Manual Cleaning of Caked Salt Sludge in Negative-Pressure Evaporation Chambers Poses Hidden Safety Hazards

I. Risk of Poisoning and Asphyxiation Due to Sudden Release of Toxic Gases

The salt sludge contains dissolved gases such as hydrogen sulfide, volatile organic acids, and ammonia, which are trapped in the crystal crevices under long-term negative pressure and in a sealed environment. When the cover is manually opened and the vacuum is broken, a sudden pressure change causes large amounts of toxic gases to be released instantaneously. This results in local concentrations exceeding safety limits within a short period, posing a high risk of poisoning.

The salt sludge is densely compacted, with a surface salt crust acting as a seal, causing gases to accumulate continuously beneath. When the compacted layer is broken, large amounts of toxic gas erupt instantly without warning.

The chamber is chronically oxygen-deprived, with low internal oxygen levels. Opening the lid creates an oxygen-deficient environment initially; working directly without ventilation and gas replacement can lead to asphyxiation.

II. Chemical Corrosion, Burns, and Damage to Skin and Mucous Membranes

High-salt waste liquids are typically strongly acidic or alkaline; after dehydration and concentration, the salt sludge becomes extremely corrosive. During dredging, shoveling, or breaking up the sludge, mud fragments may fly and splash into the eyes or onto the skin, causing chemical burns.

Dust from chloride ions and sulfide-containing salt sludge can become airborne; inhalation corrodes the respiratory tract, and prolonged exposure damages the skin’s stratum corneum, leading to ulceration.

Salt sludge crystals are hard and sharp; once they cut the skin, corrosive salts continue to penetrate the wound, causing persistent deep corrosion that makes healing difficult.

III. Physical Injuries from Collapses, Burials, and Falling Objects

Thick layers of crusted salt sludge cling to the inner walls and bottom of the chambers. When manually struck to loosen them, large sections may collapse, burying workers.

Hard crystalline blocks and large salt crusts are heavy; when pried loose, they fall vertically, striking the head and torso.

The working space inside the evaporation tank is narrow, and ladders and the tank bottom are slippery; exerting force while prying can easily cause a loss of balance, leading to falls and injuries.

IV. Flammable and Explosive Risks (Wastewater Containing Organic and Sulfide Compounds)

Salt sludge contains organic matter and sulfides; agitation releases flammable volatile gases. Sparks generated by striking with iron tools pose a risk of flash explosions.

Insufficient dust removal and ventilation on-site cause organic dust from the salt sludge to become airborne; if concentrations reach the explosive limit, a dust explosion may occur.

V. Secondary Risks from Structural Damage to Negative Pressure Equipment

Vigorous manual striking or using pry bars to forcefully break up hardened salt blocks can easily scratch or impact the stainless steel passivation layer, leading to subsequent pitting corrosion and leaks; in severe cases, deformation and weld cracking may occur, rendering the equipment unusable.

Forceful prying can cause deformation of the tank body and manhole flanges due to stress, resulting in permanent seal failure and continuous vacuum leakage during subsequent operation.

VI. Secondary Chain Hazards in the Work Environment

Wastewater and salt sludge spilled onto the ground create a high-salt, slippery surface, leading to slips and falls; salt-containing wastewater corrodes the ground and steel platform structures.

The transfer and storage of salt sludge lack containment measures, resulting in leaks of highly saline, corrosive wastewater that contaminates soil and sewer systems, creating environmental liability risks.

Single-person confined space operations without supervision or adequate ventilation make external rescue difficult in the event of an accident, constituting a typical high-risk confined space operation.

VII. Latent Chronic Occupational Health Hazards

Long-term, repeated exposure to salt sludge containing salts, heavy metals, and sulfides, coupled with continuous inhalation of dust, can cause chronic damage to the respiratory tract, liver, and kidneys. These are long-term, latent injuries that are not easily detected immediately.