BLOWING OFF EXTINGUISHING GAS CAN AFFECT HARD DISKS

BLOWING OFF EXTINGUISHING GAS CAN AFFECT HARD DISKS 

Extinguishing gas installations have been installed on a large scale in DVR, NVR, NAS, Graphic Workstation, computer, IT, data storage rooms over the past decades. The design of these systems and components meet the relevant product and system standards, such as EN, ISO, and NFPA. These installations also meet national laws and regulations and / or insurance requirements. Recurring inspections and maintenance requirements of the aforementioned standards ensure the reliable operation of these fire extinguishing systems throughout their lifespan. The purpose of a fire extinguishing system in such a room is to quickly detect and extinguish a fire. The derived objective is to cause the least possible collateral damage and / or downtime. This ensures continuity and protects data and equipment against damage.

In recent years, some failures of hard disks have been known. Disturbances that may result from blowing off extinguishing gas in the event of a fire or test in the room concerned. This concerns the corresponding high-frequency noise level. The problems described relate only to high-pressure systems: Inergas, Argonite, Inergen, etc. with and without I-Flow technology.

Tests conducted under the guidance of the European Association in collaboration with test laboratories and suppliers of hard disks, learn that:

• A sound pressure level approaching 110 decibels can interrupt the operation of a hard disk and lead to permanent failure of the hard disk;
• The sound pressure during the extinguishing of the extinguishing gas when the fire extinguishing system or acoustic sources (alarms) are activated can influence the hard disks;
• Although the phenomenon occurs with all brands of hard disks, there are differences in the extent of the effect on the different types of hard disks. “Enterprise class” hard drives were less sensitive to these tests than the “near-line-class” hard drives.

THE FOLLOWING WAS NOTED WITH REGARD TO THE EFFECTS:

• The use of a damper-blow nozzle combination has positive influences;
• The damper-blow nozzle combination should not be aimed at the hard disk;
• The distance between the silencer nozzle assembly and the hard disk must be as large as possible, as permitted within the applicable standards;
• Reducing noise levels of alarms has positive influences. Mechanical-pneumatic alarms are more often the cause than electronic alarms. Mechanical-pneumatic alarms are not used in the Netherlands for extinguishing gas systems in IT rooms (in contrast to Germany where this is frequently the case);
• Installing discs in soundproof enclosures reduces observed effects;
• Use patented software to minimize the tolerance of hard drives.

WHAT NOW:

If there are concerns about the vulnerability of the hard disk, we recommend a controlled ‘shut down’ where the hard disks are first switched off before the extinguishing gas system is activated and with certain functional tests. The latest generation of Solid State Drives (SSDs) are, due to the lack of mechanical components, far less susceptible to external influences.

In addition, the placement of dampers on the blow nozzle or a damper-blow nozzle combination is recommended. In this case, the manufacturer issues a substantiated guarantee of the occurring sound pressure at the nozzle during an extinguishing. If there are very outdated systems or more expensive maintenance moments (such as inspections of cylinders), replacement with modern systems can also be a good alternative.

We like to think along with you to see the possibilities in your situation. Please contact our Service department by email ssaintegrate@gmail.com. Of course you can also contact your own account manager, contact person or project manager.

EOL Resistor not a Termination Resistor

Early security systems used simple electrical circuits to monitor the status of doors and windows. The circuit was either closed or open, and therefore returned full voltage or no voltage at all to the control panel; that was all the system wanted or needed to know. Although such circuits are still in use today, the digital age gave manufacturers the opportunity to make systems more secure.

A resistor is a small semiconductor which resists the flow of electrical current. The current is permitted to flow, but is reduced by the value of the resistor. If a resistor is connected, in series, with a sensor on an alarm circuit, then the control panel no longer sees full voltage across the circuit, but rather a reduced voltage, when the circuit is closed. Now there are three possible conditions for the control to measure: full open-circuit voltage (if the circuit is open), reduced voltage (if the circuit is closed and secure), and no voltage if the wiring has been compromised. For if the two sides of the circuit are making contact at some point between the control and the resistor, the current has a shortcut back to the control, thus bypassing the resistor. The control will see this no voltage (or very low voltage) as a fault and will alert the user.

In fire alarm and security systems, at the end of the input circuit (Initiating Line Circuit or IDC), and at the end of the output circuit (Notification Appliance Circuit or NAC), there's an End-of-Line Resistor. 

Both the Terminating Resistor and the End-of-Line Resistor (EOL) are across the conductors at the end of the circuit. 

The difference between the two types of resistor, though, is not where they're at or even what they're made out of. They're both at the end of the line, and both across the conductors. They can even come out of the same package from the store or distributor. 

The difference between the two is why they're installed at the end of the line. 

Terminating Resistor

In signal carrying systems, especially between equipment like between the TV camera and the video recorder (Closed Circuit TV or CCTV), or an RF amplifier for a Master Antenna TV (MATV) system and the TV set, there's a Terminating Resistor. 

On a Video Input, inside the DVR (Digital Video Recorder or Security Recorder) there's a Terminating Resistor. 

With Master Antenna TV (MATV), the Terminating Resistor is at the last "tap" when several taps are used in a single line from the amplifier. 

When the TV set is at the end of the line for the MATV system, inside the TV set there's a Terminating Resistor. 

For a true RS485 communication control circuit, there's Terminating Resistors at each end of the daisy-chain. 

Purpose of the Terminating Resistor

A Terminating Resistor is a Signal Quality component. It is used to soak up an AC signal, preventing reflections or ghosts on the line. 

It takes time for signals to travel along wire, and the energy of the signal cannot be created or destroyed; it has to go somewhere. At the end of the line where the wires end, if the wire is just cut off, the signal hits the end of the line and bounces straight back. 

If the wires at the end are shorted together to prevent the bouncing straight back, the signal takes a U-turn and returns in reverse voltage. 

Because of the time it takes for the signal to travel to the end of the wire and back, the bounced back signal is an extra, unwanted signal on the line. It degrades the video or control signals, or if the wire is long enough even returns as an extra erroneous video or control signal. 

The value of the Terminating Resistor is chosen very carefully to be able to soak up this signal when it reaches the end of the line so the signal doesn't bounce back. 

End-OF-Line Resistor

The End-of-Line Resistor used in fire alarm systems and security systems may look the same as a Terminating Resistor, however the function of the End-of-Line Resistor is completely different. 

The "End-of-Line Resistor" confirms that the wiring in a building remains undamaged. It's across the end of all the wire in each pair of wires (loop) for all inputs (Initiating Device Circuit or IDC) and outputs (Notification Appliance Circuit or NAC). 

Purpose of the End-of-Line Resistor

As opposed to the terminating resistor, which is there to prevent signal reflections, the End-of-Line Resistor is a Life-Safety and Property Protection component. 

It's important to understand that the "signals" used in fire alarm systems are DC, either on or off, not AC, which carries information like video or data. 

Because there's no AC, there are no reflections from the end of the loop; the End-of-Line Resistor is used to pass DC current. 

The only purpose is to pass a small supervision current so the fire alarm or security panel can "look" at the wire; if the supervision current stops, the stoppage can be reported immediately, and the trouble fixed, before there is a real fire. 

The End-of-Line Resistor versus the Terminating Resistor

So the Terminating Resistor of RS485 control wiring or coax cable is used to soak up AC signals, while the End-of-Line Resistor of the fire alarm or security system loop is used to pass DC current.