Gross Pollutant Trap Cleaning Safe Work Method Statement

GPT chambers can contain multiple atmospheric hazards from decomposition of organic matter and sewage contamination. Primary hazards include: Hydrogen sulphide (H2S) - extremely toxic gas with rotten egg smell at low concentrations but smell disappears at high concentrations creating false sense of safety. Safe exposure limit is 10 ppm time-weighted average over 8 hours. Concentrations above 10 ppm cause immediate eye and respiratory irritation, above 50 ppm cause serious health effects, above 100 ppm cause rapid unconsciousness, and above 500 ppm cause immediate death from respiratory paralysis. H2S is heavier than air accumulating in chamber bottom in breathing zone. Methane - flammable gas from anaerobic decomposition creating explosion risk at concentrations 5-15% (explosive range). Lower explosive limit (LEL) is 5% - atmospheres above 5% LEL are immediately dangerous requiring evacuation and ventilation. Methane is lighter than air but can accumulate in poorly ventilated confined spaces. Oxygen deficiency - bacterial consumption of oxygen and displacement by heavier gases can reduce oxygen below 19.5% minimum required for human respiration. Atmospheres below 19.5% oxygen cause asphyxiation with unconsciousness occurring within minutes and death following rapidly. Carbon monoxide - toxic gas from incomplete combustion or decomposition, safe limit 30 ppm time-weighted average. These gases cannot be detected by human senses reliably - odors may be absent particularly at dangerous concentrations. Only way to assess atmosphere safety is using calibrated electronic gas monitor measuring oxygen, hydrogen sulphide, methane/combustible gases, and carbon monoxide before and during any chamber access. If readings exceed safe limits, entry prohibited until mechanical ventilation provided restoring safe atmosphere verified by re-testing.

Confined space entry permit is required under WHS regulations when GPT chamber meets confined space criteria: substantially enclosed, not designed for continuous human occupancy, has restricted entry or exit, and may present atmospheric hazards or engulfment risks. Most GPT chambers exceeding 1.5 metres depth qualify as confined spaces. Chambers shallower than 1.5m may also be confined spaces if restricted access (small manhole openings) or known atmospheric hazards present. Entry permit documents: atmospheric testing results before entry showing oxygen 19.5-23.5%, H2S <10ppm, methane <5% LEL, CO <30ppm, authorized entrants and standby person names and competencies, ventilation provided and verified effective, retrieval equipment positioned and tested, emergency contacts including nearest hospital and rescue service, validity period (permits typically valid for single shift only), and supervisor authorization confirming all controls implemented. Mandatory controls for confined space entry include: Atmospheric testing before entry using calibrated 4-gas monitor, continuous monitoring during entry using personal gas detectors with audible alarms, mechanical ventilation providing fresh air throughout entry (minimum 6 air changes per hour), trained standby person remaining at entry point throughout entry period never entering chamber to perform rescue, emergency retrieval equipment (tripod, winch, full-body harness) allowing rescue without rescuers entering space, established communication between entrant and standby with regular check-ins (every 5 minutes minimum), personal protective equipment appropriate for hazards (chemical resistant clothing if contamination present, respiratory protection if airborne hazards), and rescue procedures including calling emergency services immediately if incident occurs rather than attempting unprotected rescue. Alternative approaches should be considered before entry including vacuum truck cleaning from surface, extended-reach tools, or remote camera inspection eliminating entry requirement. Entry should be last resort when no surface cleaning method feasible. Penalties for non-compliance with confined space regulations are severe particularly if incidents occur - multiple fatalities have resulted from entry without proper controls when rescuers enter attempting to save collapsed workers without proper equipment.

GPT cleaning exposes workers to multiple infectious disease risks from contact with contaminated water, sewage, organic matter, and discarded waste. Primary infectious risks include: Gastroenteritis from various bacterial and viral pathogens including Salmonella, E. coli, Campylobacter, and norovirus causing severe diarrhea, vomiting, and dehydration requiring hospitalization in serious cases. Hepatitis A viral infection affecting liver transmitted through fecal-oral route from sewage contamination, causing jaundice, fatigue, and potential long-term liver damage. Leptospirosis (Weil's disease) bacterial infection from rat urine contaminating surfaces in drainage systems, entering through cuts or mucous membranes causing kidney and liver damage potentially fatal if untreated. Tetanus from soil contamination entering through wounds caused by sharp materials or puncture injuries, causing severe muscle spasms and potential respiratory failure. Blood-borne infections including hepatitis B, hepatitis C, and HIV from needle-stick injuries from discarded syringes, transmitted through blood contact requiring immediate medical assessment. Recommended vaccinations for workers regularly exposed to sewage or contaminated drainage include: Hepatitis A vaccine - 2-dose or 3-dose series providing long-term protection, essential for workers with regular sewage exposure. Tetanus-diphtheria booster - required every 10 years with updated booster if wound contamination occurs more than 5 years after last dose. Hepatitis B vaccine - 3-dose series providing protection against blood-borne hepatitis, recommended for workers at risk of needle-stick injuries. Additional protections beyond vaccination include: proper PPE use with impermeable gloves, face shields, and protective clothing preventing contamination contact, no-touch protocols prohibiting contaminated gloves touching face or eating/drinking before hand washing, thorough decontamination after work washing hands with soap and water for minimum 20 seconds, immediate first aid for contamination exposure irrigating eyes or wounds with clean water and seeking medical assessment, and reporting all needle-stick injuries immediately for post-exposure prophylaxis consideration. Workers should be educated on symptoms of infectious diseases seeking medical attention if developing fever, jaundice, severe diarrhea, or flu-like illness after contamination exposure mentioning occupational exposure to healthcare provider for appropriate testing and treatment.

Material removed from GPT chambers requires proper classification, handling, and disposal complying with environmental protection and waste management regulations. Waste classification depends on contamination type and level. Typical GPT waste contains litter, organic debris, sediment, and stormwater runoff pollutants classified as general solid waste suitable for landfill disposal. However, waste may be contaminated requiring special handling: if sewage contamination present (from illegal connections or cross-contamination), material may require disposal at facilities licensed for putrescible or contaminated waste, if industrial pollutants present (heavy metals, hydrocarbons, chemicals), laboratory testing may be required to determine hazard classification and appropriate disposal, if sharps present (syringes, broken glass), material requires disposal as contaminated/clinical waste at appropriate facility, and if asbestos-containing materials found (old pipe lagging, building materials), asbestos protocols including testing, licensed removal, and disposal at approved facility required. Waste handling and transport requirements include: containerization in sealed bags or bins preventing spillage and odor during transport, labeling indicating origin and basic contamination information for disposal facility, transport in covered vehicles preventing environmental release, manifesting for tracking particularly if contaminated waste requiring documentation, and disposal at facilities licensed for waste type being transported. Environmental considerations: GPT cleaning generates large volumes of contaminated water particularly when using jetting or washing methods - this water cannot be discharged to stormwater requiring collection and disposal to sewer (with authority approval) or transport to wastewater treatment facility, sediment and organic material should not be disposed into waterways despite originating from drainage system as concentrated loads create environmental harm, and vegetation or green waste suitable for composting if uncontaminated but should not be composted if sewage or chemical contamination suspected. Record keeping: document material volumes removed for asset management records, maintain waste disposal receipts demonstrating proper disposal, and track disposal locations for compliance auditing. Cost management: proper waste classification and disposal is cost of GPT maintenance - attempting to avoid disposal costs through illegal dumping creates environmental harm, prosecution risk, and significant penalties. Budget adequately for proper waste disposal as essential component of GPT maintenance program. If uncertain about waste classification, obtain professional advice from environmental consultant or waste disposal specialist preventing inappropriate disposal creating liability.

GPT cleaning during wet weather or flooding conditions presents additional hazards requiring careful assessment and modified procedures or work postponement. Atmospheric hazards increase during wet weather as fresh runoff washes organic material into chambers accelerating decomposition and gas production - hydrogen sulphide and methane levels can spike rapidly during wet periods requiring more frequent atmospheric testing and continuous monitoring. Flooding conditions can fill chambers completely with water creating drowning hazards if entry attempted - chambers should not be entered during flooding regardless of other precautions. Rising water during entry creates evacuation emergency - monitor weather and cease entry if rain developing. Confined space hazards amplify as water filling chamber reduces air space and increases buoyancy of entrant creating retrieval difficulty. Visibility reduces during wet weather affecting traffic management effectiveness and increasing struck-by risks - consider postponing roadway GPT cleaning until weather clears and visibility improves. Contamination levels increase as combined sewer overflows or illegal sewage connections discharge during heavy rain increasing pathogenic exposure - enhanced PPE and decontamination more critical during wet periods. Equipment operation becomes more difficult as wet conditions make grates slippery and increase manual handling risks - mechanical lifting becomes mandatory as wet grates cannot be safely hand-carried. Work procedures during wet weather include: comprehensive atmospheric testing with extra caution as readings can change rapidly during rainfall, enhanced ventilation with increased flow rates and continuous operation maintaining safe atmosphere despite ongoing contamination source, modified traffic management with additional warning devices accounting for reduced visibility, postponement of chamber entry if any uncertainty about safety waiting for dry weather allowing safer access, vacuum truck operation from surface exclusively during wet weather eliminating entry requirement, and increased monitoring frequency testing atmosphere every 5 minutes during entry rather than pre-entry only. Decision to postpone: GPT cleaning should be postponed if moderate to heavy rain predicted during work period, if chambers already flooded preventing safe access, if weather conditions make traffic management unsafe (visibility below 100 metres), or if lightning present creating electrocution risk for workers operating electrical equipment near water. GPT functionality paradox: GPTs require cleaning most urgently during wet weather when they're actively treating stormwater but wet weather also creates most hazardous cleaning conditions. Optimal approach is regular cleaning during dry weather preventing chamber filling and maintaining capacity for next wet weather event rather than attempting emergency cleaning during storms.