Ventilating Confined Spaces

Every confined space rescue carries two key truths. They are low-frequency events that pose great risk. Because of their low frequency, however, rescuers can be unprepared for hidden hazards, especially those posed by harmful particulates or gases in the air. 

A confined space is an enclosed area that poses a risk of death or serious injury from hazards or harmful atmospheric conditions. These spaces include reaction vessels, storage tanks, silos, sewers, combustion chambers and more. They can even include unventilated or poorly ventilated rooms.

The atmospheric conditions in these tight spaces threaten rescue officials and victims. The biggest risk in every confined space rescue is a lack of oxygen. Firefighters must monitor oxygen levels within confined spaces to protect themselves and get life-saving equipment to victims if necessary. 

Poisonous gases, fumes or vapors also present risk, as can liquids or solids that fill the space or release gases into it. Excess oxygen and flammable vapors in the area can cause fires and explosions.

Rescuers can protect themselves and victims by shutting off the sources contaminating the air and by using respiratory protection. Purging toxic gases from a confined space before entry presents another means of avoiding asphyxiation.

Monitor the Air

Before entering any confined space, rescuers must consider the atmosphere within. Testing the air for oxygen, carbon monoxide, flammability and hydrogen sulfide can save lives.

Monitor atmospheric conditions with a rugged, four-gas monitor equipped with audible and visual alarms that alert personnel to unsafe conditions. The best monitors allow rescuers to operate them with gloves on.

Remember to calibrate monitors regularly to ensure sensors accurately read calibration gas concentrations. OSHA recommends following manufacture’s guidelines for calibration frequency. Practitioners, however, recommend calibrating monitors at least every three to six months; more often in critical operations.

Begin by monitoring the area directly outside, then proceed into the confined space. Monitor continuously and document findings every 5-10 minutes. Using a monitor in this manner ensures personnel fully understand atmospheric conditions before entry.

Ventilate the Space

Ventilation can improve a toxic atmosphere, replace contaminated air, reduce risk for explosion or fire, lower the temperature in the space, and increase operator and victim comfort levels. Rescuers can rely on one of two ventilation methods: purging or inerting.

Purging: This ventilation method allows rescuers to eradicate existing contaminants by displacing the hazardous atmosphere with another medium, like air, water, steam or inert gases. One of the simplest ways to purge is to let the outdoor air in. Opening doors and windows can increase oxygen circulation within a space.

But often that’s not possible or enough. The type of toxins involved dictates the medium to use. Sometimes using mechanical forced air ventilation may work better. These units draw air from one area, compress it and direct it into the confined area. Rescuers can use grounded air movers powered by compressed air or electric fans or blowers to force fresh air into the area. Make sure a third-party testing lab has rated any air mover used as explosion-proof in a flammable or combustible atmosphere.

Inerting: This ventilation method pushes inert gases like nitrogen (N2) and carbon dioxide (CO2) into a confined space to remove excess oxygen. Removing oxygen reduces fire and explosion hazards by lowering oxygen levels to where they cannot support combustion. When relying on inerting, it is crucial to ventilate with fresh air to return the area to normal atmospheric conditions.  

Consider Purge Times!

Successful ventilation requires rescuers to understand purge times, or the time required to remove contaminants. Purge times can vary, depending on contaminant levels and concentration, and the capacity of air movers.

To calculate purge times, rescuers must know the cubic footage of the confined space (length x width x height), then divide it by the CFM displacement of the blower. The calculation will help determine how long a blower must run to achieve a single air exchange. Some experts recommend at least seven air changes in the space prior to entry. 

The above calculation assumes an ideal mixing and distribution of supplied air. Some situations will demand longer purge times for proper ventilation. 

Prevention & Preparation

It’s said that prevention is worth a pound of cure. Long before anyone needs rescue, facilities should establish programs that ensure ventilation equipment works well.

Every workplace has ventilation systems designed to filter out bad air and replace it with fresh air. Make sure these systems always operate properly. Establish a schedule that ensures regular operational checks of these vital systems.

Regularly check filters on all ventilation systems. Perform this routine maintenance on all air conditioning units and air purifiers. Set up checks and balances to ensure the work gets done.

Remember to test monitors and air movers for proper operation. Having this equipment means little if it won’t function during an emergency. Calibrate monitors every three to six months to ensure sensors accurately read calibration gas concentrations.

Finally, train and train often for these events, however infrequent they may be. Confined space training helps rescuers recognize hazards and work safely in and around these spaces. Provide this training to any individual expected to make rescues in confined spaces with a hazardous atmosphere. Regular practice makes perfect. It ensures rescue teams know what to do and can perform smooth rescues automatically when disaster strikes.