Evacuation & Rescue from a Deep Tank

Jonthan Piggot, BE (Enviro), CPEngNZ, Watercare Services Limited, NZ

During a review of maintenance cost for overhauling a reactor clarifier (RC) at the Māngere Wastewater Treatment Plant (WWTP), it was identified that several different methods of egress were recorded as rescue plans from a confined space (a tank 6+ meters deep) by different internal and external parties. The cost of these alternate methods also varied from a few thousand dollars to tens of thousands of dollars. 

A series of workshops were held to better understand why there was such a difference in method and cost. Professionals within the rescue and first aid space were invited to participate in these workshops. 

Outcomes of the workshops revealed that different groups placed greater weighting on their own approach to ensuring a rescue plan was in place. Some had used minimum cost solutions to provide cost-effective pricing such as davit arms with winches or narrow scaffold towers with ladders, while others selected costly options such as a crane with a man cage on standby. Nobody had trialled the evacuation option they had selected, and all assumed that their preference would work.

Some rescue plans considered it the emergency services role to rescue anyone that was severely injured or who had suffered a medical event. Fire and Emergency New Zealand (FENZ) and St Johns both said they would always attend site and help, but ultimately, the company had a duty to ensure a rescue plan was in place. Looking more closely at some of the noted rescue plans, it seemed that some would be considered a technical lift (lifting greater than 6m) and would be more appropriate for FENZ to perform. However, this approach was challenged with the counter that the rescue plan was probably not appropriate if set up for someone else to perform the rescue.

After considering several options, a scaffold tower with 4 flights of 1.4m wide stairs was constructed inside both the reactor and clarifier zone of the RC. Over several weeks multiple exercises were run with a mixture of WWTP staff, contractors, FENZ and St Johns to trial the option. The exercise involved rescuing an 80kg dummy in a stretcher up the stairway structure.

Many lessons were learnt, and constructive and informative feedback received from all involved. Having staff involved throughout all the workshops and exercises in this H&S matter provided hugely positive outcomes. The endorsement of FENZ and St Johns in the proposed rescue solution and the familiarisation they gained of the facility was priceless. Consideration for design of access hatches in future infrastructure projects was noted as required in safety and design and setting a minimum standard for egress for a rescue plan another worthwhile outcome.