SEO Unique Fire Suppression Design

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UNIQUE FIRE SUPPRESSION DESIGN FOR SINGAPORE AIRLINES HANGAR

Presented by:

Joseph SeoDirector, ABL LIM (FPC) PTE LTD

Singapore Office of Hughes Associates, Inc. USA

Presented at:

The International Forum on Emergency and Risk Management

Singapore Aviation Academy

10-12 January 2005

Abstracts

Aircraft hangars 4 & 5 of the SIA Engineering Company are the newest

maintenance hangars in Singapore. Hangar 5 has been completed in December2004 while hangar 4 is currently in the final stage of installation. Foam-water

system in the hangar floor and closed-head wet type sprinkler at the hangar roof

are installed at both hangars following the NFPA 409 standard. The systemutilized the latest fire protection technology in the protection of aircraft hangar.

Many considerations were built into the system design, installation and testing to

ensure that the fire protection systems would perform satisfactorily since this is

the first aircraft hangar in Singapore ever built with such an advanced fireprotection system. The main objective of the fire protection systems attempts to

address and overcome the limitations at the existing hangars while conforming to

the latest changes in the protection of aircraft hangars.

This paper will present the fire protection design concept & specification adopted

in the new hangars.

SERVICE OF SIAEC

SIA Engineering Company (SIAEC) was formed on 1 April 1992 from the Engineering Division

of SIA and is a subsidiary of Singapore Airlines. SIAEC has a staff strength of over 4000 and an

expanding customer base of more than 80 international air carriers. SIAEC carried out minor and

major maintenance, repair and overhaul (MRO) of aircraft, engines and related components. Asa subsidiary of Singapore Airlines, SIAEC plays a key role in providing engineering excellence

to its parent company ensuring excellent safety record. To maintain this goal, SIAEC employs a

pool of highly skilled and well-trained professionals in the everyday running of the hangaroperations.

Services provided at the maintenance hangars of SIAEC include the following: -

Aircraft Ground Handling

Unique Fire Suppression Design



Aircraft Maintenance and Overhaul (MRO)

Component Repair and Overhaul

Engine & APU Maintenance and Overhaul

Technical Training

Anticipating favorable business in FY2005, the company has embarked to construct 2 new

aircraft hangars to increase its airframe maintenance capacity by 30%. Of the 2 hangars, onewould be constructed with the necessary provision of turning it into a paint hangar.

EXISTING FIRE SYSTEMS

The existing aircraft hangars utilize an automatic foam/water deluge system as its primary fireprotection system in conformance to the NFPA 409: 1995 edition. The deluge system is

activated by the heat detectors while the UV/IR detectors provide prompt detection to alert the

in-house fire fighters monitoring the hangars. Alarm signal is also transmitted to the airport firebrigade in the event of an alarm condition. Foam hose reel stations and wheeled and portable

fire extinguishers are also strategically located at the hangar bay floor to enable prompt fire

containment by the in-house fire fighters. As part of the airport authority’s requirement, the fire

alarm is transmitted through a dedicated DECAM line to the airport fire brigade.

The annex building connected to the hangar bay is fire separated to prevent any fire from either

side to affect the other. Standard response wet-type sprinklers are installed to protect the annex

building that houses the workshop, office and other ancillary rooms. Fire alarm system thatincludes smoke detectors within electrical and AHU rooms and also call point and alarm bells are

installed. To assist fire fighting, a dry riser is installed enabling the fire fighters to connect and

draw water from the external fire hydrant or fire engine. Hose reel are also installed to enable

building occupant to fight any fire that may occur in the annex building.

LIMITATIONS OF EXISTING SYSTEMS

Fire protection system is crucial to the safety of the hangar operation and lives of personnel

working within the hangar bays. It is therefore important that all fire protection systems aremaintained and kept functional according to industrial standards so that any fire can be

effectively contained without undue damage that can disrupt hangar operations. The largehangar space and sheer height however, creates a unique challenge to carry out servicing and

maintenance of the fire devices such as detectors at the ceiling level. In addition, any

maintenance work at the ceiling would render at least a portion of the hangar inoperable orinvolve aircraft relocation which disrupts work flow. From the business view point, such is

definitely not a situation where the management would like to see especially when it involves

extended period of downtime to the revenue generating hangar operations.




Another unique situation for the existing aircraft hangars arise due to the use of low-expansionoverhead foam/water system following the earlier NFPA 409 code prior to the 2001 edition. The

overhead foam/water system when activated is designed to ‘flood’ the entire hangar space

causing foam solution to cover the entire hangar space. The risk of extensive cleaning work, theamount of time required and not mentioning damage to aircraft parts and its electronics, would be

a big problem in the event of a false alarm causing a discharge of the overhead foam/watersystem.

The overhead foam/water deluge system also demands more foam and larger system as theheight of the hangar increases. At the existing hangars, a complex system of circuit logic is in

place to activate the designated zones of the deluge system based on the location of the source of

fire. This arrangement however, is not fool proofed since it is possible for fire to occur anywhereeven in between zones where confusion might arise. In summary, the overhead foam/water

system was expensive to use due to its high demand for foam concentrate and water and also the

high damage potential to aircrafts in the event of a system discharge.

The risk of an accidental discharge of foam/water system is also directly linked to the reliabilityof the UV/IR detectors installed also at the ceiling level. Our office has conducted a number of

laboratory type full scale tests on the UV/IR detectors. The findings of the tests reveal that

UV/IR detectors are susceptible to false alarms and the triple IR detectors can provide improveddetection and false alarm immunity.

THE NEW HANGARS

The latest aircraft hangars in SIAEC consist of 2 steel structure hangars that are large enough to

cater to the latest Airbus A380 passenger aircraft. Hangar 4 has a base footprint of 45 x 76.5meters with a height of 18 meters while Hangar 5 occupies an area of 72 x 100 meters with a

height of 23 meters measured to the underside of the roof truss. Hangar 5 has been constructed

with the provision and intention to convert it into a paint hangar should the need arise.

THE DESIGN SPECIFICATION

General Consideration

In the formulation of the fire protection concepts for the protection of the hangar bay, it was

desirable to address the shortcomings that the existing hangars were facing. A systemconforming to internationally accepted standards with proven technology is also necessary since

the hangars are designed to cater to a wide range of aircrafts from different manufacturers. As

maintenance to any equipment installed at the hangar areas would be difficult to access

especially at the roof, the selected product must be reliable and offers easy means to maintain oreven replace them when necessary.




We have therefore identified and prioritized the following design guides: -

Fire protection system conforming to NFPA 409 standard and local authority’s

requirement while at the same time giving due consideration to insurer’s requirement.

Maximize use of latest technology in fire detection while keeping cost down

Reliability, ease of servicing and maintenance of system.

Minimal or no obstruction to the hangar operations

Based on the requirement stipulated in NFPA 409: 2001 edition, both hangars exceed a fire area

of 3716 m2 (40,000 ft2) and are therefore classified as a Group 1 hangar. NFPA 409 recommends

the following means of fire protection for Group 1, fueled aircraft hangars: -

(1) A foam-water deluge system as the primary fire suppression system. In addition,

supplementary protection systems shall also be provided, or

(2) A combination of automatic sprinkler protection and an automatic low-level

low-expansion foam system, or

(3) A combination of automatic sprinkler protection and an automatic low-level

high-expansion foam system.

We have selected and recommended option 2 above to the client in consideration to the

limitations of the current system in the existing hangars stated above. Looking at the productsavailable on the market, we selected the Grate Nozzle developed by Viking and the U.S.

Department of Defense. Hughes Associates, Inc. USA assisted in the development and testing of

the prototype nozzles which resulted in the development of the Grate Nozzle.

The Grate Nozzle is designed to cover the middle portions of the hangar while fixed-type foammonitors are strategically located to cover the sides. In this arrangement, there is no obstruction

to the aircraft operations especially in the centre of the hangar while providing some degree of

adjustability to the foam system using the foam monitors. Working in tandem with the foamsystem is a triple infrared optical (I3R) flame detection system providing better early flame

detection and greater immunity to false alarm than the UV/IR detection. Water hose reel systems

are installed in the hangar areas to provide a means of fire fighting by the occupants. These handhose reel permits application of water or foam either water spray or straight water streams on

each side and also capable of reaching into the interior of the aircraft.

Fire Separation

In the consideration of the active fire protection system in the hangars, the need for adequate

passive fire separation between the 2 hangars was also specified. Comparing the requirement

under NFPA 409 and the local fire code, the requirement in NFPA 409 was used as the minimum




fire resistance rating since it is more stringent. All elements of structure are therefore 3-hrbetween hangars and 1-hr between hangar and other areas. All main structural steel columns are

made fire resistant using listed fire board to provide a fire resistance rating of not less than 2-hr as

required by NFPA 409. Draft curtains are provided at the roof of each hangar subdividing it intoareas of not more than 697 m2 (7500 ft2) per zone to improve detection and sprinkler response

times.

To reduce fire exposure around the hangars, minimum clear space distances of 7.5 meters (25 ft)

is specified. Additional hangar beside hangar 5 may be constructed in the future and the need tolimit fire exposure will be revisited again.

Each hangar bay area is covered by independently activated overhead closed-head wet type

sprinkler and also low-level Aqueous Film-Forming Foams (AFFF) foam-water systems. All fireprotection systems are connected to a common main fire alarm panel to provide the necessary

system monitoring following the code requirement.

Design Parameters

The approach towards the foam-water system is a fixed-type, low-expansion AFFF utilizing acombination of trench and oscillating monitor nozzles in order to cater to the possibility of a fire

occurring within any part of the hangar. This arrangement offers maximum flexibility in the

usage of space while keeping system & maintenance cost low.

The design application rate is 4.1 L/min/m2

at 3% foam concentrate for a minimum of 10 minutes,achieving distribution of foam solution over the entire hangar to within 1.5m of the perimeter

walls and doors within 3 minutes. Manual actuation stations are provided for each low-levelsystem both at the Fire Control Room on the 4

thfloor and also on the hangar floor adjacent to the

exit nearest to the front of the hangar. To prevent unwanted discharge of foam in the event of a

false alarm, an emergency shut-off button is provided at the Fire Control Room.

The design parameters for the Grate Nozzle are specified by the product manufacturer. For thisproject, the trenches are spaced 15.2 meters (50 ft) apart and the nozzles fitted at an interval of 7.6

meters (25 ft). One of the design issues we had was the need to maintain uniform dischargepressure within the listed operating pressure range of 275.8 to 310.3 kPa to the nozzles as

required by the system manufacturer. It is not an issue with Hangar 4 but the discharge pressure

at the furthest portions of Hangar 5 falls below the permissible pressure range. To resolve this

problem, 1 foam pipe is provided to serve the furthest 3 grate nozzles while a separate foam pipesupplies the rest of the nozzles in each of the 3 trenches for Hangar 5.

The foam monitor nozzles selected is a non-air aspirating, oscillating type with locking pins

provided to define the discharge pattern limits. Every monitor is fitted with a manual shut-off valve. When in service, the manual shut-off is designed to locked-out to provide for automatic

operation only.




The entire foam system is served by a total of 5 diesel driven fire pumps and 4 jockey pumps.Two fire pumps supply the foam portions while the other three fire pumps supplies the water

portion of the foam system. With the exception of the 2 foam pumps which are positive

displacement pumps, all other fire pumps are centrifugal pumps. The fire pumps when activatedwill develop 32 m3 /min (32,086 litre/min) at a pressure of 7.7 bar of water and about 1 m3 /min

(1,007 litre/min) of foam solution.

The overhead quick response wet-type sprinkler fitted with quick response 79oC glass bulb is

designed with a minimum density of 7.5 L/min/m2

over any 1,394 m2

area, covering thehydraulically most unfavorable area of operation. Two diesel driven fire pumps and 2 electric

driven jockey pumps, all pressure actuated, are installed to discharge about 12 m3 /min (12,011

litre/min) at a pressure of 6.53 bar.

A foam hose reel system is installed in the hangar to discharge foam solution from two individual

stations each at a rate of 0.23 m3 /min (227 litre/min) for a period of 20 minutes. To ensure that

the foam hose reel system is able to reach into the aircraft, 1 foam hose reel station complete with

self-contained foam tank is fitted near to the midway into each hangar by the side of the hangarwall. The water hose reel system is supplied by separate hose reel pumps strategically located

within the hangar.

The water supply to all the fire protection systems is provided via a 2-compartment concretewater tank located at the basement having an effective volume of 2775 m3. The required water

storage based on the hydraulic calculations is 2,438 m3 for a period of 45 minutes. The amount of

water supply is sufficient to satisfy the combined usage of the low-level and overhead sprinkler

systems including 2 hose streams. The amount of foam supply required by the foam-watersystem is 10m3 (1007 liters) for a discharge time of 10 minutes. Another 100% reserve supply of

the same foam is also provided and can be introduced manually into the system through a

separate pipe work as required by NFPA 409.

All the trenches are sized to cater to the design flow of both the sprinkler system at the roof and

the low-level foam-water system including the foam hose reel system operating simultaneously.To aid in flow and prevent buildup of flammable liquids in the trenches, all trenches are graded to

prevent accumulation of flammable liquids. Drainage arrangement is designed to allow non-fire

discharge to flow into the effluent treatment plant. In the event of a foam discharge, all discharge

is diverted automatically to flow to the open sea.

Another criterion that we had included in the design specification is the need for this new fire

protection system to cater to additional hangars that SIAEC may build in the future. An increase

in size (both flow and pressure) of the pumps, water & foam storage tank and other arrangementwas specified to meet the expected pressures of future hangars.

Moving onto the fire alarm & detection system, the entire concept of design hinged on the use of

a proven and reliable system that complies with international acceptable standard and industrial

practice. The fire detection system adopted at the hangar areas is an advance optical flamedetection system utilizing triple Infra-Red technology that continually monitors three IR spectral

bands. With the many experiences that our head office has accumulated on aircraft hangar fire

protection working with the US Navy and also in other aircraft hangar projects, we proposed the




use of triple infrared (IR3) optical flame detectors for the protection of the hangar bays. 2detectors (Spectrex or Detronics) from two different manufacturers were indicated in our design

specification as acceptable since both detectors are of similar detection technology and are all

FM/UL approved products. The final choice made by the design & build contractor is the modelX3300 multispectrum IR flame detectors developed by Detector Electronics.

Detectors are situated so that every portion of the protected floor area is within the field of view

of at least two detectors, taking into account fixed obstructions. The detector assembly’s

mounting device is adjustable and capable of retaining the set position. The triple IR flamedetectors are mounted on the walls at 3 & 6 meters above the hangar floor. The lower level

detectors cover the under wing areas of the aircraft while the second level detectors are

positioned to see immediately above the aircraft.

The detection of an alarm condition by the first detector will sound the general fire alarm bells at

the hangar and annex areas and also the main control panel at the Fire Command Centre (FCC)

on the ground floor and Fire Control Room (FCR) on the 4th floor. The system is fully

supervised and faults in components & circuits are immediately indicated in the FCC and theFCR. The detection of a second alarm condition in the same zone will cause the sirens that are

installed at the hangar areas to sound. The sound of the siren is also the alarm indicating

actuation of the foam-water system. To prevent accidental discharge of the foam-water system incase of any false alarm, the foam-water system is activated only after the second detector is set

off. One manual activation switch is provided at the hangar floor to permit immediate activation

of the foam-water system when a fire is detected by any hangar floor staff. Following therequirement of the NFPA 409, the low-level foam-water system will activate upon sprinkler

water flow to the sprinkler system at the ceiling of the hangar. In addition to the general fire

alarm, all alarm signals are also transmitted to the Airport Emergency Service as part of the

airport authority’s requirement.

THE INSTALLATION CHALLENGE

Economic Down Turn in Asia

It is unfortunate that the economic crisis hit Asia between 2002 and 2003 at the time when piling

work was well underway for the new hangars. The management of the client had to temporarily

stop work on site since it was deemed no longer viable to construct the hangars with theeconomic uncertainty looming all over Asia. The SARS outbreak in Singapore also dealt another

blow to the project. The project was thereafter called to a stop at around Oct 2002 as a result of

the economic crisis and the SARS outbreak in Singapore. The project resumed constructionsometime May 2003 at the turn of the economic situation in Asia when the management made the

decision to resume construction of both hangars. The effects of the economic downturn and the

impact of the SARS however, left a great impact in the contract schedule disrupting the smooth

execution of the contract. As a result, additional budget was necessary to restart the installationwork.

Environmental Concerns




In the design of drainage provision for the foam-water system, it was necessary to providecontainment to hold the foam solution unless approval is granted by the local environment

authority – Pollution Control Department of the National Environment Agency (NEA) for direct

discharge to the open sea. In the design consideration, it was deemed economically not viable toconstruct a holding tank that can take the discharged foam solution and sprinkler water in the

worst case scenario. The main concern that the NEA has for this proposal was environmentalcontamination should the foam solution be discharged directly to the open sea. Discussions withthe NEA were conducted to show to them that the level of pollution due to foam solution is

extremely low. This is because the foam solution comprises only 3 percent foam concentrate and

97 percent water and the foam discharge time is a maximum of 10 minutes. The material safety

data sheet for the foam concentrate also revealed that the chemical compounds are within thepermissible limits. Given the reasons above, NEA finally granted our proposal to divert the foam

solution directly to the open sea instead of building a giant holding tank in the event of a genuine

emergency condition. It is however required that vacuum trucks be employed in all other casessuch as testing and training.

Availability Of Equipment And MaterialsThe project restarted after much communication between the owner, project team and the

contractor. At this time, however, the construction industry in Singapore was so very badlyaffected that many smaller companies could not weather it through. Some equipment and

materials had to be sourced from alternative supplier resulting in higher cost. The cost escalation,

at least for the fire protection was nevertheless under control since most of the high cost hardwaresuch as pumps and controllers were secured and shipped to site before the project was

temporarily stopped. There were nevertheless some equipment and materials that were cancelled

had to be re-ordered resulting in delay in delivery impacting the project schedule.

Multiple Trades Working Simultaneously

After resolving many of the equipment and materials issues, another situation again disrupted the

flow of the project. Due to the anticipated increase in hangar operations, the owner instructed anescalated pace in the construction. This would not be a problem in the original project schedule

but affected the sequence of site work. Different trades had to work concurrently in order to meet

the project schedule. A lot of planning and site coordination were needed to resolve conflicts ininstallation sequence, minimize abortive works and ensure that project schedule is maintained as

far as is practically possible. One lesson learned on this aspect is the importance of effective site

coordination amongst all parties especially in fast-pace project such as this one.

With determination and commitment of the team of consultants and the main contractor, the first

hangar was completed and obtained its Temporary Fire Permit by 15 December 2004 achievingthe target date as required by the client. As I am speaking here, work is ongoing at the site and on

schedule to complete the second hangar by March 2005.

TESTING & COMMISSIONING

The system testing and commissioning requirement specified in our design specification




mandates complete performance and functional test of all components and equipment used in thefire protection systems. Although both hangars are supplied from the same pump sets and

storage tanks, separate sprinkler and foam-water system test is specified. One of the main

reasons for a repeated test, especially for the foam-water system, is the concern that actual fieldtest for the foam equipment would not come easy with the expected volumes of hangar

operations.

We had conducted the first foam-water system field test successfully on 10 December 2004. On

that day, a total of 6 tests were conducted on the foam-water system. They were: -

Test 1: Hose Reel (Water)

Test 2: Hose Reel (Foam)

Test 3: Foam Monitor (Water only)

Test 4: Foam Monitor (Foam)

Test 5: Grate Nozzle (Water only)

Test 6: Full Foam Discharge Test (Grate Nozzles and Foam Monitors)

Test 7: Full System Discharge (Clean-up)

Results from the tests conducted shows that the foam-water system performed as expected

according to the performance criteria stipulated in NFPA 409.

LOOKING FORWARD

It has been a challenge from system designing to installation to system completion and finally

witnessing the successful putting into operation of the first new hangar. Throughout the entire

period of construction until completion, many issues arise requiring the professionalism andcommitment of the team and contractor to resolve them without jeopardizing the schedule and

progress. With the experience gathered for the first hangar, the installation work at the second

hangar is expected to be much better.

With the new approach towards fire protection adopted in Hangar 4 & 5, many limitations thatcurrently restrict maintenance work in the existing hangars would not happen. In addition, thelatest fire protection technology and equipment used are better equipped to screen out false

alarms thereby improving system accuracy and reliability. It is hope that through regular upkeep

of the hardware and software, the fire protection system would be able to pay-back itself with a

good record of keeping the hangar safe from fire.




REFERENCES

1. NFPA 409, Standard on Aircraft Hangars, 2001 Edition published by National Fire

Protection Association USA

2. NFPA 11, Standard for Low-, Medium-, and High-Expansion Foam, 2002 Editionpublished by National Fire Protection Association USA

3. NFPA 13 Standard for the Installation of Sprinkler Systems, 2002 Edition published by

National Fire Protection Association USA

4. Optical Fire Detection Technologies for Technologies for Aircraft Hangars by Dr. Daniel

T. Gottuk Hughes Associates, Inc. & Mr. Joseph E. Gott, NAVFAC, & Dr. Frederick W.Williams, NRL, & Dr. Gary Lougheed and Mr. George . Crampton, NRC

5. NFPA 409: 2001 Standard on Aircraft Hangars, A comparison of Foam Systems by

Alison Wakelin, Hughes Associates, Inc.


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