CIRCUIT INTEGRITY CABLES:

Typical life safety critical circuits in a high-rise building. Typical Applications of 2-hour fire-rated Fire Alarm and Power cables that meet stringent requirements for Life-Safety circuits Emergency Power Supply Firefighter's Elevator Fire Pumps Fire Alarm Voice Communication & Fire fighter's Handsets Emergency Power for Lighting Pressurization Fans & Smoke Dampers Smoke Venting Fans Typical locations requiring circuit integrity emergency power feeders include: High-rise buildings Hospitals and other institutions Historic buildings Tunnels and subways Airports, stadiums, hotels, banks, etc.

 

However, while mineral insulated (MI) cable was used for fire protection of life safety systems for ships, tunnels, and buildings that were highly engineered or of an historic or prestigious nature, it was not the first choice for high-rise buildings. Instead, life safety systems were mostly met by traditional "construction methods" of either encasing cabling in concrete or building gypsum board enclosures or shaftways (or occasionally employing a "wrap" system i.e. putting a thermal barrier between the conductors and the fire).  Masonry walls were specified in 1931 for the shaftways of the Empire State Building - assumed to be the first modern high-rise - that housed elevators, stairwells and mechanical utilities. Gypsum tiles were chosen for the Merchandise Mart in Chicago in the same year. In the 1960s, as the demand for lighter and more elastic shaft wall systems grew, gypsum panel wall systems started to be more widely used.

In late 1999, fire-rated polymer insulated cables became available. This presented a sea change in the status quo as improved technology significantly expanded the options for meeting fire code requirements. Specially designed polymer insulation changes into hard insulating ash under fire conditions, thus allowing electrical conductors to remain isolated from one another. With the advent of this new technology, a new breed of cable - fire-rated polymer insulated power and fire alarm cable - and a new alternative to construction methods was created.

"The fire-rated cable market has expanded at a rapid rate since the introduction of polymeric fire resistant cables," says Barry O'Connell, P. Eng., of Tyco Thermal Controls. "This is not because of an increase in construction, but because of increased choices of product and manufacturer for specifiers, and awareness of the advantages of fire-rated cables over construction methods of fire protecting cables."

As more manufacturers became involved in production, today's fire-rated cables come in a variety of styles that appear and install like conventional conduit cables, armored cables and fire alarm cables. Usually competitively priced, these cables are expanding the use of fire-rated cables as a replacement for construction methods.

Fire Protection of Life Safety Circuits: Codes and Test 

Since life safety is the most important consideration for all projects, fire protection of life safety electrical circuits has long been mandated by code. Over the decades, codes have been updated, mostly in response to lessons learned from investigations into the causes of fires. Municipalities are also taking fire code compliance more seriously. Following up on the August 2007 deaths of two firemen killed while fighting a fire at 130 Liberty Street, the former Deutsche Bank building at the World Trade Center site that was being demolished, New York City has cracked down on fire code violations. In the 12 months preceding June 2008, 225 people have been arrested on charges of failing to appear in court to answer outstanding criminal summonses for fire code violations.

Most states and Canadian provinces adopt a model code, such as the International Building Code (IBC) and the National Building Code (Canada) as the basis for their own code. Code requirements for life safety circuits in the United States are provided by the Fire Protection Association (NFPA) and the National Electric Code (NEC). However, the type of fire protection for critical life safety circuits is not specified by code.