Engineering

Firefighter Safety & Solar Photovoltaic Panels On Buildings ??

2016-09-14:  Only now are we really catching up with the extremely serious matter of Fire Safety in Sustainable Buildings … serious for building occupants … and firefighters !

‘ In order to achieve sustainable development, environmental protection and energy efficiency/conservation shall constitute integral parts of the development process, and shall not be considered in isolation.’

2016 Dublin Code of Ethics: Design, Engineering, Construction & Operation of a Safe, Resilient & Sustainable Built Environment for All   ( www.sfe-fire.eu )

The Performance Target for New Construction must be Positive Energy Buildings.

So … we will see more and more Solar Photovoltaic Panels installed on more and more buildings … in every country.  Certainly not less !   And, let’s face it, many will not be properly approved, i.e. shown to be ‘fit for their intended use’ …

Colour photograph showing a house fire caused by Solar Photovoltaic Roof Panels.

Colour photograph showing a house fire caused by Solar Photovoltaic Roof Panels.

At the beginning of this decade, a Fire Research Project was carried out by the Underwriters Laboratories Firefighter Research Institute in the USA … and it addressed the issue of firefighter vulnerability to electrical hazards, and serious injury, when fighting a fire involving Solar Photovoltaic (PV) Modules and Support Systems installed on buildings.

Colour photograph showing two firefighters on a roof, one with cutting equipment. Solar Photovoltaic Roof Panels restrict firefighter access to building interior roof spaces.

Colour photograph showing two firefighters on a roof, one with cutting equipment. Solar Photovoltaic Roof Panels restrict firefighter access to building interior roof spaces.

The Total Global Solar Energy Capacity averaged 40 % annual growth from 2000 to 2010 (source: International Energy Agency).  In the USA, Grid-Connected Solar Photovoltaic Capacity grew 50 % per year for much of that time (source: US Federal Energy Regulatory Commission).  These trends increase the potential of a Fire Service Response to a building having a Photovoltaic Installation, irrespective of the PV being involved with the initiation of the fire event.  As a result, conventional firefighter tactics for suppression, ventilation and overhaul have been complicated, leaving firefighters vulnerable to potentially unrecognized exposure.  Though the electrical and fire hazards associated with electrical generation and distribution systems are well known, PV Systems present unique safety concerns.  A limited body of knowledge and insufficient data exist to understand these risks … to the extent that Fire Services have been unable to develop safety solutions and respond in a safe manner.

This Fire Research Project developed the empirical data needed to quantify the hazards associated with PV Installations … and provided the foundation to modify current or develop new firefighting practices to reduce firefighter deaths and injury.

Colour photograph showing a large array of Solar Photovoltaic Panels on a roof. Extra loading on roof structures must be considered, as well as possible interference with roof fire evacuation routes for able-bodied occupants.

Colour photograph showing a large array of Solar Photovoltaic Panels on a roof. Extra loading on roof structures must be considered, as well as possible interference with roof fire evacuation routes for able-bodied occupants.

The Tactical Considerations addressed during the Project include:

  • Shock hazard due to the presence of water and PV power during fire suppression activities ;
  • Shock hazard due to the direct contact with energized components during firefighting operations ;
  • Emergency disconnect and disruption techniques ;
  • Severing of conductors ;
  • Assessment of PV power during low ambient light, artificial light and light from a fire ;
  • Assessment of potential shock hazard from damaged PV Modules and Systems.

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Office of California’s State Fire Marshal – November 2010

Fire Operations for Photovoltaic Emergencies (CAL FIRE – 2010)  (PDF File, 1.99MB)

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UL Report (2011):  The Following Summarizes the Findings of This Fire Research Project:

  1. The electric shock hazard due to the application of water is dependent on voltage, water conductivity, distance and spray pattern.  A slight adjustment from a solid fire hose stream towards a fog pattern (10 degree cone angle) reduced measured current below perception level.  Salt water should not be used on live electrical equipment.  A distance of 6 m has been determined to reduce potential shock hazard from a 1000 VDC source to a level below 2 mA, considered as safe.  It should be noted that pooled water or foam may become energized due to damage in the PV System.
  1. Outdoor weather exposure-rated electrical enclosures are not resistant to water penetration by fire hose streams.  A typical enclosure will collect water and present an electrical hazard.
  1. Firefighters’ gloves and boots afford limited protection against electrical shock provided the insulating surface is intact and dry.  They should not be considered equivalent to Electrical Personal Protective Equipment (PPE).
  1. Turning off an array is not as simple as opening a disconnect switch.  Depending on the individual system, there may be multiple circuits wired together to a common point such as a combiner box.  All circuits supplying power to this point must be interrupted to partially de-energize the system.  As long as the array is illuminated, parts of the system will remain energized.  Unlike a typical electrical or gas utility … on a PV Array, there is no single point of disconnect.
  1. Tarps offer varying degrees of effectiveness to interrupt the generation of power from a PV Array, independent of cost.  Heavy, densely woven fabric and dark plastic films reduce the power from PV to nearly zero.  As a general guide, if light can be seen through a tarp, it should not be used.  Caution should be exercised during the deployment of tarps on damaged equipment, as a wet tarp may become energized and conduct hazardous current if it contacts live equipment.  Also, firefighting foam should not be relied upon to block light.
  1. When illuminated by artificial light sources, such as Fire Department light trucks or an exposure fire, PV Systems are capable of producing electrical power sufficient to cause a lock-on hazard.
  1. Severely damaged PV Arrays are capable of producing hazardous conditions ranging from perception to electrocution.  Damage to the array may result in the creation of new and unexpected circuit paths.  These paths may include both array components (module frame, mounting racks, conduits, etc) and building components (metal roofs, flashings and gutters).  Care must be exercised during all operations, both interior and exterior.  Contacting a local professional PV Installation Company should be considered to mitigate potential hazards.
  1. Damage to modules from tools may result in both electrical and fire hazards.  The hazard may occur at the point of damage or at other locations depending on the electrical path. Metal roofs present unique challenges in that the surface is conductive unlike other types such as shingle, ballasted or single ply.
  1. Severing of conductors in both metal and plastic conduit results in electrical and fire hazards.  Care must be exercised during ventilation and overhaul.
  1. Responding personnel must stay away from the roofline in the event of modules or sections of an array sliding off the roof.
  1. Fires under an array but above the roof may breach roofing materials and decking … allowing fire to propagate into the attic space of the building.

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NIST WTC Recommendations 29-30 > Improved Fire Education

Previous Posts in This Series …

2011-10-25:  NIST’s Recommendations on the 9-11 WTC Building Collapses … GROUP 1. Increased Structural Integrity – Recommendations 1, 2 & 3 (out of 30)

2011-11-18:  NIST WTC Recommendations 4-7 > Structural Fire EnduranceGROUP 2.  Enhanced Fire Endurance of Structures – Recommendations 4, 5, 6 & 7

2011-11-24:  NIST WTC Recommendations 8-11 > New Design of StructuresGROUP 3.  New Methods for Fire Resisting Design of Structures – Recommendations 8, 9, 10 & 11

2011-11-25:  NIST WTC Recommendations 12-15 > Improved Active ProtectionGROUP 4.  Improved Active Fire Protection – Recommendations 12, 13, 14 & 15

2011-11-30:  NIST Recommendations 16-20 > Improved People EvacuationGROUP 5.  Improved Building Evacuation – Recommendations 16, 17, 18, 19 & 20

2011-12-04:  NIST WTC Recommendations 21-24 > Improved FirefightingGROUP 6.  Improved Emergency Response – Recommendations 21, 22, 23 & 24

2011-12-07:  NIST WTC Recommendations 25-28 > Improved PracticesGROUP 7.  Improved Procedures and Practices – Recommendations 25, 26, 27 & 28

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2011-12-08:  SOME PRELIMINARY COMMENTS …

  1.     At last, we arrive at the Group 8 Recommendations !   At this stage … my impression is that the NIST Team began to run out of steam, because these two short Recommendations barely scratch the surface with regard to the significant education and training needs of the many different design, construction, management, operation, maintenance and emergency response disciplines engaged with, and confronted by, the Built Environment … every day of every week.

After a careful reading of all 30 NIST WTC Recommendations, I hope that you have satisfied yourself/yourselves that these Recommendations must be applied to ALL Buildings … not just Tall Buildings.  At various times … Iconic Buildings, and Buildings having a Critical Function or an Innovative Design have been specifically mentioned.  And look back to Recommendation 22a … tunnels and subways also made an appearance !   The proper focus for the International Fire Science and Engineering Community must be on the Built Environment as a whole.

At All Levels in a Typical Construction Project … there are also pressing education and training needs.  It is of little use if the Project Design Documentation is 100% … and the people actually installing the passive fire protection measures or the active fire protection systems on site don’t know which end is ‘up’ !   The Project Design Documentation, in whatever format, is merely a means to an end … a fully realized and occupied Building, which is fire-safe.

Preferably … we should be discussing the mandatory Re-education and Re-training of Practitioners in the different Disciplines … [CPD (Continuing Professional/Personal Development) is not at all sufficient !] … accompanied by a very necessary Re-engineering of the Stakeholder Professional and Educational Institutions … and other related Organizations, particularly National Authorities Having Jurisdiction (AHJ’s).

Our Best Hope for Transformation … lies with the current crop of third-level undergraduate students in the different disciplines.  And, as we are discovering with the introduction of the Structural EuroCodes in the European Union, it will take perhaps 5-8 years of continuous student output to transform pre-9/11 conventional fire engineering … into a post-9/11 and post-Mumbai fire engineering which is properly ‘reliability-based’ and ‘person-centred’, i.e. Sustainable Fire Engineering !

As for the Future, and Some Conclusions to this Series … coming shortly to a computer monitor screen near you !

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2005 NIST WTC RECOMMENDATIONS

GROUP 8.  Education and Training

The professional skills of building and fire safety professionals should be upgraded through a national education and training effort for fire protection engineers, structural engineers, and architects.  The skills of building regulatory and fire service personnel should also be upgraded to provide sufficient understanding and the necessary skills to conduct the review, inspection, and approval tasks for which they are responsible.

NIST WTC Recommendation 29.

NIST recommends that continuing education curricula be developed, and programmes be implemented for:  (1) training fire protection engineers and architects in structural engineering principles and design;  and (2) training structural engineers, architects, fire protection engineers, and code enforcement officials in modern fire protection principles and technologies, including the fire resisting design of structures;  and (3) training building regulatory and fire service personnel to upgrade their understanding and skills to conduct the review, inspection, and approval tasks for which they are responsible.  The outcome would further the integration of the disciplines in effective fire-safe design of buildings.  Affected Organizations:  AIA, SFPE, ASCE, ASME, AISC, ACI, and state licensing boards.  Model Building Codes:  Detailed criteria and requirements should be incorporated into the model building codes under the topic ‘Design Professional in Responsible Charge’.

NIST WTC Recommendation 30.

NIST recommends that academic, professional short-course, and web-based training materials in the use of computational fire dynamics and thermo-structural analysis tools be developed and delivered to strengthen the base of available technical capabilities and human resources.  Affected Organizations:  AIA, SFPE, ASCE, ASME, AISC, ACI, ICC, and NFPA.

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Architectural & Structural Engineering Design for Robustness !

2009-07-11:  Earlier in the year … a certain non-native English speaking colleague of mine, who is very active in European and International standardization work (and has very good English !), had never heard of the word ‘robust’.  She just could not get her head around either the word or the concept … and thought I was making it all up !

Fast forward a few months … and as a long-time member of the International Association for Bridge & Structural Engineering (IABSE), an occasional ‘freebie’ lands on my desk.  This one was a real treat !

Published by IABSE in Switzerland … Structural Engineering Document #11: Design for Robustness … was written, in language accessible to both structural engineers and architects alike, by Franz Knoll and Thomas Vogel.

The objective of these Structural Engineering Documents is to provide in-depth information to practicing architects and structural engineers, in reports of high scientific and technical standards, on a wide range of structural engineering topics.

Check out the IABSE Website … http://www.iabse.org/publications/orderform/ … and get yourself a copy … pronto !

 

In previous posts concerning Areas of Rescue Assistance in Buildings, for example, I have often referred to robust, fire resisting construction

Robust (in the above specific context):  Structurally hardened, and resistant to severe mechanical damage during the fire and for a period of time afterwards, i.e. the cooling phase.

The further development of Fire-Induced Progressive Damage … will inevitably take place within wider considerations of Robustness.

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