The 2003 Edition of NFPA 130 first addressed the issues of smoke encroaching on non-incident trains on the downstream side of a fire. NFPA 130, Section 7.2.5, states “The design and operation of the signaling system, traction power blocks, and ventilation system shall be coordinated to match the total number of trains that could be between ventilation shafts during an emergency.”
The 2007 Edition further explained the intent of the Standard in the annex materials. Section A.7.2.5, states “Transition from fixed-block to moving-block (cab-based or communication-based) signaling is being made by many properties to increase train throughputs during rush hour operation. Ventilation zones are fixed elements, and the number of trains allowed in a single zone affects both ventilation plant requirements and the effectiveness of the ventilation response. Traction power blocks are fixed elements and affect the ability to extract non-incident-trains from the incident ventilation zone. Signal system track circuits are fixed elements and affect the ability to determine the location of incident and non-incident trains in the incident ventilation zone.
Signal system reversing capability and rapidness of executing a reversal in an emergency are key to the effective extraction of non-incident trains. Due to the potential for a valid incident ventilation response to move smoke past (an engulf) a non-incident train, the best protection to passengers is to allow no more than one train in a ventilation zone. Failing that, there should be a viable extraction capability to remove non-incident trains in the same time frame as the activation of the ventilation response. This extraction requires coordination of the three system elements in terms of design and operation. Non-incident trains should be capable of being located and removed from the incident area before the de-energization of the traction power prevents train movement for an extended period or the operation of the ventilation system in response to the fire incident involves the trains in the incident.
Examples of the provisions necessary to accomplish this capability are the inclusion of traction power segmentation zones within ventilation zones and the inclusion of sufficiently short track signal circuit lengths to ensure all trains are accurately located.”
Section 7.2.5 does not specify one train per vent zone. It states the design shall be coordinated to match the total number of trains that could be between ventilation shafts during an emergency. Section A.7.2.5 offers a remedial action if the train throughput rate (trains per hour) dictates the presence of more than one train in a vent zone. The remediation involves :
- A viable extraction of non-incident trains in the same time frame as the activation of the ventilation response, and
- Non-incident trains should be capable of being located and removed or re-routed from the incident vent zone before the traction power system is de-energized.
Transit and rail agencies typically develop strict sets of procedures to govern the backing of train movements because of safety reason. These procedures would also tend to elongate the time needed to back trains during a fire emergency. The extraction of non‐incident trains cannot be easily accomplished in the same time frame as the activation of the ventilation response. Therefore, the best protection to passengers and crew members is to allow no more than one train in a vent zone.
The one train per vent zone can be achieved without significant cost penalty for short tunnels and long train headways. However, for long tunnels and short train headways, capital construction costs and/or train throughput would be affected. It has been demonstrated that, without adversely impacting train throughput and construction costs, cost-effective tunnel ventilation systems are feasible to achieve one train per vent zone. Further information, please refer to the Post on “Ventilation Concepts for Meeting One Train Per Vent Zone“.
(featured image from Andrew Louie)