RISK ASSESSMENT
The carbon dioxide quantity could be 50kg or 1 million tons. It is only logical that special provision (added safety measures) must be included for occupied spaces. Current guidelines list machinery rooms as being unoccupied spaces without general access. Best practice here is to ensure the areas are airtight from other spaces. These types of locations should only be accessed by trained employees and must have gas detection and ventilation systems with extractor fans that increase emergency air flow if the carbon dioxide concentration exceeds safe limits. According to EN378, open air locations are
“rooms where at least one of the longer walls is open to the outside air by means of louvres with 75% free area and covering at least 80% of the wall area”. Even though these areas are open to outside air, they may still require gas detection and ventilation systems – and it’s crucial to check to ensure carbon dioxide isn’t stagnating. EN378 requires unoccupied spaces to meet the same requirements as machinery rooms with 4 air charges per hour for occupancy ventilation and also the calculated emergency ventilation requirment. However where extract hood are installed above non permanent joints the ventilation can be greatly reduced. Extract hoods must be designed to account for the possible of a carbon dioxide releases when a technician is working on equipment inside the hood. Wherever carbon dioxide relief valves are
present, there’s a risk solid material can block valve vent lines. To overcome this, the valve outlet pipework arrangement should be kept simple with no branches, tees, or other areas where this material could deposit following a discharge. It’s vital to assess this hazard, as a release of solid carbon dioxide horizontally can act like a lethal bullet, exiting at high velocities of >200m/s. Assessors should also make sure that any discharged carbon dioxide is not sucked back into buildings through ventilation systems, as this can result in dangerously high atmospheric amounts. As carbon dioxide falls under the DSEAR
regulations, management must take steps to ensure an effective emergency response plan is in place to deal with related accidents and leaks. The plan should be tested to assess its workability and efficiency, preferably when all personnel are on site.
Whilst the owner/user is responsible for compliance to DSEAR, EN378-2 requires the installer to provide information for safe operation of the refrigeration system and outline the emergency procedures for the site to use in the event of a carbon dioxide release. The regulation also requires arrangements to deal with accidents,
incidents and emergencies. Although the facility’s management are ultimately responsible for any failures, they are also required to manage their contractors working on site to HSE guidance HGS 159. When using a Permit To Work (PTW) system, those managing contractors must be competent to work to the HSE guidance HGS 250. There is a further requirement to provide employees with information, instruction and training. A suitable and sufficient carbon dioxide release
response plan should include emergency phone numbers, along with a location map detailing where carbon dioxide systems are present and where personnel should go in the case of a gas alarm or emergency if a leak or incident occurs, so that harms can be minimised quickly. If personal detectors are issued to staff, they should be regularly checked as part of the testing process, while managers should know how to spot signs of carbon dioxide inhalation, as well as when to evacuate or contact emergency services. Presenting response planning procedures in an easy-to-follow flow chart formula will allow staff to act swiftly in the case of an emergency –but any type of plan should cover all areas where carbon dioxide is present and could reach toxic levels. Employee training Employees, contractors and anyone working at locations with carbon dioxide systems must undergo an induction when they start at site. This should provide details of carbon dioxide refrigeration systems are located and how to spot signs of a release.
Staff should let management know in the event of an emergency before congregating at the assigned meeting point if they have concerns. They must be able to recognise the sound of installed alarms and know what to do when one is initiated. If a lot of carbon dioxide is stored onsite, managers and anyone who’ll be entering high risk areas, such as machinery rooms, should complete a carbon dioxide safety course. Approaching risk assessment of carbon dioxide
refrigeration systems and emergency response planning systematically is the best way to ensure major risks are identified and minimised. Although current legislation doesn’t go quite as far as to lay out full working practice, the European standards provide sufficient guidance for owners and operators to plan a measured response. The goal of any carbon dioxide risk assessment is to establish the risk rating (frequency x severity). Where the risk rating is found to be too high, it should be reduced by appropriate actions. A standard format for carbon dioxide hazard assessments is a combination of a hazard study and risk assessment. The document should be split into four sections:
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Q Introduction, Actions and Compliance to Regula- tions
Q Carbon Dioxide Regulations, Standards and Good Practice
Q Compliance to Regulations and Good Practice Q Risk Assessment.
Section 1 should introduce the document and then detail the immediate actions required where the risk rating is considered too high under the headings: Pressure System Integrity Inspections, Site Management Systems, Safe Maintenance and Repair and Safety Hardware Compliance. There are further requirements related to the frequency of the actions that must be carried out to ensure the refrigeration systems remain safe. Section 2 should identify the limitation of the risk assessment, characteristics of carbon dioxide with COSHH and toxic effects. The section should then go into further detail to scrutinise the requirement for: the avoidance of the release of hazardous substances, ventilation, gas detection system, the safe release of carbon dioxide, carbon dioxide release response plans and on-site personnel awareness.
Section 3 should detail the purpose and location of all carbon dioxide equipment, the gas detection system with auxiliaries, ventilation system safety systems, and state where carbon dioxide is vented directly or indirectly. There must be a list of compliance questions to assess system safety and compliance with the requirement set in section 2. If the requirement is not met, an action should be labelled and detailed in section 1.
Section 4 should include a carbon dioxide risk assessment and establish the risk rating for the present and future control measures.
Future proof cooling Refrigeration systems charged with carbon dioxide offer a climate friendly, long term alternative to HFCs for numerous applications. Well designed, maintained and risk-assessed carbon dioxide systems are a safe, reliable and a highly efficient solution. While regulations do not detail safe work
practices for refrigeration systems, European standards provide guidance on safety requirements for the design and operation of carbon dioxide refrigeration systems which must be followed to comply with UK legislation. The systematic approach to assessing carbon
dioxide refrigeration systems described in this article will ensure the safe operation of the equipment, minimise carbon dioxide leaks and institute a suitable plan to address any potential gas release.
www.acr-news.com • November 2022 13
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