Volume 2, Issue 10 (November 2005)
Fire Testing of Electrical and Optical Fiber Cables for Transportation Vehicles, Especially in North America
Cables for transmission of power and data are a large, and growing, part of the fuel load in public transportation vehicles. Unfortunately, the fire performance of electric cables has usually been neglected or based only on semi-mandatory guidelines of relatively low severity. Furthermore, optical fiber cables have usually been ignored. This paper discusses the most recent approaches taken by the various regulatory authorities in the US (US Coast Guard [USCG], Federal Aviation Administration [FAA], Federal Railroad Administration [FRA], and Federal Transit Administration [FTA]), together with the work of the applicable standards developing organizations (the National Fire Protection Association [NFPA] and the International Maritime Organization [IMO]).
The US Coast Guard regulates all ships in US ports, but, as a signatory to the International Convention of Safety to Life at Sea (SOLAS), the International Maritime Organization regulates US ships going into international waters. Ships that do not go into international waters (including those that just cross rivers or lakes and those that operate in amusement parks) do not have to meet SOLAS requirements and can meet USCG requirements only or can meet the voluntary requirements contained in NFPA 301, Code for Safety to Life from Fire on Merchant Vessels. While SOLAS has very mild regulatory requirements for cabling, NFPA 301 has a minimum requirement for cables to meet the vertical cable fire test in CSA FT4 or UL 1581-1164 (a fairly severe test). Cables meeting more severe fire test requirements are also permitted to be used as replacement for these tests.
The Federal Railroad Administration regulates intercity trains as well as trains that cross state lines. FRA does not have required cable fire tests for cables. However, NFPA 130, Standard for Fixed Guideway Transit and Passenger Rail Systems, has as a minimum fire test requirement of a slightly milder vertical cable tray fire test for cables, the one in UL 1581–1160, but a smoke obscuration test is also required. Again, cables meeting more severe fire test requirements are also permitted to be used as replacement for these tests. NFPA 130 is widely used by many rail authorities, both in the US and abroad (particularly Canada and the Far East), as it is more severe than the FRA rules.
The Federal Transit Administration provides guidelines and no requirements, and its guidelines apply to subways and suburban trains that do not cross state lines. The guidelines do not include any information on fire safety of cables. NFPA 130 also applies to subways and all trains, of course.
The Federal Aviation Administration regulates both the wiring that is placed into airplanes by air frame manufacturers (those who build the airplanes) and the one put in afterwards by airlines (usually for entertainment systems). The requirements are the same for both: a small 60° angle Bunsen burner test. The issue that needs to be pointed out, however, is that the cabling used by air frame manufacturers has a fire performance that is greatly superior to that required to meet the test, while the cabling used in entertainment systems is often barely able to meet the fire test and may be unsuitable from the point of view of fire safety. FAA is aware of this and is undertaking a program to develop an adequate fire test for all cabling in airplanes.
NFPA has a committee, Hazard and Risk of Contents and Furnishings, which is developing a Guide on Methods for Evaluating Fire Hazard and Fire Risk of Vehicular Furnishings, to be called NFPA 556, which will address cabling. The Fire Protection Research Foundation is also looking into this issue with their new Research Advisory Council on Fire and Transportation Vehicles.
In summary, this is an area where fire safety is a potential concern, but where abundant activity is taking place.