NIST engineer Kate Remley holds two Personal Alert Safety System (PASS) devices with wireless alarm capability. Photo: Paul Trantow/Altitude Arts |
Wireless emergency safety equipment could save lives—if
signals are transmitted reliably. But few performance standards exist. Now,
tests at NIST are helping to ensure that alarm beacons for firefighters and
other emergency responders will operate reliably in the presence of other
wireless devices.
NIST is providing technical support for industry consensus
standards by developing test methods to evaluate how well these devices work
under realistic conditions. The latest NIST study focused on interference
between Personal Alert Safety Systems (PASS) with wireless alarm capability,
and radio-frequency identification (RFID) systems. The methods developed in the
study can test interference in other wireless devices such as radios,
hands-free cell phone headsets, local area networks, and urban search and
rescue robots.
PASS devices sense movement and activate an alarm if a
firefighter remains motionless for too long. Newer PASS systems also have a
wireless link connecting incident command base stations and portable units,
allowing emergency recall signals to be sent to firefighters or “firefighter
down” alarms to be sent to the base. Because firefighters also may carry RFID
tags for location tracking, or may be in warehouses or other buildings using
RFID inventory systems, there is potential for significant interference.
“Every wireless device will fail given strong enough
interference,” says NIST project leader Kate Remley. “The question is the level
at which the device fails. Our goal is to develop lab-based test methods to
quantify the level of interference at which PASS units fail so we can help
ensure they operate reliably.”
The NIST research measured interference between “frequency
hopping” PASS and RFID systems operating in similar frequency bands. Results
show that, when signals are weak due to environmental or other conditions, a
portable PASS unit’s receipt of an alarm from its base station can be delayed
or fail even without interference, and becomes more likely to fail in the presence
of only moderate RFID interference. Strong interference caused longer and
variable delays that sometimes exceeded a minute, defined by the researchers as
signal failure. NIST researchers also found that an RFID system can be less
reliable when the PASS unit is nearby.
The NIST tests involved measuring the total output power of
each system in a test chamber and then isolating the systems in different labs
for the interference tests. The portable PASS device and RFID tag and reader
were placed in a test chamber, while the PASS base station was in a separate
room. Researchers evaluated performance at various levels of signal strength
and interference.
NIST is working with the National Fire Protection
Association, which will consider adopting the NIST tests as part of revised
PASS performance standards. An NFPA technical committee on electronic safety
equipment will soon consider the wording of a draft standard, and after a
public comment period, the standards could be approved by 2013. At that point,
manufacturers would need to show that their PASS devices pass the tests.
