Sterilization Time for Formulin (Formaldehyde/Paraformaldehyde) Tablets
For cold sterilization using paraformaldehyde tablets (Formulin), the required exposure time is 15 to 24 hours at a concentration of 10 tablets per cubic decimeter (dm³) with 80% relative humidity. 1
Exposure Time Requirements Based on Application
The sterilization time for formaldehyde tablets varies significantly depending on the intended purpose:
Cold Sterilization (Full Sterilization)
- Exposure time: 15-24 hours 1
- Concentration: 10 tablets/dm³ 1
- Relative humidity: 80% (mandatory requirement) 1
- This method should only be used when heat sterilization methods (steam autoclave, dry heat, or chemical vapor) are not feasible for the specific device or instrument 1
Disinfection (High-Level)
- Exposure time: Minimum 5 hours 1
- Concentration: 10 tablets/dm³ 1
- Objects must not be heavily contaminated or soiled 1
- This is distinct from sterilization and provides a lower level of microbial kill 1
Bacterial Count Reduction and Storage
- Exposure time: Minimum 3 hours 1
- Concentration: 1 tablet/dm³ 1
- Suitable only for maintaining already-sterilized instruments in storage 1
Critical Implementation Requirements
Container specifications are essential for effectiveness:
- Use only tight-fitting containers such as instrument cabinets, Heynemann cabinets, catheter boxes, or sealed plastic bags 1
- Poor container sealing will result in formaldehyde gas escape and sterilization failure 1
Environmental conditions:
- 80% relative air humidity is absolutely required for paraformaldehyde tablets to function properly 1
- Without adequate humidity, the tablets will not depolymerize effectively and sterilization will fail 1
Important Limitations and Safety Considerations
This method is considered an expedient, not a preferred sterilization technique 1. Modern guidelines strongly favor heat-based sterilization methods:
- Steam autoclaving at 121-132°C remains the gold standard for heat-stable instruments 2
- Dry heat sterilization at 170°C for 1 hour is preferred for items that cannot be autoclaved 2
- Chemical sterilization with liquid agents (glutaraldehyde, hydrogen peroxide, peracetic acid) may require up to 10 hours of immersion but is more reliable than formaldehyde tablets for heat-sensitive items 2
Chemical hazards:
- Formaldehyde is a hazardous chemical by nature, and employers must ensure safe work environments with appropriate exposure monitoring 3
- Modern sterilizers are designed to contain these chemicals safely, but leaks can occur through mechanical failure or user error 3
Verification of Sterilization
Regardless of the method used, biological indicators (spore tests) should be performed at least weekly to verify that sterilization has been achieved 2. Chemical indicators alone are insufficient to confirm sterility 2.
Alternative verification for formaldehyde sterilization:
- Research has demonstrated that test strips with Bacillus subtilis spores or Mycobacterium phlei cells can verify formaldehyde sterilization effectiveness 4
- Vaporization of 2 ml formalin per 0.028 m³ followed by 18-hour exposure at ambient temperature showed 100% success in killing these test organisms 4