Hygroscopic chemicals pose significant occupational health risks that extend far beyond their primary industrial applications. These substances actively absorb moisture from the air, which substantially increases their potential for causing skin damage and respiratory injuries in industrial environments. Understanding the nature of these hazards and implementing comprehensive control strategies is essential for protecting workers and maintaining regulatory compliance in facilities handling such materials. 

Understanding Hygroscopic Chemicals and Their Hazards 

Hygroscopic chemicals are substances that readily absorb water vapor from the atmosphere. When exposed to humid conditions, they accumulate moisture, which can trigger chemical reactions, increase deliquescence (dissolution), and dramatically amplify their corrosive and irritant properties. The most common hygroscopic chemicals encountered in industrial workplaces include: 

• Calcium chloride (CaCl₂) 

• Sodium hydroxide (NaOH) 

• Potassium hydroxide (KOH) 

• Sulfuric acid (H₂SO₄) 

• Acetic anhydride 

• Copper sulfate (CuSO₄) 

• Various metal salts and phosphorus compounds 

The hygroscopic nature of these chemicals creates compounding dangers. As they absorb moisture, anhydrous forms can become highly deliquescent—literally dissolving into liquid form. This transformation intensifies their corrosive properties and increases the bioavailability of toxic metal contaminants, thereby elevating worker exposure risks significantly. 

Respiratory Hazards and Health Effects 

Respiratory exposure to hygroscopic chemicals occurs when workers inhale aerosolized particles or vapors. The moisture-absorbing properties of these substances directly influence how deeply they penetrate the respiratory system. Research demonstrates that hygroscopic particles undergo significant size expansion at the elevated humidity levels found in human airways (typically 99.5% relative humidity), which dramatically alters their deposition patterns within the lungs. 

Acute respiratory effects include: 

• Irritation of the nose, throat, and mouth 

• Coughing and shortness of breath 

• Laryngeal swelling 

• Bronchial inflammation 

• Potential chemical pneumonitis with severe exposure 

Chronic health consequences may involve: 

• Persistent respiratory irritation 

• Sensitization and allergic responses 

• Reduced lung function over time 

• Development or exacerbation of occupational asthma 

• Increased susceptibility to respiratory infections due to mucous membrane damage 

The hygroscopic growth of particles is particularly concerning because particles in the 0.1 to 1 micrometer range—exactly where hygroscopic growth has the most dramatic effect—penetrate most efficiently into the pulmonary airways. Studies show that humidification of inhaled particles can increase deposition fractions by 171% to 261% in critical respiratory regions, meaning far more toxic material reaches deep lung tissue than would in dry conditions. 

Skin Contact Hazards 

Direct skin contact with hygroscopic chemicals poses severe occupational health risks. Many hygroscopic substances are highly corrosive, and their moisture-absorbing properties make these effects progressively worse as exposure time increases and atmospheric humidity rises. 

Skin injury mechanisms include: 

• Chemical burns and tissue necrosis from strong acids and bases 

• Severe irritation and dermatitis even from brief contact 

• Development of allergic contact dermatitis with sensitization 

• Penetration through damaged skin barriers into systemic circulation 

• Secondary infections from compromised skin integrity 

Particularly concerning is acetic anhydride, which can cause severe skin burns, potential eye damage, and may trigger allergic sensitization. Workers exposed to acetic anhydride may develop skin allergies that result in rashes and itching upon minimal future exposure. Additionally, workers handling metal-containing hygroscopic compounds in humid environments face accumulation of toxic metals on skin surfaces, increasing absorption risks. 

Comprehensive Exposure Control Strategies 

1) Engineering Controls and Ventilation

Engineering controls represent the most effective and reliable method for managing hygroscopic chemical hazards and should always be implemented first. 

• Chemical fume hoods: Essential for all work with volatile hygroscopic chemicals; must have certified adequate face velocity (typically 80-120 linear feet per minute) and continuous airflow monitoring 

• General laboratory ventilation: Maintain negative pressure in work areas relative to adjacent spaces to prevent vapor migration; aim for 6-12 air changes per hour 

• Local exhaust systems: Capture vapors at their source; particularly important for operations generating significant aerosol or dust 

• Glove boxes and containment devices: Suitable for handling particularly hazardous hygroscopic substances with maximum control requirements 

All engineering controls require annual certification and regular inspections. Fume hoods must be inspected quarterly for face velocity, and airflow monitors should be checked continuously during use. 

2) Humidity and Environmental Controls

Controlling workplace humidity directly reduces the hygroscopic chemical hazard. 

• Install dehumidification systems to maintain relative humidity below 50% where feasible 

• Ensure adequate ventilation in storage and work areas to prevent moisture accumulation 

• Monitor and record humidity levels continuously in high-risk areas 

• Store hygroscopic chemicals in sealed, moisture-proof containers with desiccant packets 

• Use secondary containment with absorbent materials that capture moisture 

3) Work Practice Controls

Administrative and procedural controls complement engineering measures and reinforce safe practices. 

• Minimize the quantity of hygroscopic chemicals in use; employ microscale or reduced-scale experiments when possible 

• Establish designated work areas with clear signage warning of specific hygroscopic chemical hazards 

• Prohibit eating, drinking, and smoking in areas where hygroscopic chemicals are handled 

• Implement strict hand-washing protocols before breaks and at shift end 

• Train personnel to immediately report spills and to contain them using appropriate absorbent materials 

• Rotate workers to limit cumulative exposure during extended operations 

• Use proper chemical handling techniques that minimize aerosolization 

Personal Protective Equipment Selection 

PPE serves as the final layer of protection when engineering and work practice controls cannot eliminate exposure. Employers must assess workplace conditions and select appropriate equipment levels. 

1. Respiratory Protection

• Air-purifying respirators (APRs): Appropriate when substance type is known, concentrations are measured below actionable levels, and skin contact is unlikely; requires proper cartridge selection and fit-testing 

• Supplied air respirators: Required for unknown atmospheres, high concentrations, or conditions where APRs are inadequate 

• Fit testing: Mandatory annually and whenever respirator type or wearer changes 

• Medical clearance: Required before workers use respiratory protection; must be documented in employee files 

2. Skin and Eye Protection 

Critical PPE Considerations: 

• Never rely on contact lenses when working with corrosive hygroscopic chemicals 

• Inspect all PPE before each use for damage, contamination, or deterioration 

• Use only NIOSH-approved respiratory protection equipment 

• Establish a replacement schedule for degradable PPE items 

• Train employees thoroughly on proper donning, doffing, and care procedures 

Monitoring and Compliance Requirements 

i) Exposure Monitoring

Employers must establish baseline exposure measurements and conduct periodic monitoring to ensure compliance with Permissible Exposure Limits (PELs) and Workplace Exposure Limits (WELs). 

ii) Medical Surveillance

• Establish baseline health assessments before workers begin handling hygroscopic chemicals 

• Provide opportunity for medical examination if workers exhibit symptoms of exposure 

• Document all occupational health concerns and track exposure-related complaints 

• Implement routine monitoring for workers in high-exposure roles 

Chemical Storage and Inventory Management 

Proper storage practices directly reduce exposure risks by minimizing moisture contact and preventing accidental releases. 

• Store hygroscopic chemicals in original containers with intact labels and Safety Data Sheets 

• Use designated storage areas with adequate ventilation separate from general workplace areas 

• Maintain temperature between 60-75°F; avoid locations exposed to direct sunlight or heat sources 

• Implement FIFO (first-in, first-out) inventory rotation to ensure older chemicals are used first 

• Conduct weekly inspections for container integrity, leaks, or crystallization 

• Keep chemical storage areas locked and restrict access to trained personnel only 

• Use secondary containment for all liquid hygroscopic chemicals 

Employee Training and Information 

Effective hazard communication is fundamental to preventing hygroscopic chemical injuries. 

Training program requirements: 

• Initial orientation covering the specific hygroscopic chemicals handled and their unique moisture-related hazards 

• Detailed review of all relevant Safety Data Sheets, with particular emphasis on Section 2 (Hazard Identification) and Section 8 (Exposure Controls) 

• Proper use and limitations of engineering controls, particularly fume hood operation and verification 

• Correct donning, use, and inspection procedures for all assigned PPE 

• Emergency response procedures including eye wash station and emergency shower usage 

• Decontamination and cleanup protocols for spills and exposures 

• Recognition of early symptoms of acute exposure requiring immediate medical attention 

• Annual refresher training with updates on new processes or equipment 

Documentation of all training must be maintained and reviewed at least annually to verify employee understanding. 

 

Conclusion 

Preventing skin and respiratory injuries from hygroscopic chemicals requires a multi-layered approach combining engineering controls, environmental management, proper work practices, appropriate PPE, rigorous monitoring, and comprehensive training. Organizations that prioritize this comprehensive strategy—rather than relying solely on PPE as a primary control—create safer workplaces and maintain regulatory compliance while protecting worker health and productivity. Regular assessment of control effectiveness, coupled with continuous employee education, ensures that hygroscopic chemical hazards remain well-managed throughout facility operations.