According to NIOSH, confined-space events are typically found to be the direct result of three common factors: a lack of recognition of hazards; a lack of testing, evaluation and monitoring; and a lack of planned rescue procedures.
These can largely be addressed through the proper use and application of two essential pieces of equipment: atmospheric monitors and confined-space blowers or integrated-ventilation systems.
Class A confined spaces are those deemed to be IDLH (immediate dangerous to life or health) environments. The atmospheres in these confined spaces lack natural ventilation and are or have the potential to become untenable.
Before we can make entry into these spaces, OSHA requires that we evaluate and validate the atmosphere with appropriate monitors.
So what is an appropriate monitor? Here are six basic criteria to consider when selecting your monitor.
1. The atmosphere must be tested for oxygen, carbon monoxide, flammability and typically hydrogen sulfide. This requires a four-gas monitor. If the space has a specific hazard — for example many water parks or water recreation facilities will have chlorine hazards present in vaults with pumps — then special sensors can be purchased for the four-gas monitors to detect that specific chemical.
2. All monitors should be equipped with both audible and visual alarms to help alert personnel to the presence of hazardous conditions.
3. OSHA requires that the area to be occupied within the space be tested. The area is defined as a four-foot cube around the area of occupation. This requires the use of a four-gas monitor that is equipped with appropriate-length tubing and pumping capabilities so that samples can be taken prior to entry.
When dealing with confined spaces at depth, this is particularly important. Pumping a layer of the atmosphere into the monitor sensors takes a few seconds. This delay varies between manufacturers and should be a point of evaluation when selecting a four-gas monitor.
4. Monitors should be rugged, environmentally resistant and easily managed. Gas monitors should have some degree of water-drop resistance as well as clips or rigging rings that can take some abuse.
Although many confined spaces are large vault configurations that allow relatively easy movement, some are truly confining and the monitors can take a beating when we are crawling through pipes and openings.
5. Operational sequences should be simplistic and ergonomic. Entrants will often have gloves on and should be capable of operating the gas monitor with relative ease.
Additionally, gas monitors should not encumber operations within the space. The more compact and straight forward the monitor, the happier the entrants.
6. All gas monitors require calibration. Sample gasses as well as the calibration kit should be accessible and affordable. Sending monitors out for calibration can be costly and reduce operational capabilities. Selecting a gas monitor that can be calibrated in house is a more advantageous option.
Atmospheric monitoring should be initiated away from the space to establish hazard zones and progress into the space. This should be done continuously and readings should be documented every five to 10 minutes. Approaching the space with a monitor will help ensure that we don’t jump into the rescue sequence with a lack of hazard recognition.
Venting the space
Once the atmosphere has been tested, consideration turns to ventilating the confined space. In a Class A confined space, ventilation should be applied to purge the atmospheric hazards.
Ventilation in confined spaces can be challenging and should be approached somewhat scientifically to ensure that it is done efficiently and safely. Here are four criteria for developing an effective ventilation equipment cache.
1. Ventilation blowers can be gas or electric as well as nonintrinsic or intrinsically safe. The safest option is to acquire intrinsically safe electric blowers. These have a special plug that prevents the blower from providing a source of ignition in a flammable environment.
Also, electric blowers will not produce CO as a byproduct of combustion, as will the gas-powered versions. This eliminates one more potential problem to manage.
2. Blowers come in a variety of sizes and will produce varying CFMs depending on their design and power. The greater the CFM, the faster the environment can be purged.
The down side of higher-CFM fans is size and weight. Select a blower that is somewhere in the middle between mobility and power.
3. Develop an assortment of ductwork, manhole saddles, and 90-degree bends. Every twist, turn, and tight corner in a confined space can dramatically alter the effectiveness of a ventilation operation if you are not maximizing airflow.
Look for ductwork and accessories that have good cinching mechanisms to insure that they don’t come apart once they are under pressure. Remember that each accessory reduces the fan’s CFM but the reduction is far less than that from a compressed kink in a hose that should have a rigid 90-bend accessory.
The manhole saddle accessories will also facilitate movement in and out of the space without disrupting airflow. When these reduction saddles aren’t used, ductwork often has to be removed to allow entrant access and egress.
Spaces at depth will also require extensive ductwork. Remember that a four-foot atmospheric cubicle must be maintained around the entrants. Additionally, atmospheric hazards that are heavier than air will be at the bottom of the confined spaces and will not be adequately purged with the appropriate placement of ductwork.
4. Ventilation can be performed with negative pressure, positive pressure or both. The weight and characteristics of the atmospheric hazard as well as the environmental conditions of the general area will dictate the type(s) of ventilation applied.
Selecting a blower that can be used in a positive- and negative-pressure application is ideal. It is also important to note that multiple blowers are the goal.
Many spaces may require multiple blowers used in different configurations to avoid short circuiting. The more options you have, the better equipped you will be to address the problem.
Purge-time calculations
Purge-time calculations are frequently overlooked in confined-space ventilation, but should not be. Generally speaking, this is the time required for the air in the confined space to recirculate approximately 7.5 times. This benchmark should eliminate the presence of atmospheric hazards or at least reduce them to something tenable.
This is a relatively accepted benchmark and is calculated by dividing the cubic volume of the confined space by the CFM of the blower. Multiply this number by 7.5 to find the time required.
This calculation will help evaluate the effectiveness of ventilation operations through trending of atmospheric readings and their correlation to time. It also develops a tactical benchmark for projected time of entry.
There are a myriad of other considerations when performing confined-space operations, but understanding these two vital pieces of equipment and applying them correctly will have you on the fast track to safe and effective operations.
