Acquisition Safety -- Confined Spaces |
Introduction | Discussion | Recommendations | Conclusion | Resources |
Introduction |
Confined spaces are compartments or enclosures that have limited openings for entry and exit, are not intended for continuous human occupancy, and are only suitable for temporary work such as inspections, maintenance, or repairs. These spaces may be oxygen deficient, contain fire, explosion or toxicity hazards, or hold liquid, sludge, or solids that create potential engulfment and/or drowning hazards. There are many such confined spaces aboard ship such as cargo holds, tanks, pump rooms, cofferdams, and duct keels. Entering these confined spaces without proper procedures and precautions could cause fires, explosions, bodily injury, illness, or death. Proper planning in ship design to minimize or eliminate the need for confined space entry can save lives and life cycle costs. |
Discussion |
Confined spaces create serious potential hazards that must be addressed during ship construction, use, repair and overhaul, and ship salvage and dismantlement. Working in confined spaces during each of these different ship life cycle phases presents challenges that require planning and management of these spaces. Confined spaces are typically difficult to enter and exit, especially in an emergency. They may also contain hazardous atmospheres and other safety hazards as described below that could cause serious physical injury or death. General safety hazards in confined spaces include communication problems, entry and exit limitations, fall hazards, physical and mechanical hazards, etc. The U. S. Navy requires that its ships, aircraft, and shore facilities control their confined spaces by requiring special precautions, including training of personnel who work in and monitor these spaces and testing and approval by a certified gas free technician or marine chemist, before authorizing any person or persons to enter a confined space. Because of the special nature of confined spaces found aboard Navy ships, this section of the Acquisition Safety website will concentrate on the challenges of entering and working in shipboard confined spaces and the importance of planning in the ship design phase to minimize or eliminate the need for confined space entry. Hazardous AtmospheresThe internal atmospheres of confined spaces may be oxygen deficient, flammable or explosive, toxic, or oxygen enriched, which may result in the risk of suffocation, fire and explosion or impaired physical capability for persons entering these spaces. A hazardous atmosphere is defined by its potential to disable and/or injure those exposed. It may be characterized by how much it differs from the normal air we breathe. Normal air is defined as approximately 21 percent oxygen, 73 percent nitrogen, a trace of carbon dioxide and a very small trace of other gases such as argon. If levels of these constituents change, whether up or down in concentration, then the atmosphere is considered hazardous. Asphyxiating Atmospheres: Oxygen deficiency may be caused by oxidation reactions such as fire or rusting. It also can take place during combustion of flammable substances, as in welding, heating, cutting, and brazing. Other causes for oxygen deficiency include the dilution of air with an inert gas (e.g., nitrogen or argon) and absorption by grains, chemicals, or soils. Normal air contains 20.9% oxygen; once the level drops below 19.5%, the air becomes hazardous to breathe. As the level of oxygen is decreased in a space, the danger of asphyxiation for anyone entering that space increases. Oxygen deficiency provides minimal sensory warning. Symptoms may include ringing in the ears, dizziness and often-impaired cognitive functions. The victim may initially feel giddy and be otherwise impaired in his ability to sense the onset of problems. Toxic Atmospheres: Toxic gases and vapors come from evaporation of fuel and solvents, or may be formed in the process of fermentation and during decomposition of both animal and vegetable material. Welding or brazing with metals such as mild steel, high strength and stainless steel produces toxic metal fumes and hazardous gaseous byproducts; recirculation of diesel exhaust emissions (used to suppress fuel tank atmospheres) will create a toxic atmosphere; and collection and holding tanks (CHTs) for sewage (blackwater) generate hydrogen sulfide, methane, and other hazardous byproducts in the tanks, piping, and valves. Flammable and Explosive Atmospheres: This condition generally arises from vaporization of flammable liquids (fuels or solvents), byproducts of work such as spray painting and welding, chemical reactions, concentrations of combustible dusts, and desorption of chemicals from inner surfaces (bulkheads and decks) of the confined space. Welding or other hot work may liberate flammable vapors from combustible liquids previously stored in a compartment. Gas free procedures must evaluate not only the present material stored in an area, but must also consider previous cargoes and contents of adjacent spaces. Other Common Shipboard Confined Space ChallengesCommunication Problems: If a worker in a confined space should suddenly feel distressed and is not be able to summon help, an injury could become a fatality. Frequently, the body positions that are assumed in a confined space make it difficult for the standby person to detect an unconscious worker. Visual monitoring of the worker is often not possible because of the design of the confined space or location of the entry hatch. Effective process management and supporting OSHA regulations (29 CFR Part 1915 Subpart B -- Confined and Enclosed Spaces) require provision for communication between worker and monitor and the means for emergency rescue, which must be identified before confined space entry. Entry and Exit Limitation: The time it takes to enter and exit confined spaces may increase the hazards of exposure to the confined space atmosphere. Other Physical Hazards: While working in a confined space, workers can become fatigued or be exposed to extreme heat and cold, hazardous noise levels, vibration, or radiation. Drowning hazards include engulfment in sludge and other liquids. Additional physical hazards include inadvertent contact with electrical, rotating, or mechanical equipment, steam or other sources of burning heat, and moving parts. Monitoring and Display of Fluid Levels Inside Tanks: Some Navy ships have more than 150 tanks onboard that carry millions of gallons of diesel fuel, aviation fuel, potable water, feed water, oily waste, sewage (blackwater), etc. Other tanks are used for ballasting and list control. Traditionally, tanks installed onboard Navy ships used float type tank level indicators to monitor and display fluid levels in the tanks. These indicators consisted of a series of floats that were wired together inside of the tanks. The floats contained many internal electronic components to determine the tank fluid level. Whenever the floats needed maintenance, the tanks would have to be drained, opened, and freed of harmful gases before workers could enter them (see the Recommendations section for new Navy methodology). Monitoring Tanks for Corrosion Inspection and Maintenance: Monitoring tanks aboard ships for corrosion maintenance is a very costly confined space problem. Tanks are difficult to inspect and evaluate. More than 4,000 shipboard tanks are opened, cleaned, and inspected each year at a cost of $32 million. Fifty percent of tank work is unplanned due to the inability to monitor tank conditions between inspections, which means that corrosion or other problems may create a repair need during the interval between cyclic inspections. Fall Prevention for Entering and Working in Confined Spaces: Confined spaces also present the risk of slips, trips, and falls, especially where corrosion has caused rust, which damages ladders, walking surfaces, and anchor points for personal fall arrest systems. Many tanks have no proper fall protection equipment, anchors, or ladders inside. Shipboard tanks can be as deep as 60 feet requiring scaffolding to be set up to perform maintenance. Scaffolding can present another fall hazard.
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Recommendations |
The first goal of new ship design should be to eliminate the need to enter confined spaces for maintenance, repairs, or other purposes. Where confined space entry is unavoidable, it is best to minimize the hazards involved in working in a confined space at the ship design stage and during the initial installation of ship equipment. Provide Remote Monitoring and Inspection SystemsRemote monitor/inspection systems and automated cleaning systems eliminate or minimize the need for confined space entry. For example, the Navy is replacing float type tank level indicators with non-intrusive radar (radio detection and ranging) tank level indicators. The radar indicators are mounted externally to the tank. The radar indicator sends a pulse down the tank that is reflected off the fluid level; and the indicator measures the time it takes for the signal to return. The shorter the return time, the higher the fluid level is inside the tank. This signal is then converted into depth in inches to determine tank height. Existing sounding tables can be used to convert the reading from inches into gallons.
Provide Access for Inspection (if remote sensing/monitoring is not available or entry is required)Not all spaces and tanks will have remote sensing/monitoring, and for these spaces or tanks safe access must be provided. Condition based maintenance may require more frequent inspections. Designers should provide for ventilation, isolation of supply and drain lines, control of hazardous energy, ladders, anchorage, and walkways where possible. For example, the design of complex CHT tanks' aeration systems should anticipate the need for worker entry and occupancy. (see the McManus reference in the Resources section, which contains an excellent check list for confined space design concerns). Use Materials that Reduce the Need for MaintenanceDesigning and selecting equipment should be done on the basis of reducing, even eliminating, worker exposure in confined spaces. Coating systems should be used that have longer service lives so workers do not need to enter confined spaces often. For example, the Navy has used improved commercial off-the-shelf mechanical seals for pump applications that last longer and are easier to install and maintain.
Provide Adequate VentilationVentilation is one of the most effective means of controlling hazardous atmospheres in confined spaces. Providing adequate ventilation in confined spaces avoids build-up of contaminants or combustible atmospheres. Consider designs that will facilitate ventilation of the space. Ventilation modeling, including finite element analysis, may support designs and configurations that reduce purging time, minimize "dead spots" and facilitate more rapid availability. Factors to consider:
See the Ventilation section of this Acquisition Safety website for more information. Prevent Invasion of Contaminants to Confined Spaces
Design Adequate Means of Entry and ExitDesign adequate and convenient means of entry and exit for persons who may be required to wear personal protective equipment, a breathing apparatus, and protective clothing. A good example is to have a "butterworth opening" or separate entry hole for all support equipment so personnel are not required to enter through this same access point. Designers should recognize the need for two hatches for spaces into which workers must enter along with the "butterworth hole" for ventilation. Ventilation ducts or hoses should not impede personnel access or exit through hatches. To avoid costly retrofits, include "butterworth" hole and additional hatch designs before loading is calculated and the overall design structure is frozen. The same is true for design of lightening holes in tank baffles and girders. These should be positioned so workers can move from section to section of the tank without undue climbing. Provide Fall Hazard ProtectionTo prevent fall hazards in confined spaces, provide fixed ladders, platforms, guardrails, and anchor points for personal fall arrest systems. Puget Sound Naval Shipyard developed a device that can be inserted into D-holes - cut-outs in transverse bulkheads (metal separations inside shipboard tanks) - designed to accommodate a safety boot for climbing. These devices provide a certified anchor point for attachment of scaffolding or anchorages for personal fall arrest systems. Plan for Emergency RescueConfined spaces that will be entered by ship's crew and shipyard workers should be configured for the removal of injured or unconscious personnel. This means that hatches and trunks should be able to handle various stretchers (Stokes baskets, Oregon spine splint, Reeves sleeve or stretcher) and be configured to accommodate high angle rescue. Pad eyes and anchor points should be available for high angle rescue and hoisting stretchers. Adequate hoisting points should also be provided for movement of materials and equipment. Consider Other Design Modifications
Make Improvements in Personal Protective EquipmentIn situations where Navy or contractor personnel find it necessary to enter a confined space, proper personal protective equipment must be used. In the past few years, Navy ships have been equipped with excellent gas-detection equipment, such as the Ultra 4 gas analyzer. They also have excellent breathing devices, such as the supplied-air respirator, with a backup self-contained breathing apparatus (SCBA). For ventilating confined spaces, Navy ships typically use a fire main, pressure-driven exhaust fan, with elephant trunks. Protective clothing, such as chemically resistant coveralls and rubber gloves, can protect personnel entering confined spaces from developing occupational dermatitis or from absorbing toxic hazards (such as fuels) through their skin. |
Conclusion |
Design accommodations made for safe crew and worker confined space entry, inspection, and repair are relatively inexpensive compared to the costs of retrofits, destruction of equipment and property from fires or explosions, and tragic loss of personnel. |
Resources/Best Practices |
Confined Spaces Resources/Best Practices
DoD/Navy Instructions and Regulatory Requirements:ASTM F-1166-07 ASTM F-1337-91 DoD Instruction 5000.02 MIL-HDBK-46855A NOT 1 Mil Std 1472F OPNAVINST 5100.19 Series Confined Space Design Guidance Documents:Guidance Notes for the Application of Ergonomics to Marine Systems American Bureau of Shipping Confined Space Regulations:29 CFR Part 1915 Subpart B Confined Space Standards:ANSI Z117.1-2003, Safety Requirements for Confined Spaces - This revised standard provides minimum safety requirements to be followed while entering, exiting, and working in confined spaces at normal atmospheric pressure. Available from American Society of Safety Engineers . General Confined Space References:Complete Confined Spaces Handbook, John F. Rekus, copyright 1994, Lewis Publishers - This book provides plant managers, supervisors, safety professionals, and industrial hygienists with recommended procedures and guidance for safe entry into confined spaces. Confined or Enclosed Spaces and Other Dangerous Atmospheres Confined Space Entry, An AIHA Protocol Guide. 2nd Ed., AIHA Press 2001 Confined Space Safe Practice Rec. No 72 Human Factors Conference, London, 27 – 29 September 2000, Royal Institution of Naval Architects - Human factors in ship design and operation provides an opportunity to reduce cost, improve safety, increase effectiveness and improve conditions on board ships. Details of papers presented at this conference are available at http://www.rina.org.uk/ International Maritime Organization (IMO) Navy Shipboard Corrosion Maintenance Navy Shipboard Corrosion Maintenance Naval Safety Center Website Presentation NFPA 301 Code for Safety to Life from Fire on Merchant Vessels 2001 Edition NFPA 306 Control of Gas Hazards on Vessels 2001 Edition - guidelines for Marine Chemists and hazards of Confined and Enclosed Spaces aboard ships. NIOSH/NSRP Project Remote Tank Monitoring and Inspection Methods Safety and Health in Confined Spaces, Neil McManus, copyright 1999 Lewis Publishers - comprehensive review of all aspects of confined space entry including hazard assessment, Standards Guidelines, and protective measures. |
How to Contribute |
We need input from the Defense Acquisition community to address each of the ten Acquisition Safety challenges that are the subject of this website. Grow with us as we share information on how to meet the above challenges through the Defense Acquisition Process. Through the exchange of ideas, information resources, and improvements in methodology and design, these challenges can and will be met. To submit general information or information on Best Practices, or to submit a success story, please send an email to safe-webmaster@navy.mil with the subject line "Acquisition Safety." |
Last Modified: Friday, August 21, 2009