telecommunications and data processing facilities …

TELECOMMUNICATIONS AND DATA PROCESSING FACILITIES DESIGN GUIDE

June 2020 Doc. No. 11782_15

Telecommunications and Data Processing Facilities Design Guide VESDA

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Disclaimer The contents of this document is provided on an "as is" basis. No representation or warranty (either express or implied) is made as to the completeness, accuracy or reliability of the contents of this document. The manufacturer reserves the right to change designs or specifications without obligation and without further notice. Except as otherwise provided, all warranties, express or implied, including without limitation any implied warranties of merchantability and fitness for a particular purpose are expressly excluded.

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General Warning This product must only be installed, configured and used strictly in accordance with the General Terms and Conditions, User Manual and product documents available from Xtralis. All proper health and safety precautions must be taken during the installation, commissioning and maintenance of the product. The system should not be connected to a power source until all the components have been installed. Proper safety precautions must be taken during tests and maintenance of the products when these are still connected to the power source. Failure to do so or tampering with the electronics inside the products can result in an electric shock causing injury or death and may cause equipment damage. Xtralis is not responsible and cannot be held accountable for any liability that may arise due to improper use of the equipment and/or failure to take proper precautions. Only persons trained through an Xtralis accredited training course can install, test and maintain the system.

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Preface This Design Guide provides guidelines in the design and deployment of VESDA smoke detection systems in telecommunications, data processing and information technology facilities. The environments envisaged include the following:

• Fixed and wireless telecommunications facilities. • Small remote site equipment enclosures, such as those used to house wireless transmission equipment. • Data processing and computer facilities including server rooms, internet data centres, data warehousing

facilities and co-location centres, containerized or mobile “data centres”. • Telecommunications/data communications and underground cable tunnels/vaults or controlled

environmental vaults (CEV). • Terrestrial and satellite broadcast facilities for radio, television and the Internet. • Power and other essential services support infrastructure for the above installations.

In the remainder of this Design Guide, the above environments will be referred to as “IT/Communication Facilities”.

Note! The information contained in this Design Guide should be used in conjunction with specific local fire codes and standards as well as the guidelines provided in the VESDA System Design Manual. Where applicable, other regional industry practices and end user practices should also be adhered to.


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Contents 1 Background ............................................................................................................................................ 1

Fire Safety Considerations in IT/Communication Facilities ................................................... 1 Performance-Based Design ....................................................................................................... 1 Key Design Considerations ....................................................................................................... 1 Why Use VESDA Smoke Detection? ......................................................................................... 2

2 Design for Effective Protection ............................................................................................................ 3 Protection Levels ........................................................................................................................ 3 Return Air Protection .................................................................................................................. 4 Ceiling Protection ....................................................................................................................... 5 Raised Floor and Ceiling Void Protection ................................................................................ 7 Inter-Beam Sampling .................................................................................................................. 8 Combined Coverage Technique for Small Spaces .................................................................. 8 Localized Protection – Cabinets ................................................................................................ 9 High-Risk Equipment Protection ............................................................................................. 10 Cable Tunnel/Vault Protection ................................................................................................. 11

Cable Trays ................................................................................................................................ 11 Containment Aisles ................................................................................................................... 11 Outside-Air Monitoring (Reference Detection) ....................................................................... 17

3 Integrating Smoke Detection and Fire Suppression ........................................................................ 19 Alternating VESDA Sampling Pipe Option ............................................................................. 20 Single VESDA Detector Options .............................................................................................. 20 VESDA Ceiling (Raised Floor)/AHU Option ............................................................................ 20 Hybrid Detection Technologies Option .................................................................................. 21

4 Commissioning, Service and Maintenance ...................................................................................... 22

5 VESDA Cause and Effect Sequence .................................................................................................. 23

Disclaimer On The Provision Of General System Design Recommendations ........................................ 24


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1 Background Fire Safety Considerations in IT/Communication Facilities

Major fire risks within IT/Communication Facilities include the following:

• Overheating of electrical cabling, electrical relays, and signal processing equipment. • Equipment electrical faults i.e. arcing of transformers, and power supplies. • Equipment malfunctioning i.e. generators, and Air Handling Units (AHU). • Improper house-keeping practices, such as storage of materials near hot surfaces. • Densely packed arrangement of equipment will encourage the spread of fire. • The ventilation ductwork might circulate smoke and gases to other compartments. • Risk of explosion from flammable gases in battery rooms, CEV, and cable tunnels/vaults.

Note! Air Handling Unit (AHU) includes Heating, Ventilation and Air Conditioning Systems (HVAC), computer-room air conditioners (CRAC), computer-room air handlers (CRAH).

Performance-Based Design The design of most VESDA systems in IT/Communication Facilities are prescriptive in nature, however, alternative Performance Based Designs (PBD) might be used to supplement these practices in cases where the facility configuration is not addressed in codes, or where an improved design with greater sensitivity, coverage and/or flexibility is deemed necessary in areas housing critical equipment.

Examples of prescriptive and PBD approaches and risk management concepts are listed below:

• NFPA 75 Standard for the Protection of Electronic, Computer/Data Processing Equipment. • NFPA 76 Recommended Practice for the Fire Protection of Telecommunications Facilities. • FM Global 5-32 Data Centers and Related Facilities Property Loss Prevention Datasheet. • BS 6266 Code of practice for fire protection for electronic equipment installation. • ISO 31000:2009 Risk Management – Principles and Guidelines. • SFPE Handbook of Fire Protection Engineering.

Performance based fire protection solutions can be made to comply with the performance objectives of local and national codes and standards for buildings and life safety. Assessments of the environmental risks and performance requirements, specific to the particular IT/Communication Facility, are conducted as part of the design process.

Key Design Considerations Designing an effective solution takes into consideration coverage objectives, requirements, and the environment. Multiple coverage techniques are possible and generally a space will use more than one method for an effective level of protection. Careful consideration must be given to selection of detector, pipe and fittings and ancillary items needed to form an effective system capable of meeting all performance objectives and efficiency requirements. A holistic view of the facility should be evaluated, taking into consideration inter-dependent adjacencies that could affect reliability and uptime objectives should an event occur.

The following should be considered when specifying and designing a VESDA smoke detection system in an IT/Communication Facility:

1. What do prescriptive codes / standards and industry practices require or recommend? 2. What do Performance Based Design codes require or recommend (NFPA75, NFPA76, BS6266)? 3. Are there insurer requirements? 4. Are there owner defined practices? 5. What level of protection is required and how will fire safety be managed?


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6. What are the risks? Criticality of data, financial loss as result of down time? 7. Which method(s) of protection are required (ceiling, raised floor, ceiling void, return air vent, cabinet,

cable tunnels/vaults, outside air intake, etc.)? 8. What are the structural features (ceiling configuration, horizontal obstructions, vertical elevations, etc.)? 9. What are the environmental characteristics (temperature, ventilation schemes, pressure differentials,

humidity, air exchange rate, airflow direction, etc.)? 10. Is there a need or desire to localize detection within or in close proximity of equipment? 11. Is there a need to create zones for source location purposes and/or releasing systems? 12. Is there a need to integrate suppression with a desirable coincidence / cross-zoning detection scheme? 13. What do gaseous suppression codes recommend (AS4214.1, NFPA2001, BS7273-1)? 14. Site accessibility (time to get to a remote unmanned site) 15. Accessibility for maintenance, test and inspection within raised floor, ceiling void, above cable trays,

within fully or partially enclosed equipment cabinets, restricted areas, etc.

Why Use VESDA Smoke Detection? Fire events in IT/Communication Facilities must be detected as early as possible to ensure personnel safety, asset protection and the avoidance of business interruption. VESDA mitigates risk of fire and consequences of downtime in IT/Communication Facilities in the following ways:

• VESDA detectors detect fires at their incipient stage, allowing early intervention for investigation and action; before smoke and corrosive gases affect equipment and personnel.

• Early intervention reduces the reliance on suppressant release or fire brigade call-out. • VESDA detectors monitor all fire stages from incipient to fully developed, providing multiple alarms for

staged response. • A VESDA system can be designed to reliably detect diluted smoke due to its very sensitive sensing

chamber and cumulative sampling (smoke drawn through multiple sampling holes). • The VESDA system can be designed to accommodate temperature and humidity extremes. • The VESDA system can monitor HVAC outside air intakes and adjust smoke readings to avoid nuisance

alarms from outside sources. • When designed and appropriately commissioned, there is a comparatively low incidence of false alarms

with a VESDA system due to filtration, dust discrimination, programmable alarm thresholds and alarm verification delays.

• Where a gaseous or sprinkler fire suppression system forms part of the overall fire protection solution, the VESDA system can be designed to actuate the release mechanisms flexibly with various systems, from non-interlocked to double-interlocked systems, by different detection schemes including coincidence detection.

• VESDA detectors can be mounted in easily accessible areas. This allows for easy and safe system maintenance when sampling in awkward locations such as raised floors, ceiling voids and underground cable tunnels/vaults, will not disrupt operations and will not cause security breach of secure spaces.


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2 Design for Effective Protection Protection Levels

The VESDA system can be designed to provide two levels of protection based on coverage area, sampling hole distribution and sensitivity:

1. Good Practice – The system is designed to meet local prescriptive codes and standards plus PBD solutions for loss prevention and business continuity.

2. Best Practice – The system is designed to meet the above and provide maximum protection possible and form an integral part of the overall risk management strategy.

Table 1: Recommended guidelines for IT/Communication Facility protection Application Good Practice Best Practice

Return Air

Ceiling Protection

Raised Floor where combustibles are present

Ceiling Void where combustibles are present

Fully or partially enclosed Server Cabinets

High Risk Equipment and Power Distribution Panels

Cable Vaults or Tunnels

Air Containment Structures

Outside Air Monitoring (Reference Detection)

In this Design Guide, the recommended guidelines for protected areas are based either on local fire codes and standards, Performance Based Design guidelines or Xtralis application testing. Target hole sensitivities are determined based on levels of risk, environmental and operational characteristics of the area being protected. or may be dictated by local codes, standards or end user practices.

Note! All pipe network designs must be verified by the Xtralis Pipe Network Modelling Tool, ASPIRETM.


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Return Air Protection In IT/Communication Facilities, the majority of smoke will follow airflow distribution paths of the circulated air and might not reach ceiling detection points. This can be overcome by complementing ceiling with sampling across where air leaves or returns within the space, such as at return air grilles on self contained CRAC units serving the space, transfer grilles or openings between spaces, etc. (Figure 1).

Figure 1: Example of VESDA pipe arrangement on a grille for return air protection.

The maximum sampling hole coverage area must adhere to codes and standards. NFPA 76 and BS6266 as an example recommend a maximum area of coverage per sampling hole of 0.4 m2 (4 ft2).

To avoid adverse pressures the VESDA pipes should be positioned 100 to 200 mm (4 to 8") away (using stand- offs) from the face of the grilles or openings with sampling holes oriented at an angle of 20-45° downward to the incoming air. These recommendations also assist in eliminating flow faults from changing airflow conditions caused by a change in the operation of the AHU.

Figure 2: Sampling hole at 30° angle to incoming air. Horizontal flow with hole facing downwards

One single VESDA detector can monitor more than one return air path provided maximum transport times is less than 60 seconds and target sampling hole sensitivity is maintained. Where individual fan shutdown is required, the VESDA detector must be dedicated to the AHUs corresponding return air path.

In summary, the following should be considered for return air protection:

• The use of sampling pipe stand-offs from the face of the return air grille or opening is critical, especially when multiple grilles or openings are being monitored by the same detector.

• For very early warning smoke detection, air sampling should be conducted upstream from the AHU to avoid smoke removal from fan and filters. Where protection against malfunction of the AHU (fan, belts) is required, sampling should be conducted at the AHU supply air vent.

• Use of socket unions helps ensure the correct pipe orientation with respect to the airflow direction (20-45°) and removal of pipe where access behind a grille may be necessary.

• Good pipe network design practices such as minimizing the total pipe length and number of bends should also be considered. Sealed end caps outside the grille or opening area are required.

Note! It is essential to test the system performance, with the AHUs in their normal operating mode and turned off, to check that sampling pipe position and orientation are correct.

Return Air Grille

Sampling Hole Sealed

End Cap


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Ceiling Protection For an air sampling-type smoke detector, sensitivity at the detector is not equal to sensitivity at the sampling hole. Sampling hole sensitivity is dependent on two main factors:

1. The number of sampling holes in the piping network 2. The set alarm sensitivity of the detector

For the detection of smoke in open areas in accordance with codes and standards and end user practices:

1. Provide appropriately sized and number of VESDA detectors to efficiently and adequately cover designated area(s).

2. For suppression cross zoning and source location purposes, when required, utilize VESDA VES addressable VESDA Aspirating Smoke Detector.

3. Air sampling pipe distribution networks are constructed using rigid pipe mounted to the underside of the structural ceiling as shown in Figure 3. Sampling holes are drilled directly into the air sampling pipe distribution network and oriented downward.

Figure 3: Example of air sampling below structural ceiling

4. For ceilings that have beam, girders, solid joist or waffle-like construction and are defined by local codes and standards as a beam pocket, refer to section 2.5 (Inter-Beam Sampling).

5. Where drop ceilings are present, sampling holes can be remotely mounted to the underside of the drop ceiling via flexible “capillary” tubing (Figure 4).

Figure 4: Example of capillary air sampling through false ceiling

6. The recommended maximum coverage per sampling hole in these conditions is typically 50% of standard detection which is 18.6m2 (such as NFPA76) and 25m2 (such as AS1670.1 and BS6266), exception being where obstructions such as HVAC ductwork would otherwise prevent this spacing objective from being met, in which case placement should be just outside perimeter of obstruction. A typical sampling hole arrangement is specified by a grid as shown in Figure 5.


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Figure 5: Example of grid arrangement of ceiling VESDA sampling holes

7. Sampling holes should be installed in an area of the ceiling that is free from obstructions for a minimum of at least 457mm (18 inches) on all sides.

8. Placement of sampling holes nearest to walls should be greater than 304mm (12 inches) and not exceed half the listed spacing, measured at right angles.

9. Congestion at the ceiling such as HVAC ductwork, fully loaded cable trays and other physical obstructions has the potential of significantly delaying or entirely obstruct smoke from reaching sampling holes placed directly below the ceiling. High/low sampling configurations are intended to overcome physical obstructions by placing layers of sampling holes both at the ceiling and below obstructions. High/low sampling configuration are constructed using either rigid sampling pipe or flexible capillary tubing teed off the main air sampling pipe distribution network at the ceiling with pipe or tubing extensions below obstructions. Sampling holes are placed within the main air sampling pipe distribution network at the ceiling level and at the ends of pipe or tubing extensions. The maximum coverage per sampling hole for each level is no greater than 18.6 m2 (200 ft2) between high/low points. Refer to Figure 6.

Figure 6: Example High/Low sampling configuration

Note! Where local codes and standards and end user practices dictate placement and spacing of sampling holes that is more stringent than those recommended herein, local codes and standards and end user practices shall prevail.


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Raised Floor and Ceiling Void Protection Raised floors and sometimes ceiling voids of IT/Communication Facilities when present, may contain large quantities of electrical cabling or other combustibles. It is important these areas are protected since the presence of high airflows will lead to rapid spread of fire and smoke. VESDA detectors are well suited to this task with detectors able to be positioned outside the protected area for convenient access for service and maintenance.

Figure 7: Example of Raised Floor protection

The following should be adhered to when protecting raised floor and ceiling voids:

• The VESDA exhaust may need to be returned to the protected area to minimize the effects of pressure differences that may be present between the protected area and the area where the detector is located. Where the void is used as an air plenum, orienting the holes 20-45˚ downward to the incoming flow will further assist to counteract pressure effects and prevent buildup of dust.

• Sampling pipes should be supported using stand-off mounting hardware to provide clearance from cabling at the top of the raised floor or ceiling void.

• Where space is defined as a plenum use only plenum rated material. • For raised floor or ceiling void spaces with high air velocities i.e. >10 m/sec (2,000 fpm)), ideally,

sampling holes should be placed between 1/2 to 2/3 height. In spaces larger than 1000 m2 (10,000 ft2), the sampling holes can be placed in a staggered arrangement (Figure 8) to maximize smoke entry points.

Note! Orient sampling holes 20-45˚ downward to the incoming flow. Refer to Figure 8 for sampling holes orientation details.

Figure 8: Example of sampling holes zigzag arrangement in high airflow raised floor/ceiling void (bottom view)


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Inter-Beam Sampling Depending on the size of the voids and the depth of the beams, it may be necessary to sample within each inter-beam space or pocket or underside the beam in order to comply with local codes and standards. This type of sampling can be achieved using walking stick shaped pipe extensions from the main pipe into the inter-beam spaces (Figure 9) using either rigid pipe or capillary tubing.

Figure 9: Example of walking stick pipe extensions for inter-beam and underside ceiling beam sampling

Combined Coverage Technique for Small Spaces In small IT/Communication facilities or small areas within a larger facility housing IT and communication equipment it is possible to use a single VESDA detector to cover up to three different sections of the room; ceiling, below raised floor or within ceiling void, plus return air grille. Figure 9 shows ceiling and return air grille protection using the same VESDA detector. For single pipe inlet detectors, a branch shall be used for each protection level. For multi-pipe inlet detectors, individual pipe inlets should be used for each protection level, or branches where a single pipe is used between levels. Consideration should be given to ensure ambient background levels are equal between levels, and that the detectors exhaust is in an equal or lesser pressure not to exceed 100 Pascal’s in relationship to where sampling points are located.

Figure 10: Example of combined coverage detection (ceiling/AHU return) using a single detector


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Localized Protection – Cabinets Partially enclosed cabinets containing electrical equipment are usually ventilated vertically (bottom to top) or horizontally (front to back) or could be fully enclosed with active internal cooling. There are two methods for protecting cabinets with VESDA detectors; microbore and large bore systems:

1. Microbore system:

VESDA-E VEA detector is ideally suited for localized cabinet detection where a fire event can be readily identified and traced to an individual cabinet (Figure 11). Sampling locations should be directly in the airflow distribution path where the air exhausts for passively cooled or low-speed active bottom to top cooling cabinet configurations, or at a point where air recirculates within fully sealed cabinets with internal cooling. For microbore systems, the pressure differential between any two cabinets should not exceed 30 Pascals. Where Very Early Warning sensitivity objectives are required, consider use of large bore VESDA systems.

Figure 11: Example of VESDA-E VEA system with microbore tubes for cabinet protection

2. Large bore systems:

For ventilated or fully sealed cabinets with internal cooling, a VESDA large bore detector may be dedicated to an individual cabinet or row or bank of cabinets. For ventilated cabinets, sampling locations should be directly within the airflow distribution path at a point where the airflow exhausts. For fully enclosed cabinets, sampling locations should be at the top of the cabinet, or at a point where air recirculates for sealed cabinets with internal cooling.

A capillary tube (A) or down pipe (B) with vented end cap is inserted in the top of the cabinet as shown in Figure 12. A VESDA detector can be used to protect a single row of cabinets (i.e. VEU, VEP, VLF) or multiple rows or banks of cabinets (VES). This arrangement is suitable only for sealed cabinets or cabinets with minimal ventilation.

For vertically ventilated cabinets (bottom to top) the sampling pipe is placed close to exhaust vent(s) of the cabinets as shown in Figure 13 with sampling holes directly in the path of the main airflow to optimize the detection. This arrangement allows a fire event to be traced to a particular row or bank of cabinets.

For horizontally ventilated cabinets (front-to back) the sampling pipe is placed close to exhaust side of the cabinets (Figure 14) with sampling holes directly in the path of the exhaust air to optimize the detection. This arrangement allows a fire event to be traced to a particular row or bank of cabinets. For this configuration, the sampling holes coverage area should not exceed 0.2 m2 (2 ft2).

Figure 12: Example of a capillary tube (A) and down pipe (B) used for in cabinet sampling


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Note! For in-cabinet protection, unless otherwise specified, it is recommended that capillary tubes penetrate the cabinet to a depth of 25 to 50 mm (1 to 2”).

Figure 13: Example of protection for vertically ventilated cabinets

Figure 14: Example of protection for horizontally ventilated cabinets

High-Risk Equipment Protection Certain equipment in IT/Communication Facilities are designated high-risk. The consequences of a fire event within such equipment could be disastrous. Examples of these types of equipment include the following:

• Those that are likely to promote a fast developing fire (e.g. high voltage power systems). • Those that will generate corrosive and toxic gas species (e.g. battery systems). • Those whose unnecessary shutdown would result in substantial network service losses (e.g. network

transmission hubs and their power supply systems).

Sampling location considerations are often similar to those for cabinet protection and include the following:

• Sampling should be conducted within or around high-risk equipment for the earliest possible detection of smoke.

• Where appropriate and within the system design capacity, capillary tubes branched from the main sampling pipe may be used to penetrate equipment or equipment cabinets. Normally should be dedicated systems unless in very small rooms.

• All sampling pipes should be airtight, firmly secured and held clear of equipment, especially moving parts to avoid physical damage to the pipe network and/or the equipment.

The VESDA ECO gas detector is recommended for the protection of battery arrays within Uninterrupted Power Supply (UPS) rooms to detect and alert for excessive levels of explosive gases (hydrogen). Ceiling and/or return air vent detection is required for these environments.

Note! VESDA detectors MUST NOT be installed in areas where high EMI/EMC sources are present. A good practice is to install detectors outside the protected area with sampling pipes entering the area where high EMI/EMC sources are present.


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Cable Tunnel/Vault Protection IT/Communication Facilities can house considerable lengths of underground cabling in narrow tunnels/vaults. Cable tunnels/vaults can be protected by arranging VESDA branched sampling pipe networks at the center of the ceiling tunnel or close to the cable trays (Figure 15).

Figure 15: Example of a VESDA detector protecting a cable tunnel

The VESDA ECO gas detector is recommended for cable tunnels/vaults (or CEV) for methane detection and/or oxygen depletion.

Cable Trays The VESDA system can be designed to protect cable trays by placing the ceiling pipe above the trays. Where cable trays might block the movement of air, the VESDA pipe network should be branched using either rigid pipe or capillaries in high level (above the cable tray) and low-level (below the cable tray) configuration. Under such configuration, the high level and low-level sampling holes maximum coverage area should be 37.2 m2 (400 ft2).

Containment Aisles Hot Aisle / Cold Aisle (HACA) In a HACA configuration, equipment is loaded into racks such that all the air intakes, or inlets, face the same way (the front of the rack), and air exhaust, or outlets, consequently, are facing the back of the racks. Furthermore, the racks are oriented in rows such that the fronts of the racks are in line with each other, and the backs are in line with each other. Additional rows are added such that the back of the racks in adjacent rows face each other, creating a hot aisle, and the front of the racks in adjacent rows face each other. Cold air is forced into the aisles in which the rack fronts face each other, creating a cold aisle.

For reliable very early fire detection in HACA configurations the following guidelines are recommended for the VESDA system (Figure 16):

1. Area Detection: • Sampling holes placed at ceiling and below obstructions (High/Low sampling) in accordance with

section 2.3 herein when required by codes and standards or end user practices. • Sampling holes within beam pockets in accordance with section 2.5 herein where combustibles are

present or when required by codes and standards or end user practices. • Sampling holes within ceiling or floor voids in accordance with section 2.4 herein when

combustibles are present or when required by codes and standards or end user practices. 2. At points along air distribution paths prior to air leaving the space or containment structure:

• Sampling holes at AHU return paths serving the space in accordance with section 2.2 herein. • Sampling holes within air ducts in accordance with the Duct Application Note (Doc 35424). • Sampling holes placed within exhaust path of economizers prior to the introduction of outside air.


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• Placed under the shroud within the contained aisle. This is a requirement of some codes (all areas to be individually protected) and also serves to provide protection in the event of a total AHU shutdown, even though an airflow fault will be present.

3. Where protection against malfunction of the AHU (fan, belts, bearings, etc.) is required or desired sampling should occur at the AHU supply air grille.

Figure 16: Hot Aisle Cold Aisle (HACA)

Note! The selection of detection locations, spacing and coverage will depend on the fire risk, cost of business downtime, environmental and operational conditions of the premise. Performance testing (i.e. smoke tests) and/or a performance based design (PBD) approach is recommended to ensure specific objectives are met.

Hot Aisle Containment (HAC) HAC is used to prevent hot air from the hot aisle from escaping and recirculating to the server inlets. This is accomplished by adding solid obstructions to close off the hot aisle.

For reliable very early fire detection in HAC configurations the following guidelines are recommended for the VESDA system (Figure 17):

1. Area Detection outside of hot air containment aisles or structures. • Sampling holes placed at ceiling and below obstructions (High/Low sampling) in accordance with



combustibles are present or when required by codes and standards or end user practices. 2. At points along air distribution paths prior to air leaving the space or containment structure.

• Sampling holes at AHU return grilles and transfer grilles serving the space in accordance with section 2.2 herein.

• Sampling holes within air ducts in accordance with the Duct Application Note (Doc 35424). • Sampling holes placed within exhaust path of economizers prior to the introduction of outside air.

3. Sampling holes within hot air containment aisles or structures at a point just prior to where air leaves the structure. • For collar configurations (Figure 18a) sampling holes are placed along or parallel to the center line

of collar and spaced 1.8m (6ft) maximum linear distance in both parallel and perpendicular directions between holes. Sampling holes shall be oriented 20-45˚ downwards towards the incoming flow. For source location purposes it is recommended each hot containment aisle be served by an individual VESDA zone (e.g. four pipes on VES with each pipe serving an individual aisle). Pressure differentials between pipes and detector exhaust shall not exceed 100 Pascals.

• For chimney configurations (Figure 18b) sampling holes are placed above each chimney at a point prior to where air leaves the chimney and enters the return plenum. Sample holes should be


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oriented 20-45˚ towards the incoming flow with coverage not exceeding 0.2m2 (2 ft2) of chimney area.


Figure 17: Hot Aisle Containment (HAC)

a) Collar Example b) Chimney Example

Figure 18: Hot Air Containment Aisle Ventilation Arrangements


Cold Aisle Containment (CAC) In CAC, the cold aisle is covered on the top and the end of the rows. Cold air is supplied into the contained cold aisle and hot air is exhausted from the cabinets into the room.

For reliable early fire detection in cold containment aisle configurations the following guidelines are recommended for the VESDA system (Figure 19, Figure 20):

1. Area Detection outside of cold air containment aisles or structures: • Sampling holes placed at ceiling and below obstructions (High/Low sampling) in accordance with



combustibles are present or when required by codes and standards or end user practices.


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2. At points along air distribution paths prior to air leaving the space: • Sampling holes at AHU return grilles and transfer grilles serving the space in accordance with

section 2.2 herein. • Sampling holes within air ducts in accordance with the Duct Application Note (Doc. 35424). • Sampling holes within exhaust path of economizers prior to the introduction of outside air.


Figure 19: Cold Containment Aisle (with Ceiling Void)

Figure 20: Cold Containment Aisle (without Ceiling Void)


In-Row Cooling (IRC) With this configuration hot exhaust air from server racks is cooled by in-row coolers positioned between server racks.

For reliable early detection for in-row cooling configurations the following guidelines are recommended for the VESDA system:

1. Area Detection (Figure 21). • Sampling holes placed at ceiling and below obstructions (High/Low sampling) in accordance with


present or when required by codes and standards or end user practices.


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• Sampling holes within ceiling or floor voids in accordance with section 2.4 herein when combustibles are present or when required by codes and standards or end user practices.

2. At points along air distribution paths prior to air leaving the space or cooling structure (Figure 21 - Figure 23). • Sampling holes at AHU return grilles and transfer grilles serving the space in accordance with

section 2.2 herein. • Sampling holes within air ducts in accordance with the Duct Application Note (Doc. 35424). • Sampling holes placed within exhaust path of economizers prior to the introduction of outside air. • For in-row cooling units placement of sampling holes at return air side of in-row coolers in

accordance with section 2.2 herein and as illustrated in Figure 21 - Figure 23. For source location purposes it is recommended each equipment row be served by an individual VESDA zone (e.g. four pipes on a VES with each pipe serving an individual aisle).


Figure 21: IRC Coverage Configuration

Figure 22: IRC Return Air Sampling Hole Placement


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Figure 23: IRC Return Air Sampling Pipe Configuration



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Outside-Air Monitoring (Reference Detection) Certain IT/Communication facilities utilize outside air for economy cooling or to replenish air lost through building leakage. The introduction of outside air has the potential of introducing airborne particulates in the protected area which can increase the ambient background levels in the protected area or lead to equipment contamination.

VESDA detectors can be used for monitoring the outside air intakes of packaged HVAC units or the building’s ventilation system for either referencing purpose and/or providing the signal to terminate the supply of outside air when excessive pollutants are detected.

Referencing of outside air is a common practice in IT/Communication facilities. A VESDA (Reference) detector samples the outside air to determine the level of intake pollutants and subtracts this reading from all other detectors inside the protected area so only a net increase in smoke level within this area will set off an alarm. More details of Referencing configurations, particularly setting up Referencing with VSC, can be found in the VESDA Referencing Application Note (Doc 32486).

The pipe network design considerations when employing packaged HVAC units or building’s ventilation system are:

Packaged HVAC Units Packaged HVAC units can be either roof or ground mounted. They comprise different compartments each one serving a specific function in the conditioning (treatment) of the outside air such as filtration, cooling, humidification, etc.

VESDA sampling pipes are installed horizontally across the make up air intake grille with sampling holes at a 20-45º downward orientation facing opposite the incoming air. The pipe network comprises a water trap close to the detector to capture condensate in the pipe.

The VESDA detector is mounted in the inverted position within a temperature stable compartment of the packaged HVAC unit (i.e. solid state controls compartment) so it is not affected by the external environment (Figure 24) The exhaust pipe should be routed back to the compartment where sampling occurs to minimize the effects of pressure difference.

Figure 24: VESDA arrangement for outside air monitoring - Packaged HVAC units


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Building HVAC Systems For building’s ventilation systems, the VESDA sampling occurs in the ductwork, downstream from the outside air intake damper (Figure 25). A water trap is placed close to the detector to capture condensate in the pipe. Refer to the Duct Application Note (Doc 10760) for further details on pipe network setup.

Figure 25: VESDA arrangement for outside air monitoring – Building Ventilation


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3 Integrating Smoke Detection and Fire Suppression In many IT/Communication Facilities, a fire suppression system is included to protect electronic equipment from smoke and fire damage. Despite their benefits every care should be taken to avoid false suppressant discharges for the following reasons:

1. Business down time 2. Suppressant agents are expensive to replace and ensuing clean up activities will interfere with the

normal operation of the IT/Communication Facility leading to further financial losses. 3. The cooling effect of gas discharge can result in condensation on the exposed surfaces of electronic

equipment, promoting corrosion. 4. The decomposition products of certain suppressant gases are toxic. 5. The decomposition products of certain suppressant gases might contaminate or cause direct corrosion

damage to electronic equipment.

One method to minimize the possibility of false discharges involves using a coincidence (also known as cross zoning) detection scheme. According to the CEA, the “coincidence connection” configuration requires that at least two independent fire detector alarm outputs be signalled to the detection control and indicating equipment before suppression discharge is initiated.

VESDA detectors’ wide sensitivity range, multiple alarm levels and flexible pipe layout designs can provide the signal at the appropriate time for suppression actuation through coincidence detection arrangement.

There are several methodologies that designers employ for the implementation of coincidence detection:

The appropriate VESDA Fire alarm (Fire 2 recommended) for suppression actuation corresponding to coincidence detection equivalency to point (spot) type smoke detectors installed in the same area is determined with the tool used by the installer/consultant.

Xtralis developed a tool, the ASD Suppression Actuation Threshold (ASAT) Calculator, (refer to the ASAT Calculator Product Guide document no. 12748) to calculate the actuation threshold under certain ventilation schemes. Alternatively, designers can set up the suppression actuation threshold as per local code requirements.

Note! Though false alarms are rarely issued by correctly installed and maintained VESDA systems, certain activities (i.e. maintenance) near the sampling pipes could result in a false alarm. It is recommended that VESDA detectors are set to “Stand-by” mode during activities within the protected area and run independently of the suppression system for a period of time, following such activities, to clear any debris from the sampling pipes.

Note! With VESDA very early detection, the potential need for an actual suppression release would be greatly reduced.

Note! The decision to employ any of the suppression actuation options suggested in this document must be made by an experienced fire system designer, be founded on a sound risk management-based engineering assessment and be complaint to local codes and standards.


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Alternating VESDA Sampling Pipe Option Coincidence detection is provided by two separate VESDA detectors either on the ceiling or within raised floor with interlaced pipe networks while maintaining the required sampling hole spacing (Figure 26).

Figure 26: Example of coincidence detection provided by two VESDA detectors with interlaced sampling pipes

Suppression Actuation Condition: Suppression actuation will occur when both VESDA detectors reach the specified suppression actuation Fire 2 alarm threshold.

Single VESDA Detector Options 1. Dual Alarm Thresholds Option.

Coincidence detection provided by two alarm levels from a single VESDA detector.

Suppression Actuation Condition: A single VESDA detector must reach both specified alarm levels for suppression release.

Applying a delay to the second alarm level allows more time for investigation and action and safeguards against accidental suppression releases. Note the delay for suppression actuation using coincidence detection should not exceed 30 seconds for any of the coincidence detection schemes listed in this document.

2. VESDA-E VES Sampling Pipe Pair Option.

Two VES pipes (sectors) could be used in a sampling pipe pair coincidence scheme for suppression actuation.

Suppression Actuation Condition: In this case, suppression actuation will occur when two different Fire alarm conditions are issued by a minimum of two different sectors.

VESDA Ceiling (Raised Floor)/AHU Option If the fire detection system includes ceiling (or raised floor) and AHU return air grilles protection with two separate VESDA detectors, coincidence detection can be provided by these detectors.

The VESDA detector covering the AHU return air grille can be used for very early detection and as the first alarm of the coincidence detection. The Fire 2 alarm threshold of the ceiling (or raised floor) VESDA detector can be used as the second alarm.


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Suppression Actuation Condition: A good practice for this option is to utilize two different alarm levels from the ceiling (or raised floor) VESDA detector. These will form the second and third alarms for the purpose of suppression system actuation, while the Action alarm of the detector covering the AHU return air grille can be used as the first alarm. In this configuration, suppression will only be released when the third alarm of the coincidence detection is issued.

WARNING! Return air protection is effective provided the AHU is operational.

Hybrid Detection Technologies Option In cases where a IT/Communication Facility already has point (spot) type smoke detectors installed on the ceiling, it may be cost effective, in terms of capital expenditure, to use these detectors plus a VESDA system to provide the coincidence detection for suppression release actuation. An example of this option is shown below (Figure 27).

Figure 27: Example of coincidence detection with two different detection technologies

Suppression Actuation Condition: Suppression actuation will occur when any of the point (spot) type smoke detectors and the VESDA detector both reach the Fire alarm threshold.


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4 Commissioning, Service and Maintenance Once the VESDA system has been installed, its performance and pipe network integrity must be verified against the ASPIRE design file. Calculated smoke transport times for each zone should be applied conservatively. Smoke tests, as per local codes and standards are strongly recommended to check system performance for both smoke detection and suppression actuation.

Smoke transport time measurements (during commissioning and maintenance) to test the integrity of the pipe network should be done from the furthest sampling hole of the network or dedicated benchmark test point. The benchmark test point is provided beyond the last sampling hole of the pipe network and is particularly useful where the VESDA pipe network protects inaccessible or restricted areas.

The benchmark test point must remain blocked during normal operation and should be provided with an end- vent (sampling hole) for smoke transport time testing when opened. The smoke transport time from the test point might exceed the maximum transport time as long as the transport time from the furthest sampling hole is confirmed to be less than the maximum specified.

Note! The benchmark test point should bear a label identifying the detector zone, pipe number and transport time (as originally commissioned).

Where blowback systems are used to clean the interior pipes interior it is recommended that vacuum pressure is applied to prevent debris from entering the protected area.

The VESDA system shall be serviced and maintained according to the local codes and standards as well as the instructions provided in the Maintenance section of the VESDA System Design Manual.


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5 VESDA Cause and Effect Sequence When using a VESDA system for both very early warning fire detection and suppression release initiation, the following represent a suggested sequence of events following alarm conditions.

A VESDA Alert alarm condition could result in the following suggested sequence of events:

• The Alert LED lights up on the VESDA Display Module and/or a message is sent to the VSM software, if both or either are installed.

• The Alert alarm is reported to the building Fire Alarm Control Unit (FACU) via relay or High Level Integration as a supervisory condition.

• The source of the Alert alarm signal condition is investigated and the appropriate action taken.

A VESDA Action alarm condition could result in the following suggested sequence of events:

• The Action LED lights up on the VESDA Display Module and/or a message is sent to the VSM software, if both or either are installed.

• The Action alarm signal is reported via relay or High Level Integration to the building FACU as a supervisory condition.

• The FACU initiates an audible/visual signal at the FACU. • The source of the Action alarm signal is immediately investigated and the appropriate action taken.

A VESDA Fire 1 alarm condition could result in the suggested sequence of events:

• The Fire 1 LED lights up on the VESDA Display Module and/or a message is sent to the VSM software, if both or either are installed. This message indicates the location and status of the event, graphically on a floor plan, with a spoken description of the event for the benefit of on-site staff (local notification). The VSM software then sends an email and/or SMS message to a designated email address or mobile phone number to inform staff off-site of the situation (remote notification).

• The Fire 1 alarm signal is reported via relay or High Level Interface to the building FACU as a Fire 1 alarm condition.

• The FACU initiates an evacuation signal and calls out first responders.

A VESDA Fire 2 alarm condition could result in the following suggested sequence of events:

• The Fire 2 LED lights up on the VESDA detector display and/or a message is sent to the VSM software, if both or either are installed. This message indicates the location and status of the event, graphically on a floor plan, with a spoken description of the event for the benefit of on-site staff (local notification). The VSM software then sends an email and/or SMS message to a designated email address or mobile phone number to inform staff off-site of the situation (remote notification).

• The Fire 2 alarm signal is reported via relay or High Level Interface to the building FACU as a Fire 2 alarm condition.

• The FACU initiates an evacuation signal and calls out for first responders. • For suppression initiation:

o Fire 2 from any detector serving the space Initiates suppression release sequence. o Where cross-zoning is a desired or required function, Fire 2 from two or more pipe sectors (VES), or

two or more detectors serving the space may be used to initiate a suppression release sequence. o For gaseous suppression: a 30-second discharge time delay is initiated.

• Where Fan Shutdown is a desired or required function, Fire 2 signal may be used to signal the FACU to initiate this function.

www.xtralis.com Doc. No. 11782_15 June 2020

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