cofferdams and confined space

For cofferdams and confined space entry in construction and excavation work, the safest approach is to treat any cofferdam, excavation, shaft, vault, manhole, tank, sewer, or similar enclosed area as a potential permit-required confined space until a hazard assessment shows otherwise. Key hazards include oxygen deficiency or enrichment, flammable or explosive atmospheres, toxic gases and vapors, engulfment by water, soil, sludge, or flowing materials, and physical hazards such as mechanical equipment, electrical energy, heat, noise, entrapment, and restricted egress. In cofferdams specifically, also evaluate flooding, seepage, instability, adjacent utility releases, vehicle exhaust, welding fumes, and changing atmospheric conditions caused by pumps, coatings, cutting, or hot work. [5] [15] [13]

Atmospheric testing must be completed before entry and repeated as needed during the job. Test from top to bottom because gases stratify, and monitor at least oxygen, combustibility/LFL, and expected toxic contaminants such as hydrogen sulfide or carbon monoxide. Testing should be performed by a trained, competent person using a direct-reading gas monitor that is calibrated and function-checked. Record the results, keep them at the job site, and make them available to affected workers. If conditions can change, if hot work is performed, or if the work itself may affect air quality, continuous monitoring is the preferred practice. [5] [4] [10]

Acceptable entry conditions for atmosphere should include oxygen between 19.5% and 23.5%, flammable gas below 10% of the lower explosive limit, and toxic contaminants below applicable exposure limits. If testing shows unsafe conditions, do not enter until hazards are eliminated or controlled under a permit system with appropriate respiratory protection and rescue capability. Workers must leave immediately if monitor alarms activate or conditions deteriorate. [1] [7] [8]

Ventilation is a control measure, not a substitute for hazard evaluation. Purge, drain, flush, or pump out water, sediment, sludge, or contaminants before entry where necessary. Use mechanical ventilation with 100% outside air where applicable, open additional access points when feasible to improve circulation, and retest after a suitable ventilation period. In cofferdams and excavations, ventilation should also address diesel exhaust, welding fumes, solvent vapors, and stagnant low-lying air. If ventilation alone cannot maintain safe conditions, entry should proceed only under permit-required procedures with additional controls such as supplied-air respiratory protection. [1] [2] [6]

A permit-required confined space program is required when the space has actual or potential atmospheric hazards, engulfment hazards, or other serious safety hazards. All spaces should be treated as permit-required until pre-entry procedures demonstrate otherwise. The permit should identify the space, purpose of entry, authorized entrants, attendant, supervisor, emergency contacts, hazards, isolation steps, atmospheric test results, PPE, communication method, rescue arrangements, and permit duration. A new permit or re-evaluation is needed if work is interrupted or conditions change. [2] [14] [2]

• Isolate all hazardous energy before entry: lockout/tagout equipment, de-energize circuits, blank or cap lines, and isolate pumps, piping, sewers, and other sources that could introduce material or energy into the space.
• Survey the surrounding area for drifting vapors, sewer gases, adjacent process releases, vehicle exhaust, water intrusion, and excavation-related hazards.
• Provide at least one attendant outside the space whenever permit entry is required, maintain constant communication, and prevent unauthorized entry.
• Use appropriate PPE based on the hazards: hard hat, gloves, eye protection, protective clothing, hearing protection, fall protection, respiratory protection, and intrinsically safe or explosion-proof lighting and tools where needed.
• Post the permit at the entry point and secure the area around the opening or excavation.

[5] [8] [1] Rescue planning is critical because many confined-space fatalities occur during impulsive rescue attempts. At least one attendant should remain outside to summon help and monitor entrants. The attendant must not enter for rescue until additional help arrives and only if trained, equipped, and authorized. Non-entry rescue is preferred whenever feasible, using a full-body harness, lifeline, and mechanical retrieval device such as a tripod or block and tackle. Rescue personnel should be trained in first aid and CPR, and the rescue plan should be specific to the space, hazards, access limitations, and retrieval method. [1] [1] [9]

Worker training must cover confined-space hazard recognition, permit procedures, atmospheric testing, monitor use and alarm response, ventilation, isolation/lockout, communication, attendant duties, PPE, rescue procedures, and emergency response. Only trained and authorized employees should test, supervise, attend, or enter permit spaces. Training should be refreshed whenever duties change, equipment changes, or deficiencies are observed. For cofferdam and excavation work, training should also address water hazards, engulfment, fall hazards, access/egress, mobile equipment, and changing site conditions. [2] [3] [9]

For emergency response, establish a written plan before entry. The plan should identify who to call, how entrants and attendants communicate, how alarms are triggered, what rescue equipment is staged, whether rescue is non-entry or entry, and how EMS/fire rescue will access the site. Stop work and evacuate immediately if there is an alarm, loss of ventilation, flooding, engulfment risk, fire, collapse, medical emergency, or any unplanned change in conditions. In construction and excavation operations, coordinate the confined-space plan with excavation protection, dewatering, traffic control, utility control, and site emergency procedures. [14] [14] [3]

Relevant OSHA requirements include 29 CFR 1910.146 for permit-required confined spaces in general industry, which is commonly used as the baseline for hazard evaluation, permits, testing, attendants, and rescue. For construction activities, employers should also apply OSHA's confined spaces in construction rule, along with excavation requirements in 29 CFR 1926 Subpart P and cofferdam requirements in 29 CFR 1926 Subpart S where applicable. In practice, cofferdams used in construction often involve both excavation and confined-space hazards, so employers should integrate both sets of controls rather than treating them separately. [5] [9] [9]

• Classify the space before entry and assume permit-required status until proven otherwise.
• Complete a site-specific hazard assessment for atmospheric, engulfment, electrical, mechanical, thermal, and access hazards.
• Isolate energy and material sources; lock out, blank, block, drain, purge, and dewater as needed.
• Test the atmosphere before entry, after ventilation, and continuously or periodically based on risk.
• Ventilate with outside air and stop entry if safe conditions cannot be maintained.
• Use an entry permit, attendant, communication system, and trained authorized entrants.
• Stage rescue equipment before entry and prohibit unplanned entrant-to-entrant rescue.
• Maintain safe access/egress, fall protection around openings, housekeeping, lighting, and traffic control.
• For excavation and cofferdam work, inspect for water intrusion, soil movement, structural instability, and adjacent operations that could affect the space.
• Suspend work during storms, flooding, pump failure, monitor alarms, or any change that invalidates the permit.

[2] [11] [12]