Refinery Cooling Towers Face a Stealth Risk. ASHRAE 188 Shows How to Control It.

Legionella pneumophila—bacteria that cause Legionnaires’ disease—prefers 20–50 °C water and stagnation, conditions found in many cooling systems (pmc.ncbi.nlm.nih.gov). Untreated towers can aerosolize Legionella, and legionellosis (severe pneumonia) often carries ~10–15% fatality (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov).

The risk is not hypothetical: a 1976 hotel outbreak caused >200 cases and 34 deaths, reported US cases have quadrupled since 2000 (pmc.ncbi.nlm.nih.gov), and the EU/EEA hit a record 10,700 cases (2.4 per 100k) in 2021 (www.ecdc.europa.eu). International standards (e.g. ASHRAE Standard 188) and CDC/WHO guidelines emphasize a comprehensive water management program (WMP).

In Indonesia, formal Legionella regulations are limited, but the Ministry of Health lists legionellosis as an emerging threat; best practice follows established WMP guidance (e.g., CDC toolkit pages). In refining, that means chemistry, disinfection, mechanical hygiene, and documentation are treated as critical controls, not afterthoughts.

ASHRAE 188 water management program

An ASHRAE 188‑aligned WMP (water management program) documents team roles, a full system schematic, hazard analysis, and control measures. Key risk factors—temperature, sediment/biofilm, water age, and disinfectant residual—are identified for each tower (pmc.ncbi.nlm.nih.gov) (www.cdc.gov). Routine environmental assessments map piping, sumps, disinfectant feed points, drift eliminators (devices that reduce aerosol drift), and low‑flow areas; make‑up water quality and process contaminants are noted as nutrient sources.

Control strategies set measurable limits and verification actions. CDC emphasizes that scale, corrosion, and sediment controls (i.e., cleaning) are critical; automated corrosion/scale inhibitors and coagulation are used to maintain clear water (www.cdc.gov). In practice this often pairs a corrosion inhibitor and a scale inhibitor with dispersants; for example, a refinery may standardize on scale inhibitors for mineral control and corrosion inhibitors for metallurgy protection.

WMP verification typically includes continuous monitoring of parameters like pH (acidity/alkalinity), conductivity, and disinfectant residual, with automated sensors and logs. Automated feed equipment such as an accurate dosing pump and a documented cooling tower chemical program help keep residuals inside control limits.

Biocide dosing strategy and controls

A robust biocide regimen is central to suppressing Legionella. Cooling towers commonly use oxidizing biocides (chlorine, bromine, chlorine dioxide; oxidizing biocides release active oxidants) plus dispersants to limit biofilm. CDC recommends automated, continuous feed and monitoring to maintain target residuals (www.cdc.gov), often 24/7 dosing targeting a steady residual on the order of 1–3 mg/L free chlorine (final setpoints guided by the chemical supplier). Non‑oxidizing biocides (e.g., isothiazolones; non‑oxidizers disrupt cell functions without oxidation) can be rotated or added as supplemental slug treatments to penetrate biofilms. Refineries track chemical use and residuals against control limits; automated controls help prevent under‑ or over‑dosing. A program like this is typically anchored by proven biocides and supported with dispersant chemicals.

During response disinfection or an outbreak scenario, CDC advises circulating water and adding an oxidizing biocide to reach ≥20 ppm free Cl₂, then holding it (often 24 h) (www.cdc.gov). Maintaining residuals (e.g., ≥10 ppm Cl₂ for ≥24 h post‑shock; pH 7.8–8.5 for chlorine/bromine systems) is prescribed to maximize kill (www.cdc.gov). Data‑backed outcomes are strong: studies show shock+continuous protocols reduce Legionella levels by >98% (pmc.ncbi.nlm.nih.gov), and a European refinery tower with ~10⁵ CFU/L (colony‑forming units per liter) saw counts drop to ~10² CFU/L after two 20 ppm chlorine shocks plus continuous chlorination (pmc.ncbi.nlm.nih.gov).

Cleaning and mechanical hygiene

Physical cleaning removes biofilms, sediments, and scale that shield Legionella. CDC toolkits call for at least annual offline cleaning—removing the tower from service to drain, scrub internals (fill media, basin, nozzles), and disinfect—then returning it to operation (www.cdc.gov). Many facilities clean more often (semi‑annually or quarterly) in high‑contamination settings. Professional support such as a scheduled cooling tower cleaning service can standardize scope and documentation.

Chemistry and cleaning are complementary; without cleaning, high oxidant levels can leave reservoirs of bacteria. One review found Legionella in 66.7% of municipal water storage‑tank sediments (www.ncbi.nlm.nih.gov), which led AWWA to mandate tank draining/inspection at least every 3 years. If routine testing or any illness suggests proliferation, CDC prescribes a “shock and flush”: reach 20+ ppm sanitizer, circulate, then purge and neutralize before return to service (www.cdc.gov) (www.cdc.gov). Systems should not be returned to service until disinfectant traces are absent and a satisfactory test is obtained.

Routine monitoring and testing

Continuous monitoring of tower function and water chemistry underpins the WMP. Typical logs capture pH, conductivity, corrosion inhibitor, scale inhibitor, and biocide residual (daily or per shift). Drift eliminators and sumps are kept free of obstructions, and sensors are calibrated with documented maintenance.

Microbiological testing validates program efficacy. CDC notes that routine (periodic) sampling helps establish a baseline and “validate the water management program” (www.cdc.gov). For high‑risk sites (e.g., past cases or immunocompromised personnel), monthly or quarterly culture testing is prudent. Samples typically use 250 mL (milliliters) (www.cdc.gov) from basins and critical recirculation points. Laboratory culture or PCR (polymerase chain reaction, a DNA method) guides actions; while no universal safe level exists, many jurisdictions trigger an investigation or disinfection around ~1,000 CFU/L. Exceedances prompt remedial cleaning and re‑treatment, followed by confirmatory testing.

Performance metrics and business impact

Outcomes are measurable: consistently low or non‑detect Legionella counts, no outbreaks, and compliance with chemistry targets. Plants adopting ASHRAE 188‑style WMPs have reported an ~80–100% decrease in positive Legionella findings over a year versus uncontrolled systems (case studies in industry reports). Regulators’ reports in other countries indicate that tower inspections and disinfection compliance drastically reduce LD cases. Another example cited: a European manufacturer dropped Legionella from ~10⁵ CFU/L to <10² CFU/L after tightening its biocide and cleaning schedule (pmc.ncbi.nlm.nih.gov).

Lapses carry consequences: a 2015 US outbreak was traced to a neglected condo tower. Beyond health impacts, the cost of an outbreak (health care, lawsuits, lost production) can be tens to hundreds of times higher than a rigorous maintenance program. The measurable outcome of a strong plan—integrating tight biocide dosing, cleaning, and testing with records—is health protection and economic savings. Recent guidance in healthcare and high‑risk facilities shows that sustained WMPs virtually eliminate legionellosis incidents (www.cdc.gov) (www.cdc.gov). Applying these same standards in refinery cooling systems similarly minimizes risk—turning Legionella from a disaster liability into a managed hazard.

For programs that rely on chemistry, aligning feed and monitoring with an accurate dosing pump helps maintain residuals, and sourcing appropriate cooling tower chemical packages keeps the system within control limits without over‑ or under‑dosing.

References and sources

References: High-quality sources across multiple countries emphasize the above practices. For example, CDC’s Controlling Legionella in Cooling Towers module explicitly lists scale/sediment control and automated disinfectant management as critical (www.cdc.gov), and mandates annual offline cleaning of towers (www.cdc.gov) (www.cdc.gov). A peer‑reviewed tower‑study found that shock chlorination plus continuous treatment yielded a 98% reduction in Legionella counts (pmc.ncbi.nlm.nih.gov). International bodies note rising LD trends (e.g. EU/EEA 2021 data www.ecdc.europa.eu, US trends pmc.ncbi.nlm.nih.gov) that justify rigorous programs. Indonesian health authorities likewise list Legionella among emerging pathogens, implying the need for vigilance (e.g. FAQs on legionellosis on the Kemkes site).

Sources: CDC guidance (Cooling Towers Module, 2025; Routine Testing, 2025) (www.cdc.gov) (www.cdc.gov) (www.cdc.gov) (www.cdc.gov) (www.cdc.gov); Iervolino et al. 2017 (Int. J. Environ. Res. Public Health) (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov); MacIntyre et al. 2018 (Emerg. Microbes Infect.) (pmc.ncbi.nlm.nih.gov); ECDC 2023; NASEM 2019; etc.