Shotcrete Safety in Dubai: Managing Chemical Hazards in Underground Works

Sprayed concrete, or shotcrete, remains a fundamental engineering process across Dubai's civil construction sector, underpinning deep basement retention piling, shaft sinking, and subterranean infrastructure projects overseen by Dubai Municipality and the Roads and Transport Authority (RTA). Globally, underground engineering standards are driving a technological transition toward alkali-free liquid accelerators over traditional caustic aluminate and silicate chemistries. For UAE main contractors operating in deep excavations, diaphragm wall construction, and utility microtunnelling, this transition is not merely a material science upgrade; it represents an essential engineering and occupational health control that directly impacts ground crews and plant operatives.

Dubai Regulatory Context and Underground Chemical Exposures

Deep subterranean excavations in Dubai present unique occupational hygiene challenges, where confined working areas, ambient heat, and limited natural airflow compound the hazards of airborne chemicals and fine particulates. Under the Dubai Municipality Code of Construction Safety Practice and applicable health and safety guidelines in free zone jurisdictions (such as Trakhees within PCFC areas), main contractors are required to implement effective control measures for hazardous substances, adequate subterranean ventilation, and collective protective equipment. Traditional shotcrete accelerators contain aggressive alkaline compounds with a pH frequently exceeding 12, presenting catastrophic risks of irreversible chemical burns, skin ulceration, and permanent eye trauma to nozzlemen and support crews in the event of hose failures or rebound. Modern alkali-free accelerators, which typically maintain a mildly acidic pH between 2.5 and 4.0, significantly reduce the severity of acute caustic burns, but they still introduce acidic mist inhalation hazards that require robust risk assessments and precise handling procedures.

Common Pitfalls on UAE Excavation and Shoring Sites

Despite technical submittals identifying high-risk excavation activities, site inspections and safety audits frequently uncover critical breakdowns in procedural discipline during concrete spraying operations:

• Treating accelerator admixtures as benign concrete chemicals without reviewing the manufacturer Safety Data Sheet (SDS) for specific incompatibility risks and emergency exposure measures.
• Relying on standard disposable particulate masks rather than full-face respiratory protection or powered air-purifying respirators (PAPR) inside deep shafts where aerosolised admixtures and respirable crystalline silica (RCS) concentrate.
• Over-dosing accelerators at the nozzle to counter high concrete temperatures during warmer months, leading to excessive rebound rates, erratic setting times, and dense clouds of airborne chemical mist.
• Placing portable eye-wash stations too far from the active nozzle zone or allowing wash water reservoirs to overheat in direct sunlight, rendering emergency decontamination dangerous or inaccessible.
• Failing to establish physical exclusion zones around the active rebound perimeter, allowing secondary trades such as steel fixers or waterproofing teams into the line of fire.

Site Checklist for Sprayed Concrete Operations

• Chemical Verification: Confirm that the delivered accelerator matches the approved technical submittal and Chemical Risk Assessment, verifying whether alkali-free formulations are in use and that corresponding SDS sheets are displayed at the batching unit.
• Mechanical Ventilation: Verify that auxiliary forced ventilation is operational in shafts and basement corners prior to spraying, maintaining effective air movement that directs chemical mists away from nozzle operators.
• Operative PPE Ensemble: Mandate chemical-splash goggles combined with full face shields, impermeable overalls, heavy-duty chemical nitrile gloves, and appropriate respiratory protection fitted with combined particulate and mist filters.
• Exclusion Boundaries: Erect physical barriers and high-visibility warning signs delineating the active spraying zone, strictly restricting entry to competent, trained nozzlemen and designated pump assistants.
• Emergency Decontamination: Inspect and test self-contained eye-wash units and drench stations at the start of every shift, ensuring immediate access within close reach of the spraying face with clean, temperature-controlled water.

Digital HSE Governance on Active Excavation Projects

Translating material substitutions and chemical safety protocols into consistent daily habits across deep excavation works requires real-time supervisory tracking. Digital safety platforms enable HSE managers to link daily spraying permits directly to approved chemical risk assessments, log georeferenced photos of ventilation ducts and emergency eye-wash setups, and record corrective actions instantly when exclusion barriers are breached. Furthermore, supervisors can execute structured digital toolbox talks covering accelerator handling, capturing time-stamped attendance records directly from the field. This digital verification ensures that high-risk processes like underground concrete spraying remain transparent, compliant, and continuously monitored from initial batching to final cure.