Chloramine Control for Spectators

Overview

Spectator areas in competitive natatoriums face unique air quality challenges from chloramine migration. Trichloramine (NCl₃), the primary airborne contaminant, originates from the pool deck and disperses through buoyancy-driven airflows. Protecting spectators requires engineered barriers and dedicated ventilation to maintain acceptable indoor air quality while minimizing cross-contamination.

ASHRAE Standard 62.1 establishes general ventilation requirements, while the ASHRAE Applications Handbook Chapter 6 provides natatorium-specific guidance. The critical design challenge is preventing chloramine-laden air from the pool deck (elevated temperature, high humidity, contaminant source) from reaching spectator zones through thermal stratification and pressure differentials.

Chloramine Exposure Limits

Trichloramine concentrations must remain below established exposure thresholds:

Exposure Guidelines:

• Occupational limit: 0.5 mg/m³ (8-hour TWA)
• Spectator target: 0.2 mg/m³ (comfort threshold)
• Detection threshold: 0.02 mg/m³ (odor perception)

The relationship between source strength and spectator exposure depends on air exchange effectiveness:

$$C_s = \frac{G \cdot (1 - \eta)}{Q_s \cdot E}$$

Where:

• $C_s$ = spectator zone concentration (mg/m³)
• $G$ = chloramine generation rate at pool surface (mg/hr)
• $\eta$ = barrier effectiveness (0-1)
• $Q_s$ = spectator ventilation rate (m³/hr)
• $E$ = ventilation effectiveness factor (0.5-1.0)

Air Barrier Strategies

Physical Separation

Architectural and mechanical barriers prevent chloramine migration:

1. Elevation differential: Position spectator seating 1.5-3 m above pool deck to exploit thermal stratification
2. Glazing barriers: Full-height glass partitions with sealed joints (infiltration < 0.1 ACH)
3. Air curtains: Vertical jet systems at transitions (discharge velocity 3-5 m/s)

Air Curtain Design:

$$v_j = v_c \sqrt{\frac{\rho_c}{\rho_j}}$$

Where:

• $v_j$ = jet discharge velocity (m/s)
• $v_c$ = crossflow velocity to block (m/s)
• $\rho_c$ = crossflow air density (kg/m³)
• $\rho_j$ = jet air density (kg/m³)

For typical natatoriums with 0.5 m/s crossflow, minimum discharge velocity is 3.5 m/s across a 2.5 m height.

Pressure Relationships

Maintain positive pressure in spectator areas relative to pool deck:

Target Differentials:

• Spectator to pool deck: +2.5 to +5 Pa
• Spectator to exterior: +5 to +7.5 Pa
• Pool deck to natatorium support spaces: -2.5 Pa

Monitor pressure continuously with building automation systems; alarms trigger at ±1 Pa deviation from setpoint.

Dilution Ventilation

graph TB
    A[Pool Surface
Chloramine Source] -->|Thermal Plume| B[Pool Deck Zone
30-32°C, 60% RH]
    B -->|Barrier Interface| C{Air Barrier}
    C -->|Leakage η=0.9| D[Spectator Zone
22-24°C, 50% RH]
    E[Exhaust 8-10 ACH] --> B
    F[Supply 6-8 ACH] --> D
    G[Return Above Pool] --> B
    D --> H[Exhaust Low Level]

    style A fill:#ffcccc
    style B fill:#ffe6cc
    style D fill:#ccffcc
    style C fill:#cce5ff

  

Ventilation Requirements

Spectator Zone Air Change Rates:

Pool Deck Requirements:

• Minimum: 6 ACH with 100% outdoor air
• Typical: 8-10 ACH for competitive facilities
• High-use: 12-15 ACH for intensive training

Dilution Ventilation Calculation

Required ventilation to achieve target concentration:

$$Q = \frac{G \cdot (1 - \eta)}{C_s \cdot E \cdot 3600}$$

Example Calculation:

• Pool chloramine generation: $G = 500$ mg/hr
• Barrier effectiveness: $\eta = 0.90$
• Target spectator concentration: $C_s = 0.2$ mg/m³
• Ventilation effectiveness: $E = 0.8$

$$Q = \frac{500 \cdot (1 - 0.90)}{0.2 \cdot 0.8 \cdot 3600} = 0.087 \text{ m}^3\text{/s} = 184 \text{ cfm}$$

For 500-seat spectator area (volume 5,000 m³), this yields 6.3 ACH—confirming the 6-8 ACH design guideline.

Control Method Comparison

System Design Integration

Supply Air Distribution

Spectator Zone:

• Overhead diffusers with horizontal throw
• Supply temperature 13-16°C below space temperature
• Maximum terminal velocity 0.25 m/s in occupied zone
• Locate returns at low level to capture any infiltrated contaminants

Pool Deck Interface:

• Exhaust at pool surface level (return grilles 0.3-0.6 m above deck)
• High sidewall supply directed across water surface
• Avoid short-circuiting between supply and return

Air Cleaning Supplemental

While source control and dilution are primary strategies, supplemental air cleaning provides additional protection:

Activated Carbon:

• Chloramine removal efficiency: 40-60%
• Media depth: 50-100 mm
• Face velocity: 2.5 m/s maximum
• Replacement: annually or at 50% breakthrough

UV-C Photolysis:

• Effective wavelength: 254 nm
• Dose requirement: 1000-2000 μW·s/cm²
• Placement: in-duct or upper room
• Maintenance: lamp replacement every 12-18 months

Monitoring and Verification

Continuous Monitoring:

1. Differential pressure (pool deck to spectator zone)
2. Temperature stratification (deck vs. spectator)
3. Relative humidity (both zones)
4. CO₂ concentration (occupancy proxy)

Periodic Testing:

• Trichloramine concentration (quarterly)
• Air change rate verification (smoke tests, tracer gas)
• Air curtain velocity profile (annually)
• Barrier leakage rates (annually)

Maintain trichloramine below 0.3 mg/m³ in spectator areas during events. Concentrations exceeding 0.4 mg/m³ require immediate investigation and corrective action.

Source Control Integration

Effective spectator protection begins with minimizing chloramine generation:

1. Water chemistry: Maintain free chlorine 2-4 ppm, combined chlorine < 0.2 ppm
2. Bather load management: Enforce pre-swim hygiene
3. UV or ozone supplemental treatment: Reduce chlorine demand
4. Continuous circulation: 6-8 hour turnover rate minimum

When pool deck concentrations remain below 0.5 mg/m³, achieving spectator targets becomes achievable with standard barrier and ventilation strategies.

References

• ASHRAE Standard 62.1: Ventilation for Acceptable Indoor Air Quality
• ASHRAE Applications Handbook, Chapter 6: Natatoriums
• WHO Guidelines for Safe Recreational Water Environments, Volume 2: Swimming Pools and Similar Environments
• CDC Model Aquatic Health Code (MAHC)