Fire-Life Safety and System Integration: The Functional Mode Table

A high-level computer program for tunnel operation during emergency events, the FMT automates responses required to manage or prevent emergency situations.

Introduction 

A fire or other emergency situation in a tunnel environment can be a serious threat to human life and the infrastructure. One of the main tasks of the fire-life safety (FLS) engineer is to develop a response strategy to manage or prevent such events. The strategy will frequently rely on many sub-systems such as ventilation, lighting and signage, traffic management, alarms, operator responses and coordination, and communication with emergency services agencies (e.g., the fire department). The harmonious and correct operation of the sub-systems is essential to protecting life and infrastructure during an incident; clear and concise system integration is needed to achieve this goal.

Figure 1– The “V” diagram and the Functional Mode Table relationshipFigure 2 – Functional Mode Table concept outline

Integration is not a new concept as exemplified by the “V” diagram (see Figure 1) which is a well-known concept in systems engineering. However, FLS relies on more than just systems integration; it is also necessary to combine the emergency incident plans with the design concepts and operator training. The concept of the Functional Mode Table (FMT) is proposed herein as a tool to assist in this exercise.

The FMT, in principle, is a high-level computer program for tunnel operation during a given emergency scenario. It is a matrix of instructions that spells out in a detail how each sub-system must respond for a given emergency incident. It is based on an incident type, the means of detection, and the sub-system responses required (see Figure 2).

The goal of the FMT is to assure that all major players in the tunnel’s fire-life safety – the FLS engineer, the implementation engineers, the operator, and emergency services workers – will work to a common framework, thereby improving implementation, commissioning, training, thereby maximizing the probability of a favorable outcome if an emergency occurs. Subsequent system responses for an incident can be pre-programmed using the FMT, reducing the complexity and burden placed on the tunnel operator. 

Case Study – An Urban Road Tunnel 

Table 1 – Sub-system response for a road tunnel fire

To illustrate the FMT concept, a virtual case study of an urban road tunnel several kilometers long is used. For the present discussion the tunnel is taken to have the following principal system features:

• Unidirectional traffic;
• Longitudinal ventilation;
• Egress points at 200 meter spacing (to an adjacent tunnel);
• CCTV system;
• Fixed fire fighting system;
• Communications (phones, public address), lighting, traffic controls; and
• Full-time tunnel operator.

The ventilation system plays a major role in life-safety, directing smoke downstream of the fire so that people upstream are protected (see Figure 3). However, the ventilation system alone will not necessarily produce a favorable outcome; a successful outcome needs several provisions to operate correctly. During a major incident, ventilation operation is only one of several important steps that need to be taken, as explained in Table 1.

Figure 3 – Road tunnel fire-life safety concept

Overcoming Operational Complexity – The FMT and a One Button Response 

Table 1 outlines a number of sub-systems required to operate during an emergency, and a major tunnel will typically have a full-time and well-trained operator. However, it is not reasonable to expect the operator to manually perform all of the actions required for the following reasons:

• Operators are typically not engineers and therefore not versed in tunnel systems design.
• During an emergency an operator’s capacity to perform sophisticated system adjustments may be limited by the enormous flow of information among the operator, the motorists, and the emergency agencies. An operator’s attention becomes focused on specific events and as a result may fail to take into account the broader situation, a condition referred to as “attention tunneling”.
• Emergencies do not occur frequently and so the operator has limited practice at performing the required actions.
• Emergency situations are high stress events within the control room. Designers of the systems need to be mindful of the possibility for an operator to “lock up” which could further delay the correct response. 

System integration and programming of the control system to automate much of the incident response is required for the essential actions to take place. It is critical that the responses required with each sub-system for defined emergency scenarios have a simple yet methodical procedure. The FMT provides this procedure. It is the connection among the fire safety engineer, the programmers developing the control system’s detailed automatic routines, the system hardware, and the tunnel operator (see Figure 4). The FMT also forms a critical link at the design level (see Figure 5).

Figure 4 – Functional Mode Table links

Figure 5 – Functional Mode Table design links

Given the number and complexity of tunnel systems, the burden on the tunnel operator needs to be minimized. If the operator has “too many clicks” to initiate at his/ her interface, it will slow the response and increase the chances of errors. In the “one button response” the systems are configured in a way that, once the operator provides essential information, a pre-programmed response is enacted. The FMT provides a framework for this and a simple example is provided in Table 2. Generating a one button response requires that all stakeholders in the emergency response system are aware of the realistic information available during an emergency situation and the order of actions to be taken. As fire-life safety engineers, it is our responsibility not only to define the spectrum of data and available actions, but also to define the data with language, terminology, and structured presentation that is easily communicated and understood by other stakeholders. This task is challenging but not out of reach.

Table 2 – Functional mode table example (showing a limited number of incidents and devices)

For example, with a well-designed FMT and incident response plan, during a fire in a road tunnel the operator would need to answer some basic questions at each stage in order to then activate the physical tunnel systems. Table 3 provides a simplified account of the response stages, questions, and system actions.

The outline of questions in Table 3 minimizes the amount of information that the operator must give, thus reducing the time it takes for a response and maximizing the chances that the correct system actions will be taken and all the essential sub-systems will be activated. 

The operator may need to make adjustments later, possibly manual adjustments, but with this framework the initial response and activation of critical systems for fire-life safety are certain.

The example presented assumes an automated control system that will activate all appropriate systems. However, in preliminary discussion with tunnel operators that work with antiquated or ill-equipped control systems, a similar approach can be taken with the use of clearly defined hard-copy instructions. In summary, the format, language, and terminology of the FMT are critical for operator interpretation and response in an actual emergency situation.

Table 3 – Operator response concept – “one button” concept

Fire-Life Safety Standards 

NFPA 502: Standard for Road Tunnels, Bridges, and Other Limited Access Highways 2014 edition requires that a road tunnel have an emergency response plan, developed by the agency responsible for operating the tunnel. The standard requires that the plan state how the various systems will operate for a given incident. The FMT paradigm encourages a one-to-one match between the emergency response plan incidents used by the operator, and the subsequent incidents used by the system developers in the system programming. This can have significant advantages for an integrated response between the operator and the system programmers because both parties are working to the same terminology.

In addition, NFPA publishes a standard that is pertinent to the role of the FMT. NFPA 3: Recommended Practice for Commissioning and Integrated Testing of Fire Protection and Life Safety Systems, outlines a systematic approach for the owner and the design team to provide documented confirmation that fire protection and life safety systems function as intended. The standard addresses the procedural concepts of fire-life safety system commissioning and also provides direction on the integrated system tests—tasks with which the FMT can assist.

Conclusion 

A well-integrated tunnel system will provide better functionality at all stages of a project including planning, implementation, commissioning, training, and operation. The FMT is a tool to assist with integrating the key stakeholders in the tunnel system design process including the operator, the designer, people who use the facility, the implementation staff, and emergency services. One of the greatest advantages of the approach is that it can be used to simplify the operator’s actions during an emergency, thereby improving the chances of a favorable outcome and greatly contributing to public safety.

As a leading consultant in fire-life safety engineering, WSP | Parsons Brinckerhoff is well placed to improve the delivery and perception of fire-life safety training and operation within tunnels for our clients. The FMT can help to achieve this and provide a safer road or rail facility.