Space confined

The danger associated with working in confined spaces is not new. Since the discovery of mines, many fatalities have been reported owing to suffocation, gas poisoning, accumulated gas explosion, and asphyxiation. Workers dealing with wastewater sewage repair, cleaning, inspection. 

A space large enough for an employee to enter and work with restricted activities or movement may have a hazardous atmosphere. The incident occurs because of failure of recognizing the hazards associated with confined spaces. The different kinds of confined spaces for a worker in a plant are tanks, silos, storage bins, vessels, hoppers, pits, and sewer lines. Big fermenters, multieffective evaporators, boilers, and wells are also included in this list. 

There is another criterion called permit-required confined space such as an engvilfment, entrapment, or any other recognized serious safety or health hazards. 

Sometimes in a confined space the internal configuration or shape is built to have inwardly converging walls or a floor that slopes downward and tapers to a smaller cross section that could trap an entrant or contribute to asphyxiation. This is designed as a permit-required confined spaced. Examples are fermenter and digester. 

The space that contains any other recognizable serious safety or health hazards is also a permit-required confined space. These hazards may be physical, electrical, mechanical, chemical, biological, radiation, temperature extremes, and structural hazards. 

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Madsen C and Jacobsen C J FI 1999 Nanosized zeolite crystals—convenient control of crystal size distribution by confined space synthesis Chem. Commun. 673-4... 

Prolonged soldering in confined spaces with restricted air circulation requires ventilation. A small duct fan is recommended for hot-wire stripping. Tefzel articles should not be exposed to welding conditions. 

Formic acid is combustible (flash point = 69° C), but the explosive ha2ard is considered slight. The decomposition to CO requires appropriate precautions to be taken when entering tanks or other confined spaces that have contained the acid. 

The product is considered nonhazardous for international transport purposes. However, it is an oxidizing agent sensitive to decomposition by water, direct sources of heat, catalysts, etc. Decomposition is accompanied by the Hberation of oxygen and heat which can support combustion and cause pressure bursts in confined spaces. Decomposition in the presence of organic material is rapid and highly exothermic. 

Entry into Confined Spaces. In 1993 OSHA adopted a confined space entry rule (93) requiring employers to evaluate the workplace to (/) determine if it contains any confined spaces, (2) mark or identify such confined spaces, and (2) develop and implement a permit program for entry into such spaces. The program must include a permit system which specifies the steps to be taken to identify, evaluate, control, and monitor possible electrical, mechanical, and chemical ha2ards select and use equipment institute stand-by attendance and estabflsh communications. The reference standard (93) should be studied for details. 

Confined Space Enty Program, 29 CFR 1910.146, U.S. Department of Labor, Occupational Safety and Health Adrninistration, Jan. 14, 1993. 

Included ia the OSHA regulations are standards for safe work practices such as lock-out/tag-out and confined space entry, personal protective equipment, storage of hazardous materials, welding process, forklift operation, and requirements for fire protection. Basically, all activities within a chemical facihty are covered by OSHA standards. 

Because biphenyl is often transported in the molten state, a moderate fire ha2ard does exist under these circumstances. Biphenyl, with a flash point of 113°C, has a lower flammability limit of about 0.6% (by volume) at the flash point to an upper limit of 5.8% at 166°C (42). Dust explosions are a ha2ard when vapors from a hot Hquid surface condense in air in a confined space. 

The use of black cyanide as a fumigant and rodenticide makes use of the atmospheric humidity action that Hberates hydrogen cyanide gas. It can only be used effectively ia confined spaces where hydrogen cyanide builds up to lethal concentrations for the particular appHcation. Black cyanide is also used ia limited quantities ia the production of pmssiates or ferrocyanides (see Iron compounds). 

The success of compression agglomeration depends on the effective utilization and transmission ofthe applied external force and on the ability of the material to form and maintain interparticle bonds during pressure compaction (or consolidation) and decompression. Both these aspects are controlled in turn by the geometiy of the confined space, the nature of the apphed loads and the physical properties of the particulate material and of the confining walls. (See the section on Powder Mechanics and Powder Compaction.)... 

Jobs which raise special problems. Such jobs might include entry to vessels and other confined spaces, hot work, and responsibilities of contractors. 

Pressure Development Overpressure in a UVCE results from turbulence that promotes a sudden release of energy. Tests in the open without obstacles or confining structures do not produce damaging overpressure. Nevertheless, combustion in a vapor cloud within a partially confined space or around turbulence-producing obstacles may generate damaging overpressure. Also, turbulence in a jet release, such as may occur with compressed natural gas discharged from a ruptured pipehne, may result in blast pressure. 

Definition of Dust E losion A dust explosion is the rapid combustion of a dust cloud. In a confined or nearly confined space, the explosion is characterized by relatively rapid development of pressure with a flame propagation and the evolution of large quantities of heat and reaction products. The required oxygen for this combustion is mostly supphed oy the combustion air. The condition necessaiy for a dust explosion is a simultaneous presence of a dust cloud of proper concentration in air that will support combustion and a suitable ignition source. 

Dow Chemical Company Safety Standard on Confined-Space Entry states the following regarding confined space entiy. 

Material solidifies Monitor and control temperature in feed system or is too viscous, Heat trace and/or insulate lines and plugs lines. Potential for proper line break procedures exposure while Use personal protective equipment (PPE) correcting, proper lockout-tagout and confined space problem. entry procedures CCPS G-23 CCPS G-29 Fisher 1990... 

API Publ 2217A, Guidelines for Work in Inert Confined Spaces in the Petroleum Industry, 2nd ed., November 1997... 

Vapor Cloud Explosion (VCE) Explosive oxidation of a vapor cloud in a non-confined space (not in vessels, buildings, etc.). The flame speed may accelerate to high velocities and produce significant blast overpressure. Vapor cloud explosions in plant areas with dense equipment layouts may show acceleration in flame speed and intensification of blast. 

The second unusual feature is that it has frequently been observed that the rubbers soften or reverse when subjected to high temperatures in a confined space. This is believed to be due to the presence of trapped moisture which, when not able to escape, causes hydrolysis of the polymer. 

Operation in confined spaces Improper isolation From residues Oxygen deficiency (inherent, from purging or from rusting)... 

For entry into a confined space which may contain toxic chemicals or be oxygen deficient. Refer to Figure 13.1. 

The special precautions appropriate for entry into confined spaces are summarized in Chapter 13. In fires, evacuation of burning buildings, prohibition on re-entry and the use of self-contained breathing apparatus by fire-fighters are key precautions. 

Entry into a confined space requires strict control (page 417). Whenever oxygen deficiency may be encountered air quality checks should be made and appropriate breathing apparatus used. 

Enter any confined space, e.g. any tanks or pits, except in accordance with a permit-to-work system. 

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