Maximum Safe Egress Distance in Conveyor Tunnels
There are many factors which affect the ability of occupants within a service tunnel to escape safely during a fire event and there are as many opinions of what the maximum safe egress distance within these tunnels should be and which design criteria should apply.
The required safe egress distances are well defined in standards, codes and legislation for residential and commercial buildings, public infrastructure and road and rail tunnels; however, there are no specific requirements outlined for industrial service tunnels such as coal conveyor tunnels within port facilities. The purpose of this study is to explore some of the issues associated with determining the design requirements for egress distances within coal conveyor tunnels, and present the International Fire Engineering Guidelines as a framework for specifically evaluating the occupant life safety through a semi-quantitative risk assessment.
The methodology used in this study was to review the legislation, standards, codes and guidelines that are often used during the design of coal reclaim tunnels and determine their relevance. The relevant stakeholders were then consulted to determine any specific requirements for the design of the reclaim tunnels. Once this was completed, the trial fire and egress design was determined during a stakeholder workshop and the International Fire Engineering Guidelines were used as a framework to assess this design against recognised and accepted criteria.The Wiggins Island Coal Export Terminal project was used as a case study for this analysis. The study identified the following regarding egress distances within coal reclaim tunnels:
- There is no legislation, codes, standards or industry guidelines that specifically state the requirements for maximum egress length for service tunnels, such as coal reclaim tunnels, in Australia;
- Often the guidelines used are based on road or rail tunnels and are not appropriate and shouldn't be applied in these situations;
- In the case study presented and in the situations that were identified and simulated, an able bodied occupant could “out walk” the descending smoke layer and egress safely regardless of the length of the coal reclaim tunnel; and
- Any tunnel within Queensland that requires the attending fire brigade, utilising standard single cylinder self-contained breathing apparatuses, to travel longer than 100m out of a safe zone, is too long to perform firefighting or rescue operations in compliance with their Standard Operating Procedures safety protocols.
Regardless of how the initial criteria are determined, it should then be backed up with a semi-quantitative or quantitative risk assessment. The framework presented in the IFEG‟s was used in this case study and found to be robust and suitable for specifically evaluating the occupant life safety through a semi-quantitative risk assessment.