Case Study: Hazardous Area Classification and Risk Assessment for Wastewater Treatment

The Client
A wastewater treatment facility implementing a new thermal drying system for sewage sludge. The client needed to ensure that their proposed system complied with all hazardous area regulations and minimised the risks of fire or explosion 

The Goal
The client required a thorough hazardous area classification and combustible dust risk assessment for the thermal drying system.  Sewage sludge is prone to catching fire as it dries and there have bene sludge fires at Wastewater treatment plants.  The goal was to ensure that the equipment design met regulatory compliance requirements and that all potential fire and explosion risks were minimised as much as possible during the design phase.

Why TEG Risk Was Chosen
TEG Risk was selected for their in-depth expertise in hazardous substances and combustible dust risk assessments. Our proven ability to provide detailed, practical recommendations and clear, compliant designs made them the ideal partner for this critical project. The client valued TEG Risk’s comprehensive approach, from classification to risk mitigation strategies.

Solution:

TEG Risk’s seasoned team of engineers and risk management experts applied their extensive experience in hazardous area classification and combustible dust risk assessment to deliver a tailored solution for the proposed thermal drying system. The team mapped out the entire operational workflow, identifying zones that posed the highest risk of fire or explosion due to combustible dust. Leveraging their experience working with complex industrial systems, the TEG Risk team was able to the fire and explosion risks unique to this project.

To ensure compliance with the AS/NZS 60079 series (which governs explosive atmospheres), TEG Risk prepared a detailed report and sources of release table from which was generated accurate, formalised hazardous area drawings. These detailed drawings were critical for guiding the design team in selecting the right electrical equipment for installation in high-risk areas but also identifying the zones where combustible dust and ignition source risk assessments were neexed. The zones were classified into different levels of hazardous risk (such as Zone 20, Zone 21, and Zone 22) based on the frequency and duration of the presence of combustible dust, ensuring that only equipment certified for those environments would be used.

In addition to hazardous area classification, TEG Risk conducted a comprehensive combustible dust risk assessment aligned to AS/NZS 4745 Code of Practice, which allowed for the systematic identification of both electrical and non-electrical ignition sources. Tools were used to model potential fire and explosion consequences e.g. fireball size and area personnel occupancy, these provided information as to the consequences of such incidents.  Based on the detailed knowledge of combustible dust risks and the acquired knowledge of the process and plant TEG Risk could determine the likelihood of these explosions, enabling the team to assign accurate risk levels for each hazard identified.

The actionable recommendations provided for the client were practical and based on quantitative findings. They included:

  • Ventilation Improvements: Installing enhanced ventilation systems in high-risk zones to reduce the accumulation of potentially explosive gases and dust.
  • Explosion-Proof Equipment: Specifying the installation of explosion-proof motors, lights, and other electrical components in accordance with the hazard classification of each zone.
  • Regular Equipment Inspections: Developing a schedule for routine inspections and maintenance of electrical equipment, focusing on early detection of wear or failure that could introduce ignition risks.
  • Ignition Source Controls: Recommending strict control measures around static electricity, including grounding and bonding of all conductive materials to prevent static discharge in sensitive zones.
  • Emergency Shutdown Systems: Implementing automated emergency shutdown systems that isolate power and stop the drying process in case of detected hazards, reducing the likelihood of escalation during an incident.

These recommendations were designed to comply not only with New Zealand’s Health and Safety at Work Act (HSWA) 2015 and the General Workplace Regulations 2016. The proposed safety measures ensured that the client’s operations would meet all required regulatory standards, minimise the risk of non-compliance, most importantly, safeguard the health and safety of their workforce and integrity of their plant

By applying the expertise of its risk management team and using the latest tools and techniques for hazard identification, TEG Risk provided a robust solution that not only met the legal compliance requirements but also delivered long-term safety and operational reliability for the thermal drying system.

Challenges
The main challenge was the complexity of working with sewage sludge, a material with unique explosive properties. Working with sewage sludge presents various complexities, including its variable composition, which affects behaviour during treatment, and the combustible nature of dried sludge, posing fire and explosion risks. Additionally, regulatory compliance is stringent, with odour control, moisture management, and high energy consumption add further challenges to system design and operation all of which needs to be considered in the risk assessment so Efficient handling and storage are also crucial to prevent fire and explosion.  Any down time in plant due to a fire caused by inadequately controlled risks could also have a downstream impact on environmental compliance associated with sludge disposal.

Therefore the design stage required precise recommendations to ensure that risk mitigation was built into the system from the outset. TEG Risk ensured that the client was fully compliant with relevant New Zealand and Australian safety regulations and international standards governing hazardous areas. Specifically, the AS/NZS 60079 series and AS/NZS 4745 for explosive atmospheres was a key standard applied. This set of regulations defines the classification of hazardous areas, the proper installation of electrical equipment in such zones, and risk management measures to mitigate potential ignition sources. Additionally, the client was guided to adhere to WorkSafe New Zealand’s regulations on hazardous substances and workplace safety, including the Health and Safety at Work Act (HSWA) 2015.Balancing compliance with AS/NZS regulations while minimising the risks of fire or explosion was a critical factor in the project’s success.

Results
TEG Risk provided the client with a clear, actionable hazardous area classification and risk assessment, ensuring the thermal drying system met all compliance requirements. The deliverables included zone classification drawings and a comprehensive set of recommendations that significantly reduced the risk of fire or explosion. As a result, the client was able to proceed with confidence, knowing that their system design was safe, compliant with the AS/NZS 60079 series and AS/NZS 4745 for explosive atmospheres, and operationally sound.

Do you have a Hazardous Substances or Combustible Dust challenge that requires expert guidance? Get in touch with our experienced team today.