These hazards are obvious, and industryâ€™s workers would not even consider doing the work without utilizing the proper personal protective equipment (PPE). There is one hazard, however, that looms as perhaps the greatest danger â€” one that can have catastrophic results if not understood and dealt with in a safe manner â€” unseen hazards from gases.
Prior to entering any confined space, one must determine if the environment is safe for human entry and safe to commence with the task at hand. To better understand what is needed letâ€™s first look at the definition of a confined space. OSHA in its Federal Register, 29 CFR 1910.146, defines a confined space as any space that has limited openings for exit or entry, poor natural ventilation, not designed for continuous worker occupancy, or has the potential for hazardous environments. This criterion broadens the scope of confined spaces from anything from an open top digester, to a traditional vault, sump or manhole.
Often referred to as â€œhot work,â€ the entrant must first evaluate the space prior to entry. This is done with a direct reading, calibrated multi-gas monitor. The Federal Register goes on to further stipulate that the confined space must be checked for levels of oxygen, combustible gas (LEL gases), and any toxic gas specific to the industry. This must be done at four-foot levels, in any direction of travel, throughout the confined space. The levels were established because often gases stratify within a stagnant confined space. Heavier gases accumulate at the bottom while lighter gases gravitate to the top.
Oxygen can be reduced naturally in a confined space due to oxidation and/or bacterial activity. You may think if a little oxygen is good then more is better, but this is not the case. Elevated oxygen levels above 23.5 percent can increase the risk of enhanced combustion, which causes items that are normally not combustible to combust. Excessive oxygen enhances the combustion process as evidenced by the reaction you get when you turn up the oxygen on an oxy/acetylene torch.
It is for these reasons that the oxygen content in a confined space must remain between 19.6 percent and 23.4 percent in order for safe entry and occupation to commence.
All combustible gases have their own unique LEL levels. For example, methane explodes at 5.0 percent by volume while pentane combusts at 1.5 percent by volume. This level equates to 100 percent LEL or the minimum level of gas needed to cause an explosion. A reading of 50 percent LEL would mean that you would have half of the concentration of combustible gas needed to cause an explosion.
The OSHA allowable level for combustible gas is 10 percent LEL, which is a very conservative level but it does indicate that a combustible source is available and levels need to be continuously monitored to ensure they do not increase.
Common industrial toxic gases include carbon monoxide and hydrogen sulfide. Carbon monoxide (CO) is a by-product of incomplete combustion and can be present in a confined space adjacent to a combustion source. Furthermore, carbon monoxide can be generated in the welding or cutting process due to the work being done. Hydrogen sulfide (H2S) is a by-product of decomposition and commonly appears in petroleum and waste water applications.
The toxic gas family is not limited to these two gases; there are many other industry- and process-specific chemicals that fit into this category. It is always a good practice to fully understand the industry you are serving and the potential toxic gases that could be present. Most multi-gas monitors accommodate a variety of toxic sensors that can be easily plugged in and calibrated to be gas-specific. Utilizing this capability customizes your gas monitor to address the industry-specific hazards at hand.
When welding in confined spaces, a multi-gas monitor is as vital as protective gloves and a face shield. By including this critical tool in your toolbox, you will not only increase your level of safety, but youâ€™ll also enhance your peace of mind. Youâ€™ll breathe easier because welding safety is more than just guarding against arcs and sparks.