access or egress routes such that they hinder evacuation and firefighting activities.

BS 7671 – New regulation cont’d

– NOTE 2: This precludes the use of non-metallic cable clips, cable ties or trunking as the sole means of support. For example, where non-metallic trunking is used, a suitable fire-resistant means of support/retention must be provided to prevent cables falling out in the event of fire.

BRE recommendations

– The findings of the cable supports experiments supported the above amendments.

– During consultation we proposed that it is worth considering:

– The inclusion of fixings as well as supports for cables in NOTE 1 and NOTE 2 to make clear that non-metallic fixings can fail when subject to elevated temperatures.

– The inclusion of support for non-metallic conduit as well as the non-metallic trunking discussed in NOTE 2.

Thank you

Martin Shipp and Ciara Holland

Fire Investigation Team, BRE Global

T: +44 (0) 1923 665286

M: +44 (0) 78 90256154

F: +44 (0) 1923 664910

E: hollandcm@bre.co.uk

W: www.breglobal.com/fire

BRE Global, Garston, Watford WD25 9XX, UK

Part of the BRE Trust

BRE FIRE CONFERENCE 2015

Thank you

www.bre.co.uk/fire @brewatford #brefireconf