Fonte (Source): Consulting-Specifying Engineers
Por (By): John Yoon, LEED AP ID+C, McGuire Engineers Inc., Chicago
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In the eyes of life safety codes, the value of a building’s contents is never greater than the safety of the public. However, when uninterruptible power supply (UPS) systems are specified for data centers, uptime requirements are often the emphasis and this guiding principal is lost.
The batteries associated with UPS systems represent an unusual hazard. Remember that lead-acid batteries are devices that store incredible amounts of energy in a chemical form. In the course of normal operation, all lead-acid batteries generate hydrogen gas. Hydrogen gas is unusually reactive and reaches explosive concentrations at 4% by volume. This minimum concentration is referred as the lower explosive limit (LEL). While certain designs, such as valve-regulated lead-acid (VRLA) batteries, dramatically reduce the amount of hydrogen released into the environment (as compared with traditional wet/flooded cell batteries) during normal charging and discharge cycles, there are still code requirements to address this potential hydrogen hazard.
Two primary fire codes (International Fire Code (IFC) and NFPA 1: Fire Code) define the appropriate construction and supporting infrastructure that must be provided for storage battery rooms. These requirements often are overlooked because they are addressed in codes that aren’t regularly reviewed by electrical and mechanical engineers. It should be noted that emerging UPS battery technologies, such as lithium-ion (Li-ion), are also included.
The following is a short summary of the requirements in these codes for stationary storage battery systems. Please note that these two codes are not interchangeable.
Confirming with the AHJ is necessary to see which code has been adopted.
IFC 2015, Section 608
Section 608 applies to stationary storage battery systems having an electrolyte capacity of more than 50 gal for flooded lead-acid, nickel-cadmium (Ni-Cd), and VRLA or more than 1,000 lb for Li-ion and lithium-metal-polymer used for facility standby power, emergency power, or UPS.
As defined by IFC 608.6.1, room ventilation:
Ventilation shall be provided in accordance with the International Mechanical Code and the following:
- For flooded lead-acid, flooded Ni-Cd, and VRLA batteries, the ventilation system shall be designed to limit the maximum concentration of hydrogen to 1% of the total volume of the room.
- Continuous ventilation shall be provided at a rate of not less than 1 cfm/sq ft of floor area of the room.
Exception: Li-ion and lithium-metal-polymer batteries shall not require additional ventilation beyond that which would normally be required for human occupancy of the space in accordance with the International Mechanical Code.
The two ventilation requirements are not an “either/or” permissive option. This is contrary to the requirements of NFPA 1.
Other generic provisions of IFC Section 608 include the following:
- Must prevent access to unauthorized personnel. This can be accomplished by either locating in separate room or in noncombustible cabinets. They may be located in the same room with the equipment they support.
- Must provide spill control and neutralization for batteries with free-flowing electrolyte (i.e., flooded cell batteries). No specific threshold is given, but it is assumed to apply where greater than 50 gal. Not required for VRLA or lithium.
- Must have proper supervision of ventilation system.
- Must have signage on door.
- Must have smoke detection.
- Requires thermal runaway protection for VRLA batteries.
- Li-ion and lithium-metal batteries don’t require ventilation.
NFPA 1-2015, Chapter 52
NFPA 1 is not as frequently adopted by municipalities as the IFC. While the basic requirements of NFPA 1 generally parallel those of the IFC, the technical provisions within NFPA 1 do have significant difference that can impacted the design of related battery ventilation systems. These requirements are as follows:
Chapter 52 applies to stationary storage battery systems having an electrolyte capacity of more than 100 gal in sprinklered buildings or 50 gal in nonsprinklered buildings for flooded lead-acid, Ni-Cd, and VRLA batteries or 1,000 lbs for Li-ion and lithium-metal-polymer batteries used for facility standby power, emergency power, or UPS. This is a significantly lower threshold than that in IFC.
NFPA 1, 52.3.6 Ventilation indicates:
For flooded lead-acid, flooded Ni-Cd, and VRLA batteries, ventilation shall be provided for rooms and cabinets in accordance with the International Mechanical Code and one of the following:
- The ventilation system shall be designed to limit the maximum concentration of hydrogen to 1% of the total volume of the room during the worst-case event of simultaneous “boost” charging of all the batteries in accordance with nationally recognized standards.
- Continuous ventilation shall be provided at a rate of not less than 1 cfm/sq ft of floor area of the room or cabinet.
This language allows for significantly more flexibility than IFC. Other provisions of Chapter 52 include the following, which are not addressed in the IFC:
- In assembly, educational, detention, health care, day care, etc., battery systems shall be located in a room separate from other portions of the building and be 2-hour fire-rated.
- Thermal runaway protection is required for lithium batteries.
- Spill control is required where there are more than 55 gal in individual vessels or an aggregate capacity of greater than 1,000 gal.
- The battery environment shall be controlled or analyzed to maintain temperatures in a safe operating range for the specific battery technology used. In the case of VRLA batteries, they’re typically rated for an ambient of 77˚F. Although it is not specifically stated, this effectively requires that air conditioning be provided for most battery rooms.