Positive Attachment Defined in Building Codes
The requirement for seismic restraint of lighting fixtures within suspended ceiling systems was originally developed by DSA (originally known as OSA) based on observations of damaged ceilings from the 1971 San Fernando earthquake. The principles of these guidelines were subsequently copied by CISCA (Ceilings & Interior Systems Construction Association) and adopted into UBC (Uniform Building Code), IBC (International Building Code), and NEC (National Electrical Code) codes.
A properly attachment device will allow the lighting fixture to remain attached to the suspended ceiling grid in an earthquake (shown at right).
The Code prescription for Positive Attachment:
UBC Section 25-2 states, "All lighting fixtures shall be positively attached to the suspended ceiling system. The attachment device shall have a capacity of 100 percent of the lighting fixture weight acting in any direction”.
The problem with Section 25-2 is that it does not provide specific structural engineering description of how to satisfy the intent of this clause. Some of the unclear issues are:
- What is the minimum number of attachment points?
- What is the minimum load capacity of each attachment device?
- What is the minimum expected seismic performance of the lighting fixture / suspended ceiling system together with the attachment device to protect the safety of occupants?
This clause does not take into account the structural integrity of the lighting fixture. If the lighting fixture breaks apart and the florescent tubes fall on the floor due to the restraint provided by the positive attachment devices, would it properly protect the occupants' safety as intended?
In 2002, ICC (International Code Council) published AC 184 to properly define “positive attachment”.
In the 1990s, it became clear to ICC that a more scientific definition was required to ensure that the industry would adhere to the intent of the original UBC and CISCA code requirements to protect public safety.
ICC published the acceptance criteria AC184 to clearly outline the static and dynamic testing requirements for devices to be acceptable for use to meet the “positive attachment” requirement