Determine if the Safety of the Selected Uninterruptible Power Supply UPS is Acceptable

Electronics, Instrumentation & Electrical Database

Determine if Safety of the Selected Uninterruptible Power Supply UPS is Acceptable

Continued from:

• Select the type of UPS.
  • Selecting and designing a Uninterruptible Power Supply UPS

Determine if the safety of the selected Uninterruptible Power Supply UPS is acceptable: Safety is an overriding concern of any UPS design and installation. Safety is basically governed by the electrical codes and standards as adopted by government and commercial agencies, and good judgment on the part of the design and installation team. In cases where more than one performance or safety design alternative exists, preference should be given to those that have been approved by the governmental authority having jurisdiction. Batteries pose special safety concerns for the facility manager. Safety problems associated with lead-acid batteries include spills of sulfuric acid, potential explosions from the generation of hydrogen and oxygen, and the generation of toxic gasses such as arsine (AsH3) and stibine (SbH3). All of these problems can be satisfactorily handled with the proper safety precautions. National Fire Protection Association (NFPA) 70, National Electrical Code (NEC), provides guidance on battery room ventilation. Wearing face shields and plastic/rubber aprons and gloves when handling acid is recommended to avoid chemical burns from sulfuric acid. Precautions must be routinely practiced to prevent explosions from ignition of the flammable gas mixture of hydrogen and oxygen formed during overcharge of lead-acid cells. The gas mixture is explosive when hydrogen in air exceeds 4 percent by volume. A standard practice is to set warning devices to alarm at 20 to 25 percent of this lower explosive level. Hydrogen accumulation is usually not a problem if good air circulation around a battery is present. If relatively large batteries are confined in a small room, an exhaust fan(s) should be used to constantly vent the room or should start automatically when hydrogen accumulation exceeds 20 percent of the lower explosive limit. Finally, the materials used in the battery container should be fire retardant.

Continue Determine if the availability of the selected UPS is acceptable.

References: “Joint Departments of the Army, Uninterruptible Power Supply System Selection, Installation, and Maintenance for Command, Control, Communications, Computer, Intelligence, Surveillance, and Reconnaissance (C4ISR) Facilities, 31 May 2002.”