Confined spaces

What is a confined space?

The definition is based on three characteristics that must be present: the space is large enough for a person to enter and perform work, it has limited or difficult means of access and egress, and it is not designed for continuous occupancy. In addition, there must be the possibility of a hazardous atmosphere due to oxygen deficiency or excess, the presence of toxic gases or vapors, or flammability, as well as other risks such as engulfment by bulk materials, flooding, entrapment by moving parts, electrocution, falls, and heat.

Accidents in confined spaces have two distinguishing characteristics: they are frequently fatal, and multiple people often die because those attempting to rescue the first victim enter without protection and suffer the same injuries. The hazardous atmosphere can be created by the enclosure’s existing contents (fermentation, decomposition, product residue), by the work being carried out (welding, painting, solvent cleaning), or by infiltration from the outside, and it can change during the rescue operation.

There is no specific regulation for confined spaces in Spanish law. The obligation arises from Law 31/1995 (assessment, planning, training, emergency measures), Royal Decree 486/1997 on workplace safety, Royal Decree 374/2001 on chemical agents, Royal Decree 681/2003 on explosive atmospheres, and the provisions on preventive resources, which consider work in confined spaces among the activities requiring their presence. The INSST (National Institute for Safety and Health at Work) has developed the technical criteria in NTP 223 and subsequent documents.

Main risks

• Oxygen deficiency. Due to consumption (oxidation, combustion, fermentation), displacement by other gases or absorption; below 19.5 percent oxygen is considered a deficient atmosphere, and loss of consciousness can be immediate at low concentrations.
• Toxic atmospheres. Hydrogen sulfide in sewers and pits, carbon monoxide from combustion, carbon dioxide from fermentation, solvent and cleaning product vapors, remnants of the previous contents.
• Flammable or explosive atmospheres. Fuel vapors, fermentation gases, combustible dusts; any source of ignition can cause an explosion.
• Oxygen enrichment. Due to leaks from oxy-fuel cutting equipment; increases the flammability of clothing and materials.
• Physical risks. Engulfment in silos, flooding in wells and collectors, entrapment by agitators or belts, falls in access areas, heat and humidity, amplified noise, electrocution in damp areas.

Work procedure

1. Identification and inventory of the center’s confined spaces, with signage and access control.
2. Specific evaluation of each intervention: previous content, tasks to be carried out, foreseeable atmosphere, means of access, communication and rescue.
3. Entry permit issued by an authorized person, which includes the conditions, measurements, measures and people involved, with a limited validity period.
4. Isolation and containment: closing and blocking of pipes, valves and electrical and mechanical feeds; draining, cleaning and purging.
5. Atmospheric measurement before entering and continuously during work, with a calibrated detector of oxygen, flammable gases and foreseeable toxic gases, measuring at different heights.
6. Forced ventilation before and during the intervention; ventilation does not replace measurement.
7. Permanent external surveillance by a trained person who does not enter under any circumstances, maintains communication and activates the rescue.
8. Equipment: harness with rescue line and tripod or equivalent device, suitable respiratory protection (atmosphere-supplying when the atmosphere is not breathable or is uncertain), lighting and explosion-proof tools where appropriate.
9. Proven rescue plan, using own resources or coordinated with emergency services; rescue without entering is always the first option.
10. Closure of the permit, removal of equipment and registration of the intervention.

Organizational application

• Written procedure. Approved by management, with definition of spaces, roles (authorizing person, entry person, standby attendant, rescuer), permit template and equipment.
• Specific training. Theoretical and practical for new entrants and standby attendants, including the use of detectors, respiratory protection and rescue techniques; periodic refresher training.
• Equipment. Calibrated and verified detectors, checked rescue equipment, respiratory protection appropriate to the risk and maintained.
• Contractors. Most interventions are carried out by external companies; the coordination of business activities must ensure that they know the premises, apply the procedure and have rescue resources.
• Preventive resource. Mandatory presence when the work is classified as being of special risk, with the ability to stop the intervention.

Limits and common mistakes

1. Entering without measuring, or measuring only at the beginning and not during the work, when the atmosphere can change in minutes.
2. Relying on ventilation or the absence of odor as an indicator of safety.
3. Attempting rescue by entering without respiratory protection: this is the cause of most multiple deaths.
4. Use filter masks in oxygen-deficient or unknown-composition atmospheres, where only insulating equipment provides protection.
5. Do not isolate the power supplies, as this could cause the room to fill up or moving parts to start up during the intervention.
6. Consider that a small, open or brief intervention area is not a confined space and omit the procedure.

The oxygen criterion of 19.5 percent and the reference values ​​for toxic and flammable gases must be taken from the updated technical documentation of the INSST and the current occupational exposure limits, and adapted to each intervention.

Regulatory framework and technical references in Spain

• Law 31/1995, articles 16, 20 and 32 bis . Evaluation and planning, emergency measures and presence of preventive resources.
• Royal Decree 39/1997, article 22 bis . Presence of preventive resources in activities of special risk, including work in confined spaces.
• Royal Decree 374/2001 . Evaluation and control of chemical agents, including hazardous atmospheres.
• Royal Decree 681/2003 . Protection against risks arising from explosive atmospheres in the workplace.
• NTP 223: Work in confined spaces (INSST) . Definition, risks and reference preventive measures.

In the United States, OSHA standard 29 CFR 1910.146 on permit-required confined spaces is a common international reference, but it is not applicable in Spain. In Colombia, Resolution 0491 of 2020 regulates work in confined spaces.