Bus Fire Suppression Systems

Michael Horgan Principal Consultant, Vehicle Services Bus Fire Suppression Systems

In addition to causing significant damage to valuable assets, fires on public transport systems present a significant risk to the safety of passengers. For various reasons there has been an increase in the incidence of fires on buses, resulting in an investigation by OTSI and the issue receiving attention in the media. The availability of effective, environmentally friendly engine bay fire suppression systems has enabled the risk to bus passengers to be significantly reduced. Transport for NSW has made the correct move in fitting these systems to the existing STA and Sydney Metro / Outer Metro bus fleets, says Michael Horgan, Principal Consultant – Vehicle Services at SNC-Lavalin Atkins’ business.

Bus Fires in NSW › And increasing loads on cooling systems (cooling fan drives etc.). In 2013 the Office of Transport Safety Investigations (OTSI) released a report entitled ‘An Investigation into • Tighter noise emission limits as a result of ADR 83, Bus Fires in NSW 2005 – 2012’. This investigation was has led to: initiated as a result of the number of fires occurring › Full engine encapsulation, hence the heat that during this period on buses and coaches which were is generated is more easily contained in the engaged in providing public passenger services. engine area It is difficult to accurately determine the number of bus › Engines have become less accessible and fires for a given period, though the number of insurance hence are harder to inspect and maintain. claims over time can provide a reasonable view of the trend. As provided by the Australian Insurance Industry, Additional causes could include: the number of insurance claims between 2007 and 2012 • The move to low floors, resulting in reduced air are shown in Figure 1. flow through engine bays. • More equipment being fit into the engine bay, such as additional exhaust emissions equipment, air conditioning compressors etc., which have also reduced airflow. The decision to install engine bay fire suppression systems. In 2015 the NSW State Government decided to fund, through Transport for NSW (TfNSW), the installation of engine bay fire suppression in both public and private operator buses. This program was commenced on the public State Transit Authority (STA) fleet. An incident involving an STA bus on the Sydney Figure 1: Bus fire insurance claims Harbour Bridge on 15 September 2016 (see Figure 2) (Source: Bus Industry Confederation, Submission to the brought bus fires to the attention of the wider public in Heavy Vehicle Safety and Productivity Program Round very spectacular fashion. Three, Sydney, September 2012)

An increase in bus fires The Bus Industry Confederation (BIC) Report ‘Fire Mitigation Advisory’ provided two main reasons for an increase in engine\ bay fires as follows: • Tighter Emission Standards, Euro 4, 5 and 6 which have typically resulted in: › Higher engine operating temperatures › Higher fuel injection and turbo charger pressures › Greater use of high temperature catalytic converters Figure 2: Bus fire on Sydney Harbour Bridge Sep 2016

Bus Fire Suppression Systems The bus had not been fitted with a fire suppression system The chemical reaction causes more heat, which at the time of the fire. It was due to be fitted about a month causes more vapours to be released form the fuel to following the incident. On date of the incident, 105 of the combine with the oxygen present, thus perpetuating 2164 buses in the STA fleet were waiting the installation of the fire. engine bay fire suppression systems. The remaining operational buses in the STA fleet were fitted with suppression systems shortly after the incident, in Extinguish or suppress? compliance with the planned program. Fire extinguishing or suppression involves removing one or more of the four elements from the Fire Private buses Tetrahedron. On 29 April 2016 TfNSW sought Proposals for the design, The systems fitted to buses are usually classified as supply, installation and related services for bus engine bay fire suppression systems rather than fire extinguishing fire suppression systems in Private Bus Operator (PBO) systems. This is because the main objective of the buses providing services in the Sydney Metro / Outer Metro system is not to provide a system that can be areas. All buses were fitted by August 2017. guaranteed to fully extinguish a fire in all foreseeable scenarios. While the engine bay fire suppression The Fire Triangle systems fitted to buses will extinguish a large portion of fires, the objective is to suppress the fire sufficiently Fire is often symbolised by a fire triangle (see Figure 3). The that passengers can be safely evacuated. three sides of the triangle are heat, oxygen and fuel. A fire requires all three of these elements for ignition and to be sustained. Types of fire suppression systems There are several types of fire suppression systems being used across various applications. The most common types can be categorised as follows: Water Mist: A water mist system acts by reducing the temperature while the water vapour mist expands providing a blanket over the fire, preventing oxygen from reacting with the fuel. Wet and Dry Chemical Agents: Chemical agents work to smother and extinguish fires, preventing oxygen from reacting with the fuel. Inert gases: Inert gases (e.g. nitrogen, argon) reduce Figure 3 – The Fire Triangle oxygen levels to a point where combustion cannot be sustained. They can act by smothering fires or by The Fire Tetrahedron reducing oxygen. While fire was symbolised by the Fire Triangle for many Carbon dioxide: Carbon dioxide suppression systems years, further research determined that a fourth element, a provide a heavy blanket of gas that reduce oxygen chemical chain reaction, was a necessary component of fire. levels to a point where combustion cannot occur. This Fire Tetrahedron model adds this extra element. This “fourth element” involves an exothermic chemical Bus fire suppression systems in NSW reaction that takes place between the fuel and oxygen, There are two types of engine bay fire suppression producing heat and light. A fire requires the chemical systems that have been fitted to the STA and Sydney reaction to occur for it to be sustained. A fire is initiated Metro / Outer Metro bus fleets. when heat causes the fuel to release vapours that will react The STA buses and most of the Sydney Metro / Outer with the oxygen to cause combustion. Metro buses were fitted with a Fogmaker water mist system, installed by Firestorm. A small number of Sydney Metro / Outer Metro buses were fitted with a Pyrogen dry chemical system, installed by Varley.

Fogmaker Fogmaker is a Swedish company that has been developing, manufacturing and marketing fire suppression systems for engine compartments with high pressure water mist since 1995. Today, they have more than 200,000 vehicles fitted with Fogmaker’s high-pressure water mist systems in more than 50 countries. Figure 4: The Fire Tetrahedron

Bus Fire Suppression Systems The Pyrogen system utilises an ABC dry powder. It is non-toxic and environment friendly. It is called ABC Dry Powder as it is used on A, B & C type fires. The ABC dry powder attacks the fire in a combination of two extinguishing actions: 1. chemical – by the removal of the fire propagating ‘chain carriers’; and 2. physical – by the removal of heat via heat absorption, evaporation and decomposition; dilution of the flame zone with a powder-gas cloud; and by the creation of a powder particles “fire blanket” on the Figure 3 – Fogmaker fire suppression system surface of the burning materials.

Fire Detection System The detector bottle is pressurised to 20-24 bar (2-2.4 Mpa). The detection tubing will rupture when the temperature reaches the design temperature of the detection system. When the tube ruptures the detection system depressurises. This loss of pressure in the detection tube triggers the release valve on the suppressant agent cylinder. Suppressant Delivery System Once triggered, the piston in the suppressant agent cylinder will operate and fill the delivery system with Figure 4 – Pyrogen fire suppression system the suppressant. The pressure in the delivery system will cause the protective caps on the nozzles to blow out. The suppressant is then delivered as an atomized Conclusion spray. Fire suppression systems greatly reduce the risk to The suppressant consists of water and an Aqueous public transport passengers. They also enable Film Forming Foam (AFFF) agent. The AFFF provides incidents to be brought under control more quickly, a thin aqueous film at the fuel/air interface that thus reducing the flow on impacts of such an incident. suppresses the combustion reaction. The damaged sustained by the assets is also reduced, providing benefits with reduced repair cost, a quicker return to active service and a reduction in the number Pyrogen of assets written off. Pyrogen Manufacturing was incorporated in 1999 and It is also acknowledged that the fire response has specialises in fire protection solutions. Pyrogen’s extended beyond suppression systems. Better thermal headquarters is in Kuala Lumpur, Malaysia. barriers, improved maintenance and driver training are some of the areas where improvements are producing Fire Detection System positive results. The Pyrogen system utilises a Linear Heat Detection (LHD) system for detecting the presence of a fire. The LHD cable is comprised of two conductors, individually coated with a heat-sensitive thermoplastic polymer that Michael Horgan is a Principal Consultant, Vehicle melts at fixed temperatures. Services at SNC-Lavalin’s Atkins business, now one of the world’s largest consultancies with more than 55,000 Once the polymer melts, the conductors initiate contact people employed globally of which 5,000 are specialist with one another, thus reducing the circuit resistance, rail consultants. We offer clients a complete end-to-end initiating alarms and activating the suppression system. range of services, unique breadth of capability, and a resource base that enables us to deliver all scales of Suppressant Delivery System rail projects globally. We combine traditional engineering with the latest techniques to deliver safe, Once the LHD cable senses a high temperature, the reliable and sustainable outcomes, transforming rail pressure generator triggers, discharging the networks and shaping the future of transport. suppressant powder.

Bus Fire Suppression Systems