25-REHABILITATION OF THE EAST ELEVATED STORAGE TANK

Home Browse Search

SSPC-Guide 12 June 1, 1998 Editorial Revisions November 1, 2004 in case of abnormal operations of equipment, or (b) in which hazardous concentrations of gases or vapors are normally prevented by positive mechanical ventilation, and which might become hazardous through failure or abnormal operations of the ventilation equipment, or (c) that is adjacent to a Class I, Division 1 locations and to which hazardous concentrations of gases or vapors might occasionally be communicated unless such communica- tion is prevented by adequate positive pressure ventilation from asource ofclean air, and effective safeguards against ventilation failure are provided. Class tl locations: Class II locations are those that are hazardous because ofthe presence of combustible dust. Class II locations include the following: Class II, Division 1: AClass II, Division 1 location is a loca- tion: (a) in which combustible dust is or may be in suspen- sion in the air under normal operating conditions, in quanti- ties sufficient to produce explosive or ignitable mixtures; or (b) where mechanical failure or abnormal operation of machinery or equipment might cause such explosive or ignitable mixtures to be produced, and might also provide a source of ignition through simultaneous failure of electric equipment, operation of protection devices, or from other causes, or (c) in which combustible dusts of an electricaliy conductive nature may be present. Class II, Division 2: A Class II, Division 2 location is a location in which: (a) combustible dust will not normally be in suspension in the air in quantities sufficient to produce explosive or ignitable mixtures, and dust accumu- lations are normally insufficient to interfere with the normal operation of electrical equipment or other apparatus; or (b) dust may be in suspension in the air as a result of infrequent malfunctioning of handling or processing equipment, and dust accumulations may be ignitable by abnormal operation or failure of electrical equipment or other apparatus. Class III locations: Class III locations are those that are hazardous because of the presence of easily ignitable fibers or flyings (e.g., dust) but in which such fibers or flyings are not likely to be in suspension in the air in quantities sufficient to produce ignitable mixtures. Class III locations include the following: Class III, Division 1:ACIass III, Division 1 location is a loca- tion in which easily ignitable fibers or materials producing combustible flyings are handled, manufactured, or used. Class III, Division 2: A Class III, Division 2 location is a location in which easily ignitable fibers are stored or handled, except in process of manufacture. Note: The above definitions of hazardous (classified) loca- tions are taken directly from 29 CFR 1926.449. Refer to the OSHA standard for additional information and examples for each classification. Hazardous Atmosphere: An atmosphere that may expose employees to the risk of death, incapacitation, impair- ment of ability to self-rescue (that is, escape unaided from a permit space), injury, or acute illness from one or more of the following causes: (1) flammable gas, vapor, or mist in excess of 10 percent of its lower flammable limit (LFL); (2) airborne combustible dust at a concentration that meets or exceeds its LFL; (3) atmospheric oxygen concentration below 19.5% or above 23.5%; (4) atmospheric concentration of any substance for which a dose or a permissible exposure limit is published in subpart G, Occupational Health and Environmentai Control, or in subpart Z, Toxic and Hazardous Substances, which could result in employee exposure in excess of its dose or permis- sible exposure limit; (5) any other atmospheric condition that is immediately dangerous to life or health. NOTE: This definition is taken directly from 29 CFR 1910.146. For the purposes of this guide, onlythose considerations in selecting lighting dealing with the concentrations of flammable vapors or combustible dusts [items (1) and (2) above] are addressed. The reader is cautioned to consider all other aspects of a hazardous atmosphere as described above. lower Flammable Limit: The lower limit of flammability of a gas or vapor at ordinary ambient temperatures expressed in percent of the gas or vapor in air by volume. Lower Flammable Limit is synonymous with Lower Explosive Limit. A.3 EVALUATION OF WORK SITES: Before any aspect of an industrial painting project commences, the location must be evaluated to determine whether a hazardous atmosphere exists. This evaluation involves a thorough inspection of the work location and often includes both a visual inspection and monitoring for atmospheric hazards. OSHA's permit-required confined space standard (29 CFR 1910.146) requires that employers test and monitor spaces with instruments which detect all aspects of hazardous atmospheres that may be encountered. OSHA has classified atmospheric hazards into three categories: toxic; asphyxiating; and flam- mable or explosive atmospheres. Monitoring tests are typi- cally performed using a direct reading instrument which gives an instantaneous assessment of the degree of atmospheric hazard. From a lighting perspective, the minimum required tests in any suspect hazardous atmosphere include oxygen level, the concentration of flammable gases or vapors, and the concentra- tion of combustibie dust. A.4 SURVEY CONSIDERATIONS: Initial testing for hazards may not be enough. Periodic or continuous testing may be req uired, as conditions can change and become hazardous during the painting project. Conditions may also vary throughout a work space. Concentrations of flammable gases and vapors may vary depending on their physical characteristics (i.e., heavier gases may tend to concentrate near the bottom of tightly sealed spaces while light gases may concentrate near their emission source or near the top of the space). With this in mind, a monitoring strategy must be developed which takes into account both the physical properties of potential atmospheric hazards and the physical characteristics of the structure. The instrumentation 9-51 529