Reviewed by
Gavin Owen
Managing Director, ChloroKlean
What is Shock Treatment?
Shock treatment-also known as shock dosing, hyperchlorination, or thermal disinfection-involves applying a high concentration of disinfectant (or high temperature) for a relatively short period to rapidly reduce microbial contamination in a water system.
Typical chemical shock treatments use:
- Chlorine shock: 20-50 ppm free chlorine for 1-2 hours, or 5-10 ppm for 24 hours
- Chlorine dioxide shock: 5-10 ppm for 6-24 hours (lower concentrations needed due to higher efficacy)
- Thermal shock: Water temperature raised to 60°C+ at all outlets for defined periods
Shock treatments are intended as reactive interventions rather than ongoing prevention measures. They may be triggered by positive Legionella samples, contamination incidents, or system changes.
Comparison: Continuous vs Shock Dosing
| Aspect | Continuous Low-Dose | Periodic Shock Treatment |
|---|---|---|
| Approach | Sustained residual throughout system | High dose for short periods |
| Typical concentration | 0.1-0.5 ppm chlorine dioxide | 5-50 ppm (varies by chemical) |
| Biofilm control | Prevents formation; gradual removal | Limited penetration of established biofilm |
| System operation | Normal operation continues | Often requires shutdown or restricted use |
| Material compatibility | Minimal impact at low doses | Can damage seals, gaskets, and pipework |
| Protection duration | Continuous | Temporary; recontamination possible |
| Monitoring requirement | Regular residual checks | Pre/post treatment testing |
Benefits of Continuous Low-Dose Treatment
24/7 Protection
Maintains disinfectant residual at all times, preventing microbial growth between treatments rather than allowing regrowth cycles.
Biofilm Prevention
Low-level residual prevents biofilm from establishing, avoiding the need for aggressive remediation treatments later.
Operational Continuity
No system shutdowns or restricted access. Normal operations continue during treatment without disruption.
Material Protection
Lower concentrations reduce stress on system components, extending the life of seals, gaskets, and pipework.
When Shock Treatment May Be Appropriate
While continuous treatment is generally preferred, shock treatments have a role in specific situations:
Appropriate Scenarios
- Emergency response to confirmed Legionella outbreak
- Commissioning new water systems before use
- After major system repairs or modifications
- Remediation of heavily contaminated systems (as initial step)
- Systems returning to service after prolonged shutdown
Limitations to Consider
- Protection is temporary-recontamination begins after treatment ends
- May not fully penetrate established biofilm
- Can damage system components at high concentrations
- Requires system shutdown or restricted access
- Should be followed by ongoing treatment programme
Combined Approach
Many effective water management programmes combine both approaches:
- Initial shock treatment to address existing contamination or biofilm
- Transition to continuous dosing to maintain control and prevent regrowth
- Periodic enhanced dosing if monitoring indicates emerging issues
The appropriate strategy depends on the system's current condition, risk profile, operational constraints, and regulatory requirements. A competent water treatment advisor can help determine the optimal approach for your specific situation.
Important Safety Information
ChloroKlean products are biocidal products. Always read the product label and Safety Data Sheet before use. Use biocides safely. For advice on treatment strategies, consult our technical team or a competent water treatment specialist.
Related Information
What is ChloroKlean?
Learn about ChloroKlean products, chlorine dioxide technology, and applications.
Read the guideBiofilm Prevention
Understand how chlorine dioxide prevents and removes biofilm in water systems.
Learn more