When using hose streams for vapor dispersion, responders must be aware that which statement is true?

When using hose streams for vapor dispersion, responders must be aware that which statement is true?

• A. Reducing concentration may bring vapors into flammable range
• B. Hot zone unaffected by vapor dispersion
• C. Hose streams cannot affect vapor concentration
• D. Vapors always stay above LEL when dispersed

Answer: (A)

Dispersing vapors with a hose stream changes the vapor concentration in the air around the plume. The water flow creates turbulence and entrains air, mixing the vapor with fresh air in uneven ways. As a result, diluting the vapor can actually move the concentration into the flammable range (between the LEL and UEL) in parts of the plume or at the plume’s edges. So, even though you’re “reducing” overall vapor, you may unintentionally produce pockets of vapor that are capable of ignition. That’s why the statement about reducing concentration potentially bringing vapors into the flammable range is the true one. Vapors can also be transported or linger in ways that affect the hot zone, and hose streams can influence vapor concentration rather than being unable to affect it, and vapors don’t always stay above the LEL as they disperse.

Dispersing vapors with a hose stream changes the vapor concentration in the air around the plume. The water flow creates turbulence and entrains air, mixing the vapor with fresh air in uneven ways. As a result, diluting the vapor can actually move the concentration into the flammable range (between the LEL and UEL) in parts of the plume or at the plume’s edges. So, even though you’re “reducing” overall vapor, you may unintentionally produce pockets of vapor that are capable of ignition. That’s why the statement about reducing concentration potentially bringing vapors into the flammable range is the true one.

Vapors can also be transported or linger in ways that affect the hot zone, and hose streams can influence vapor concentration rather than being unable to affect it, and vapors don’t always stay above the LEL as they disperse.