CASE Studies

This case study outlines the comprehensive approach taken by a leading UK-based energy recycling company, in collaboration with our industrial hygiene consultancy services, to mitigate the risks associated with Chromium VI Cr(VI) during maintenance and refit operations of incinerators.

Chromium VI: Formation and Risks

Cr(VI) is an oxidized form of chromium, known for its high toxicity and carcinogenic properties. It is not naturally found in significant amounts in biological organisms or the environment but is primarily produced by industrial processes, including the incineration of wastes containing various forms of chromium. Cr(VI) forms during the high-temperature combustion of waste materials and can sometimes be observed as a yellowish deposit (Chromium Trioxide or Sodium Chromate) on surfaces throughout the latter stages of the incinerator. Simple instantaneous test kits can be used to confirm its presence. 

This formation process is influenced by several key factors:

• High-Temperature Conditions: The extreme temperatures necessary for waste combustion facilitate the oxidation of chromium compounds, converting them into the more toxic Cr(VI).

• Oxidation Processes: The presence of oxidising agents in the waste enhances the conversion of chromium to Cr(VI), especially under the oxidising conditions supported by the combustion air.

• Type of Waste Material: Specific types of waste, such as dyes, paints, inks, plastics, and other industrial wastes containing chromium, significantly influence Cr(VI) formation.

• Presence of Other Chemicals: Chemicals like chlorides and sulfates in the waste can react with chromium compounds under combustion conditions, promoting the formation of Cr(VI).

• Incomplete Combustion: If waste is not completely burned, incomplete combustion can lead to intermediate compounds that may further convert to Cr(VI).

The ERF incineration process involves a number of stages at which Chromium VI can be generated as follows, typically positive Chromium VI samples are detected in settlement dusts from the 2nd to 6th passes.

1st Pass: This is the initial section where the combustion of waste takes place. The flue gases generated here are at their highest temperature and contain the initial pollutants and residues from the combustion process.

2nd Pass: After the initial combustion, the flue gases move to the 2nd pass, where they begin to cool down. This pass often involves heat exchange processes to recover energy from the hot gases. Dust and residues can settle on surfaces in this pass, which may include materials like Inconel, a high-performance alloy resistant to high temperatures and corrosion.

3rd-6th Pass: These are subsequent stages where the flue gases continue to cool and additional energy recovery and cleaning processes occur. Each pass represents a further step in the cooling and treatment of the flue gases before they are released into the atmosphere. Dust and residues can also settle in these passes, and these stages are crucial for ensuring that pollutants are removed to meet environmental standards.

Chromium VI: Health Effects

The health risks associated with Cr(VI) are severe, including respiratory diseases, skin ulcers, and lung cancer when inhaled. Thus, workers and technicians involved in the operation, maintenance, and refit of incineration plants are at significant risk of exposure, especially during activities like welding, cutting, or when handling residues containing Cr(VI). Due to the sensitisation effect of Chromium VI and its carcinogenic nature exposures must be controlled and reduced not only to below the workplace exposure limit (WEL) but to as low as reasonably practicable (ALARP) under health and safety law.

Case Study: Energy Recycling Company’s Approach to Chromium VI

Our engagement with the energy recycling company involved a multi-faceted approach to managing Cr(VI) risks, focused on assessment, control, and continuous monitoring. Our monitoring services were pivotal in providing the client with detailed exposure control recommendations and identifying specific processes and work activities that generated elevated levels of Chromium VI.

Risk Assessment and Exposure Monitoring: We conducted a detailed risk assessment to identify potential sources of Cr(VI) exposure during the incinerator's maintenance. The robust monitoring program implemented included:

• Personal Breathing Zone Sampling: To capture airborne Cr(VI) particles inhaled by the workers.

• Environmental Monitoring: To measure Cr(VI) levels in the incinerator and surrounding areas.

• Biological Monitoring: Through urine analysis to detect Cr(VI) absorption in the body, ensuring that levels remain below the BMGVs of 10 µmol chromium/mol creatinine.

Regulatory and Compliance Framework

In response to the risk, strict regulatory standards have been set by the UK Health and Safety Executive (HSE). These standards define permissible exposure limits and mandate the implementation of safety measures to protect workers. The HSE specifies a legal exposure limit for Cr(VI) of 0.01 mg/m³ as an 8-hour time-weighted average (TWA) as described in EH40. Compliance with these regulations, particularly under the Control of Substances Hazardous to Health (COSHH) regulations, is crucial for ensuring the health and safety of employees. To put this level of exposure into context a full day's exposure to chromium VI at the legal limit of 0.01mg/m3 would equate to breathing in such a small quantity that it would only occupy 1/33rd of the space of a pinhead.

Biological Monitoring Guidance Values (BMGVs) and Monitoring

To complement the exposure limits, HSE has also established Biological Monitoring Guidance Values (BMGVs). For Chromium VI, the BMGV is set at 10 µmol chromium/mol creatinine in urine post shift. This value is instrumental in assessing whether the control measures in place effectively protect workers from excessive chromium exposure. BMGV monitoring involves collecting urine samples from workers at the end of their shifts to measure the levels of chromium compounds. This method provides an accurate indication of the amount of Cr(VI) that has been absorbed into the body, helping to assess whether safety measures are effectively preventing excessive exposure.

Implementation of Control Measures

A number of control measures were developed to reduce the overall risk of exposure to site operatives involved in the incinerator outage: 

• Elimination: Ferrous sulfate acts as a reducing agent that converts chromium VI to the much less harmful chromium III, the application of this solution sprayed onto surfaces helped reduce exposure levels.

• Engineering Controls: Use of Local Exhaust Ventilation (LEV) systems at critical points to capture dust particles at the source was an effect control. Additionally the incorporation of an air management system using airlocks and negative pressure units fitted with HEPA filters significantly reduced airborne levels inside the incinerator during refit activities and prevented spread of contamination at all entrance and exit points.

• RPE: As a last line of defence RPE (hooded positive pressure respirators fitted with P3 filters) were used to protect outage operatives. 

Our monitoring services provided the client with the assurance that they were effectively controlling exposure and meeting their legal requirements under COSHH regulations. The client was highly satisfied with the assistance provided for this specialist area of exposure monitoring, which ensured their operations remained safe and compliant.

Conclusion and Future Directions

Through the measures implemented, the company not only achieved compliance with health and safety regulations but also significantly enhanced the protection of workers from the dangers of Cr(VI). This case study serves as a model for similar facilities aiming to balance operational efficiency with stringent safety standards in the waste management industry.

For further advice call us on 0870 701970 or email: safetyexpert@euroenvironmental.co.uk