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Friday , 30 September 2022

Reducing the risk of bus fires

Björn-SundströmSP Fire Research, Sweden is one of the largest  fire research facilities in the world and has  been active in promoting bus fire safety for  more than a decade. Björn Sundström, Head, and Fredrik Rosen, Marketing Manager SP Fire Research, outline how bus fire safety research can reduce the risk of fires

Aircraft, trains and passenger ships all have well established standards, regulations and certification processes to ensure the maintenance of high levels of fire safety as new materials and constructions are introduced. Buses, however, mostly rely on the efforts of the original equipment manufacturer (OEM), operators and suppliers of fire systems to ensure safety with few strict regulations.

Fredrik-RosenBus fire safety encompasses many aspects of design, operation, maintenance, evacuation and even first responders. Each has a critical role in establishing effective standards and best practices but are typically the responsibility of different stakeholders in the development process. Buses pose many unique challenges in regards to fire risks. The varying modes of operation (city, highway and long distance), unique vehicle types (school, transit and coach) and design changes to meet new emissions standards provide the context for fire safety. Every fire hazard, whether it is an engine compartment, battery compartment, wheel well or even a luggage compartment, poses unique challenges in the way of geometry, airflow, clutter, flame spread and evacuation.

The engine compartment is a wellknown fire hazard that provides particular challenges for detection and suppression of fires. Ventilation, through fans and openings, is necessary for cooling but will also increase fire intensity and fire spread. The particularity of a windy and often dusty environment in the engine compartment influences the potential for fire detection and fire suppression.

New international standard/ certification for bus engine fire suppression

SP Fire Research has established a certification process (SPCR183) and test method (SP Method 4912) for testing fire suppression systems against known fire threats and environmental conditions specific to bus engine environments. A major part of the test method was adopted in UN ECE Regulation 107 in November 2015. The regulation states that, as of June 2018 for new types of vehicles and June 2019 for all existing types, installation and testing of fire suppression systems will be mandatory in engine compartments of all single-deck, double-deck, rigid or articulated vehicles of category M2 or M3; and specifically in vehicles with a capacity exceeding 22 passengers, ‘Class III’ vehicles. These installations will follow transitional provisions and are indeed a major step towards increased fire safety in buses.

In the SP P-mark system, the suppression systems are fire tested but the incorporated components are also tested for mechanical and thermal stress resistance, corrosion resistance and ingress protection rating of electrical equipment. In addition, a risk assessment has to be made prior to installation of the system by an experienced professional. Further, an annual follow-up inspection of the manufacturer’s production facility and quality control plan ensures compliance with the requirements of the certification rules. Successful systems are then issued a certificate and allowed to ‘P-mark’ their components.

Preventive fire safety

Bus fires that occur often relate to component failures. Due to this, SP is developing a new certification system: SPCR 190 – Certification rules for vehicle manufacturers, operators and authorised service centres (workshops) with regard to fire safety. The P-certification will enable the manufacturer/body builder/operator/ authorised service centre (workshop) to certify their fire risk mitigation process. The P-certification will ensure that personnel, strategies and techniques involved in fire safety mitigation of new and existing vehicles are kept at the highest performance level, that new information in this area is incorporated and updated into best practice working procedures, ensuring that the customer will operate at the front line of vehicle fire safety engineering. The certification consists of three different labelling systems: P-vehicle manufacturer, P-operator and P-workshop.

The certification is composed of the following elements: 1) Risk assessment; 2) Quality procedures and configuration management (document control); 3) Safety certification training programme; 4) Reporting of thermal events – database; 5) Initial assessment of the manufacturer’s factory production control (FPC); and 6) Annual audits of the FPC and follow-up risk assessments on selected bus model. Three of these elements are explained in more detail below.

Future goals

Fire safety in buses has been the focus of significant research in recent years but much improvement remains, particularly in relation to fire prevention and safe egress. The sharing of information and best practices can benefit all parties but, most importantly, passenger safety. SP has identified particular areas for necessary fire safety research, listed below. Some research has already been funded and is in progress; for others, we are actively searching for funding opportunities.

Wheel well fires

The exposed environment and deep seated fire risk makes wheel well fires particularly difficult to detect and suppress. Tests have shown that it can take less than five minutes before toxic fumes and smoke enter the passenger compartment. Tyre pressure/temperature monitoring systems represent one method for early detection; other methods need to be explored. Early testing of some coatings in the wheel well area have been shown to provide a significant increase in the evacuation time before toxic fumes enter the passenger compartment. Continued work in this area could provide a low cost solution.

The manufacturers, operators and authorised service centres must complete regular fire risk assessments and a system hazard analysis (SHA), which is a systematic study to identify hazards and make recommendations for their elimination or control during all phases of the lifecycle of the system

Bulkheads/fire partitions

The bulkheads between high risk areas such as the engine compartment and the passenger compartment can allow toxic fumes and flames to spread into the passenger compartment. New materials and the increased complexity of systems connecting the engine compartment to the driver area might increase fire hazards.

Detection systems

SP is currently working on a project to develop a new test method and propose a standard for fire detection and fire alarm systems in heavy vehicles.

Use of flammable material in high risk areas

The need for lighter, less costly materials in high risk areas is always present; but there are few standards and regulations regarding the flammability and toxic fume production of such material. Further research is necessary to establish adequate performance requirements for the use of flammable material in high risk areas in buses and coaches.

Electrical fires

Electrical fires are not something new but are increasing in hybrids and electrical vehicles. Electrical arcs and short circuits do not always trip protective devices, e.g. fuses, and some cables carry high currents capable of producing enough heat not only to ignite nearby combustible materials, but also to cause breaches in hydraulic lines and metal covers.  The adoption of best practices for  routing, securing and protection can greatly reduce the risks. Early detection methods such as current monitoring or better circuit protection should be explored.

Alternative fuels

All over the world, new alternative fuels are emerging to replace fossil fuels. Hybrids, natural gas, all electric and even hydrogen buses are currently being used. The overall benefit is great but with new fuels and new technical solutions, the fire hazards also change. In addition, first responders face new risks. New fuels, e.g. ethanol, enforce new types of extinguishing strategies. The image shows the scenario after an ethanol fire has been extinguished using an alcohol resistant foam. Some countries have been using alternative fuels for more than 20 years, others are just beginning. A major hindrance to the introduction of such fuels is the perception of an increased fire risk. Dissemination of present knowledge and development of new data is key to the wide scale introduction of alternative fuels.

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