Author(s): Nancy Pearce. Published on March 1, 2017.

Tight Spot

To address a galaxy of hazards related to confined spaces, NFPA creates a new guide for safe confined space entry and work


On average, two people will go to work this week somewhere in the United States and not return home to their families as a result of entering a confined space. According to the annual Census of Fatal Occupational Injuries, compiled by the Bureau of Labor Statistics, 136 U.S. workers died in incidents associated with confined spaces in 2015.

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Fatalities in confined spaces are regularly reported in the news, although the public may not recognize them as confined space incidents. Confined spaces and their hazards vary—there are different types of confined spaces and confined space hazards. They’re found not only in industrial settings but in nearly every workplace, including commercial facilities, hospitals, universities, and even on farms. On a farm in Michigan in 1989, five members of the same family, representing three generations, died as one after another entered a manure pit in an attempt to save their relatives. The incident was repeated in 2012 in Pennsylvania when a father and his two sons died in a manure pit.

Confined spaces are those that are large enough to enter and perform work inside; have a limited or restricted means of entry or exit; and are not designed for continuous human occupancy. They include various types of tanks, cargo holds on ships, silos, utility vaults, boilers, sewer and water manholes, elevator shafts, dumpsters, tunnels, and more. The deaths and injuries that occur in these spaces are the result of hazards ranging from entrapment and drowning to asphyxiation and toxic chemical exposure.

History of entry into a space without incident is not a good indicator that a space is safe; it is not uncommon for workers to die in spaces that have been entered previously for many years without incident.

In many of these incidents, it is not just the person entering the confined space who dies, but also the “rescuer” who may be unaware of the hazard. In January in Key Largo, Florida, a private contractor who was fixing a roadway climbed into a 15-foot-deep hole to investigate complaints of sewage backups in the neighborhood. Reportedly the first man went in and lost contact with his coworkers above. A second worker climbed down in search of the first, and also lost contact. A third man then went down in a desperate search to find his coworkers. Fearing the men were unconscious, a volunteer Key Largo firefighter attempted to rescue the downed workers.

He entered the hole without a self-contained breathing apparatus because the space was so narrow, and became incapacitated within seconds. The firefighter eventually recovered, but the three workers perished. The space was later tested and found to contain elevated levels of methane and hydrogen sulfide as well as decreased oxygen levels, likely the result of decaying organic material and rusting metal. To address the hazards that accompany confined spaces, NFPA recently created a new document, NFPA 350, Safe Confined Space Entry and Work. The guide, released last year, provides guidance on the best safety practices that can be used by employers, employees, facility owners, and rescue personnel to assist in the identification, evaluation, and control of confined space hazards. It addresses gaps not covered in existing regulations, simplifies confined space terminology, and provides guidance on competencies for those who work in and around confined spaces.


Confined spaces contain a wide range of hazards that are usually designated as either physical or atmospheric in nature. Their limited means of entry and exit and the fact they are not designed for continuous human occupancy means they often contain physical hazards that would not exist in normally occupied spaces, such as exposed energized electrical equipment that could lead to shock or electrocution, and mechanical hazards such as rotating or moving parts that could lead to crushing or amputation. Additional physical hazards may include engulfment with solid or liquid materials such as grain or water. Some of these spaces are narrow or tapered, which can lead to entrapment.

Confined spaces often are poorly ventilated, since they have limited openings, and are not designed for people to routinely work in. Atmospheric hazards in these spaces may exist due to materials stored in them previously, such as chemical storage tanks. Many atmospheric hazards are less apparent, however, and are the result of decay of simple organic material such as leaves or residue at the bottom of a tank that can create an oxygen deficiency, flammable gases such as methane, and toxic substances such as hydrogen sulfide. Fatalities may also result in an oxygen-deficient environment that occurs due to rusting metal. Confined spaces can also contain hazards such as falls, slippery surfaces, noise, and extreme temperatures.

Those are just the hazards inherent to the spaces—hazards can also exist adjacent to a space that can impact worker safety, such as engine exhaust entering a space from nearby operations or the hazard that occurs when a cover on a confined space is removed and releases toxic materials into the air above and around the opening. Hazards may also be introduced into a space and may include chemical cleaners, paints, and welding equipment depending on the work being done. Hazards in confined spaces can vary from day to day, requiring entry procedures to change correspondingly; for example, entering a vault to check a gauge requires different procedures than entering that same vault to conduct welding on a pipe. For this reason, confined space hazards must be evaluated each time an entry occurs to determine if controls are needed.

To address this daunting array of spaces and hazards, three key standards are used in confined space entry in the U.S.—OSHA 1910.146, “Permit Required Confined Spaces”; ASSE Z117.1, Safety Requirements for Confined Spaces; and OSHA’s new 1926 Subpart AA, Confined Spaces in Construction. These standards provide minimum performance-based requirements, though it’s important to note that performance-based standards focus primarily on the desired outcome—in this case, preventing injuries and fatalities in confined spaces.

Where performance-based standards are sometimes lacking is in offering sufficient guidance on how to reach those desired outcomes. This is where NFPA 350 comes in, providing many of the “how-to” points for confined space safety that will help employers comply with one of the performance-based confined space standards. For example, OSHA standards require hazards to be evaluated and controlled, but they do not provide much guidance on how to actually do it. NFPA 350 tells you how by providing supporting information on identifying hazards, performing gas monitoring, controlling hazards, and providing ventilation. The atmospheric monitoring chapter in NFPA 350 explains how to select the appropriate gas monitor, calibrate it, and interpret the results. Information on interferences and limits of detection are also provided, as are best practices for gas monitoring. The ventilation chapter explains the limits of natural ventilation in a confined space and explains how to select and configure ventilation equipment in a confined space. Information is provided on ventilation of inert atmospheres and bonding and grounding of flammable or combustible atmospheres; drawings of typical ventilation configurations are provided in an annex.

NFPA 350 recommends that all confined spaces are evaluated using a pre-entry evaluation form, a signed checklist used to identify and document hazards that are inherent, introduced, or adjacent to the space. NFPA 350 recommends atmospheric monitoring of all confined spaces regardless if an atmospheric hazard is anticipated. This additional step verifies the space is safe prior to entry, since atmospheric hazards continue to be a major source of confined space fatalities. This precaution to monitor all confined spaces prior to entry regardless of anticipated hazard goes beyond OSHA requirements, and assumes the confined space contains an atmospheric hazard until proven safe with the proper gas monitoring device.

Test results are recorded on the pre-entry evaluation. If no physical or atmospheric hazards are found, the pre-evaluation form is signed and no permit is needed. If, however, there are hazards that cannot be fully eliminated, a full permit issued by an entry supervisor is required prior to entry. This permit indicates the conditions under which entry may occur and establishes controls that must be used for entry.

Gaps identified in existing standards have also been addressed in NFPA 350. Throughout the document, NFPA 350 references hazards that are inherent, introduced, or adjacent to the confined space. While most confined space entry programs incorporate the evaluation of inherent and introduced hazards, few address adjacent hazards. There have been several incidents where fatalities were documented or suspected when an employee was exposed to a hazardous atmosphere adjacent to a confined space that caused the employee to fall into a confined space. NFPA 350 recommends signage for inerted tanks to alert employees of the hazard of such atmospheres adjacent to a confined space.

NFPA 350 also recognizes that demonstrated competencies are critical for workers involved in confined space entry and work. OSHA standards identify roles for confined space entry, but NFPA 350 provides specific recommended competencies for those who perform tasks such as gas monitoring, ventilation, and rescue. NFPA 350 also recognizes gaps in rescue provisions in existing regulations, and provides the organizational elements of emergency preparedness that are normally in place in a fire department but not necessarily in a facility rescue program. The rescue chapter includes information on pre-incident planning and evaluation, rescue gear, rescue configurations, and rescue competencies. The document works in conjunction with NFPA 1670, Operations and Training for Technical Search and Rescue Incidents, for technical aspects of confined space rescue.

Since many confined space incidents relate to change, a chapter on management of change (MOC) has been included in NFPA 350. The MOC system identifies and evaluates potential effects of modifications to confined space configurations, equipment, materials, content, and work tasks. A sample MOC form, provided in an annex, serves to document that the effects of change have been considered.

Finally, NFPA 350 provides a chapter on prevention through design (PtD) specifically for confined spaces. The PtD concept seeks to initiate a design process to reduce or eliminate inherent risks and hazards associated with the design of facilities, equipment, and products. The PtD process can minimize retrofitting control costs and the use of labor-intensive administrative hazard control measures. While the implementation of methods provided throughout NFPA 350 will improve confined space safety, the only way to fully prevent confined space incidents is to eliminate the confined space completely through design or redesign.

NANCY PEARCE is senior fire protection engineer at NFPA and chair of AIHA’s Confined Spaces Committee. Top Photograph: Getty Images