Cross Contamination Control

Overview

Engineering reference data for Cross Contamination Control in miscellaneous.

Key Formulas

Unit Conversion

$y = x \cdot k$

Multiply by conversion factor.

Linear Interpolation

$y = y_1 + \frac{(x - x_1)(y_2 - y_1)}{x_2 - x_1}$

Estimate between two known points.

Percentage

$p = \frac{\text{part}}{\text{whole}} \times 100\%$

Part as fraction of whole.

Variables

Prevention Methods

Cross-contamination can be prevented by avoiding direct contact between contaminated water and the potable water supply system. The primary engineering controls are:

1. Vacuum Breakers: A device installed in piping or on hose connections. It allows air to enter the system when pressure drops below atmospheric pressure, breaking the siphon and preventing backflow of contaminated water into the supply line.

2. Air Gaps: A physical separation between a water outlet (e.g., a faucet) and the flood-level rim of a receiving fixture (e.g., a sink or tank). This is the most effective method, as it creates an unobstructed vertical space.

3. Check Valves: A mechanical valve designed to allow water flow in only one direction, automatically closing to prevent reverse flow (backflow).

Common Contamination Sources

Direct connections between the potable water system and the following can create a risk of backflow:

• Hoses submerged in polluted water.
• Boilers or equipment using chemically treated water.
• Tanks, baths, swimming pools, or cooling towers.
• Irrigation systems.

Air Gap Requirements

The required minimum air gap distance depends on the fixture outlet size and whether the receiving surface is open (no surrounding walls above the flood level) or closed (has walls).

References

• Original Source