Preservation Note 45

Air Sampling (Aspirating) Fire Detection Systems

Special Construction

October-99

Fire Alarm and Detection Systems-13850

New advances in fire detection technology are making fire protection
systems less intrusive in historic buildings. Air sampling, or
aspirating, fire detection systems represent new technology that can
offer increased protection by providing earlier detection and a
potential to reduce the physical and aesthetic impact of fire protection
upgrades in historic buildings.

Air sampling systems consist of small components which can be installed
with minimal visual and structural impact. The small sampling tubes used
to collect air can be concealed in unobtrusive places like light
fixtures, ledges, or ornamental ceilings, which makes these systems good
choices for historic properties.

Since air sampling systems are generally costlier than conventional
detection systems, and have limitations, at this time their use in NCR
public buildings is best limited to particular spaces where their
capabilities offer exceptional benefits in reduced visual impact or
damage to ornamental finishes. Consider use for large spaces with high
ceilings or spaces with ornamental ceilings and upper wall surfaces.
These systems can be combined with other types of detection and
suppression systems.

Detection Advantages

In historic structures, early detection is critical to avoid extensive
damage or destruction of a significant building and its contents, in
addition to the life safety concerns. Fire must be detected early in the
smoldering, incipient stage before active flaming occurs. Once flames
have occurred it is too late, serious damage will occur from the flames
and then from the water used to extinguish the fire.

Fires have four stages: incipient, visible smoke, flame, and heat. Smoke
at the incipient stage of a fire is low in density, below the detection
level of conventional smoke detectors. Also, early smoke does not always
rise to reach ceiling-mounted detectors, especially in large open spaces
with high ceilings.

Air sampling (aspirating) fire detection systems offer greater
sensitivity and speed than conventional detectors. Location of the air
sampling tubes is not limited to the ceiling. The exposed tubes are
small, easy to conceal, and can be located below the ceiling level to
pick up smoke earlier, before it rises. The systems can detect invisible
particles generated during the pre-combustion stage of a fire, at levels
of obscuration as low as 0.003% per foot, as compared to 3% per foot
sensitivity of a typical spot-type photoelectric smoke detector.
Manufacturers\' literature claims they are up to 1000 times more
sensitive than conventional ionization or photoelectric type smoke
detectors. This early warning capacity makes it a particularly
attractive alternative for historic structures and large open areas such
as atriums, open stairs, and two story spaces.

Aesthetic Advantages

Conventional photoelectric and ionization fire detectors (point
detectors) are designed to detect fire at a specific location, requiring
a number of properly placed smoke detectors to cover a large area. These
units are fairly large and are difficult to conceal. Decorative
interiors, especially ceilings, in historically significant buildings
make it difficult to install traditional smoke detectors without taking
away from the historic character and materials of the space.

Air sampling detection systems offer less obtrusive installation with
minimal disturbance and damage to architectural and historic features
and spaces. Components are small, easy to conceal, can be placed in a
wide variety of areas, and provide wide coverage. The only elements
visible in a space are the tiny, clear plastic sampling tubes which can
be concealed in light fixtures, ledges, and ornamental ceilings,
allowing wider dispersal of the detection system with minimal
architectural impact. The piping is flexible and can fit in almost any
space. The actual detector can be located in a different room. A single
detector is designed to monitor up to 20,000 square feet. It would take
20 point detectors to cover the same area.

How Air Sampling Fire Detection Works

An air sampling or aspirating-type fire detection system is a
self-contained smoke detection package comprised of five primary
components: an air sampling system, aspiration system, filter assembly,
detector, and control system. It uses a network of pipes to continuously
draw air samples and direct them to a central smoke detector.

The system operates with a network of sampling pipes which extend into
the protected area. The pipes have an inside diameter of 1/2\", 3/4\",
or 1\" and are usually made of thermoplastic material. An internal
aspirator continuously draws air into the piping network. To filter out
airborne dust and debris particles, which helps to eliminate false
readings, the systems use either a filter assembly or laser particle
counting technology.

The air samples then pass into the detection chamber for analysis. Here
the air is illuminated by either a laser light or broad-spectrum xenon
light source where the beam bounces light off small particles released
by combustible materials. Very sensitive receivers detect the light,
scattered by smoke particles. The receivers convert the light energy
into an electronic signal, representing the level of smoke in the air
sample, and send the signal to the control system for processing.

The control system receives and processes the information. Smoke
obscuration levels are presented graphically on a bar graph display
indicating three smoke level thresholds: alert, action, and fire. When
appropriate, the control module reports trouble and activates the alarm.
Alarms can be reported locally or to an off-site location. The control
module stores a history log of past smoke levels and events.

Product Information

Currently, there are two primary manufacturers of air sampling fire
detection systems. While each system works a bit differently, they
function in very similar ways.

Kidde-Fenwal, Inc. produces Fenwal\'s AnaLASER High Sensitivity Smoke
Detection System (HSSD). The AnaLASER 50 covers areas up to 5,000 square
feet, the AnaLASER 100 covers up to 10,000 square feet, and the 200SI
covers up to 20,000 square feet. For product information, contact the
company at:

Fenwal Protection Systems

Kidde-Fenwal, Inc.

400 Main Street

Ashland, MA 01721

Phone number: 508-881-2000

Fax number: 508-881-8920

Email: info@kidde-fenwal.com

Web page: http://www.kidde-fenwal.com

Vision Systems produces the VESDA (Very Early Smoke Detection Apparatus)
Air Sampling System, including the VESDA LaserPLUS, which is designed
and approved to monitor up to 20,000 square feet, and the VESDA
LaserCOMPACT for use in smaller areas. For product information, contact
the company at:

Vision Systems Inc. - VESDA

35 Pond Park Road

Hingham, MA 02043

Phone number: 617-740-2223

Toll-free phone number: 800-229-4434

Fax number: 617-740-4433

Web page: http://www.vsl.com.au/vesda

Installation Requirements

The design and installation of an air sampling detection system requires
the services of a certified Fire Alarm Specialist thoroughly experienced
in the installation of these systems.

All fire detection systems should comply with National Fire Protection
Association (NFPA) standards. Refer to:

NFPA 914 Recommended Practice for Fire Protection in Historic Structures
(1994)

NFPA 914 Standard for Fire Protection in Historic Structures (draft of
2001 edition available)

NFPA 909 Standard for the Protection of Cultural Resource Facilities
(1997).

Refer to related Preservation Notes available from the General Services
Administration, National Capital Region (GSA/NCR), Historic Preservation
office or online at the GSA/NCR site at
http://ncr.gsa.gov/historicpreservation/note.asp. Related titles
include:

#10 - Fire Alarm Installation

#20 - Sprinkler Systems: Design Guidelines For Historic Buildings

#22 - Meeting Fire Rated Corridor Separation Requirement For Special Use
Office Space

#34 - Fire Safety Retrofitting Policy And Related Historic Preservation
Standards.

Also, refer to the related Outline Specifications available from the
GSA/NCR Preservation Office or online at the GSA/NCR site at
http://ncr.gsa.gov/historicpreservation/specs.asp. Related titles
include:

01 General Requirements - 01091 Reference Standards - Fire Safety
Retrofitting Guidelines For Historic Buildings

15 Mechanical - 15300 Fire Protection - Design Guidelines For Installing
Sprinkler Systems In Historic Buildings

16 Electrical - 16721 Fire Alarm & Smoke Detection Systems - Guidelines
For Installing Fire Alarms In Historic Buildings.