Protection Techniques

In addition to selecting the appropriate solvent system, pH, buffer species and then concentration, ionic strength, dielectric constant, type of container, and storage temperature, the following techniques may be used to enhance the photostability of photolabile drugs. 

Fhoton absorbers are considered photostabilizers by virtue of their ability to preferentially absorb the incident energy responsible for photodecomposition. 

Various UV absorbers have been used to protect photolabile solutions of drugs. p-Aminobenzoic acid absorbs UV radiation in the 360 to 313 nm UV region. Evidence of its photoprotective ability has been reported for solutions of colchicine (70), tetracycline hydrochloride (71), doxorubicin hydrochloride (77), and reserpine (106). 

Other benzoic acid derivatives also function as effective photoprotective agents. Methylparaben has a photostabilizing effect on solutions of riboflavin (69). Ethyl aminobenzoate significantly enhanced the photostability of menadione in aqueous solutions (107). 

Urocanic acid is considered one of the major absorbers of UV radiation in the epidermis with a at 278 nm at pH 7 (110) and therefore functions as a natural sunscreen (111). Habib and Asker (77) found that urocanic acid significantly enhanced the photostability of doxorubicin hydrochloride solutions. 

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Explosion prevention by inerting has several advantages over explosion protection techniques, such as explosion venting. For example, with successful inerting, fires or business interruptions cannot occur. Nevertheless, beware of the potential of asphyxiation with inerting proper vessel entry procedures must be implemented and occasionally it may be prudent to monitor for oxygen in workplaces. 

Ignition Sources Normally it is best practice not to base explosion safety solely on the presumed absence of an ignition source. Explosion control should be based on prevention or protection techniques, or both. Even so, all reasonable measures should be taken to eliminate ignition sources. 

Thomas, G. O. 1998. Explosion Arrester Testing State of the Draft European Standard. Paper presented at the 3rd Worldwide Seminar on Explosion Phenomena and Application of Explosion Protection Techniques m Practice, February 8-12, 1998, Europex, Ghent, Belgium. 

Explosionproof Apparatus. The protection technique shall be permitted for equipment in those Class I, Division 1 and 2 locations for which it is approved. 

Oil Immersion. This protection technique shall be permitted for current-interrupting contacts in Class I, Division 2 locations as described in Section 501-6(b) (1) (2). 

T Wohr, F Wahl, A Nefzi, B Rodwedder, T Sato, X Sun, M Mutter. Pseudo-prolines as a solubilizing, structure-disrupting protection technique in peptide synthesis. JAm Chem Soc 118, 9218, 1996. 

The use of oxime bond formation with orthogonal protection techniques allows the efficient construction of an antiparallel four-helix-bundle TASP122 (Scheme 19) by condensing amphiphilic peptide blocks, containing aldehyde functions at the C- or N-terminus, to a topological template functionalized with selectively addressable aminooxy acetic acid moieties, t20,22,971... 

Fig. 4. Changes in A, GS mRNAs and B, GS isoenzymes, during nodule development. The abundances of the mRNAs were measured by an RNase protection technique and the isoenzymes following separation by IEX-HPLC (adapted from Cullimore et al., 1990). GSs=GS synthetase activity. The isoenzymes are as defined in Fig. 3.

Our evaluations using 2,4,5-T and 2,4-D have been conducted over the past 5 years in forests in Arkansas, Oregon and Washington. Objectives were to measure external exposure and internal doseage as determined by the total amount of the herbicide excreted in the urine and also to develop the best possible techniques for assessing exposure and dose absorbed. Exposure levels were related to job responsibilities and to protective techniques designed to limit exposure. 

Acceptable protection techniques for electrical and electronic valve accessories used in specific class and division locations include explosion-proof enclosures intrinsically safe circuits nonincendive circuits, equipment, and components dust-ignition-proof enclosures dusttight enclosures purged and pressurized enclosures oil immersion for current-interrupting contacts and hermetically sealed equipment. Details of these techniques can be found in the National Electrical Code Handbook, available from the National Fire Protection Association. 

The term intrinsic has a meaning similar to that of inherent, but the common usage of intrinsic in the chemical industry usually means a protection technique related to electricity. Intrinsic safety is based on the restriction of electrical energy to a level below which sparking or heating effects cannot ignite an explosive atmosphere (Lees,2 p. 513). 

For electrical apparatus outside of this scope, e.g. switchgear, IEC 60079-15 defines a protection technique restricted breathing enclosure. ... 

A certain disadvantage of this protection technique is the fact that the enclosure (and its components inside) shall be cleaned generally before the apparatus is energized, in order to remove any deposits of combustible dust inside, either following failure of pressurization or following normal shutdown. 

Special protection comprises all protection techniques such as powder filling, static pressurization and encapsulation (by plastics materials). At that time, these techniques started their career in the field of explosion protection and advanced to autonomous types of protection described by IEC or European Standards individually. VDE 0170/0171/1969-01 does not contain any specific requirements for these techniques. It has been the decision of the certifying body that an s -apparatus will operate at the same level of safety compared with other well-defined types of protection, e.g. flameproof enclosure d ... 

Pressurization, with its great diversity of apparatus to be explosion protected for zone 1 (and zone 2) applications, is the favoured protection technique for... 

The marking of such s -apparatus has been (Sch)s for mining equipment and (Ex)s G... for explosion protected apparatus (suitable for zone 1 applications). In many cases, protection techniques, which are covered by their own standards today, e.g. encapsulation - m - or static pressurization (as a part of pressurization - p - ), have entered the field of explosion protection as s -apparatus [17]. 

Table 7.2 Pressurization - p - according to EN 50016/2nd edition and IEC 60079-2/4th edition. Conditions of release and appropriate protection techniques...

Protection technique No release Limited release Unlimited release... 

Thermodynamic instability of flammable substances, e.g. an UEL exceeding 80% (v/v), does not allow the use of this protection technique. In this case, continuous dilution with air is required... 

Table 7.2 indicates that a release of combustible substances out of the containment system can be handled in a safe way, even in the case of an undefined flow of protective gas using leakage compensation and continuous flow of protective gas as protective techniques. 

In zone 2, the pressurization technique presents the greatest allowable bandwidth in selecting the electrical components to be installed inside an explosion protected enclosure in comparison with other types of explosion protection techniques as stated in IEC 60079-15, EN 50021 or VDE 0165. As a special feature, pressurization enables intervention and access of personnel... 

The advantage of pressurization - compared with other protection techniques, e.g. restricted breathing enclosure - is given by a positive pressure differential permanently maintained in the apparatus interior. Load cycles of the p-apparatus do not affect this pressure differential, and by this way, a cooling-down period caused by reduced or no-load conditions cannot cause an inverted pressure differential (the pressure of the surrounding atmosphere is somewhat higher compared with that in the apparatus interior) which may force the backstream of environmental flammable atmosphere into the interior of an apparatus. Pressurization guarantees safe operational conditions completely independent of load cycles. 

In the history of the development of explosion protection techniques for electrical apparatus located in zone 2, the non-sparking concept (see Section 2.4)... 

In more recent times, the n-concept has been extended to applications in the field of process control. In Table 11.2, a comparison is given between two CPU and power modules for remote I/O systems, one intended for zone 1 installation, the second for zone 2 application. Obviously, the zone 2 concept with a special protection technique offers some financial and technical benefits compared with a zone 1 apparatus which may be used in zone 2 as a matter of course. 

The inspiration for this book was a series of courses on Explosion Protection given in chemical plants and the enthusiastic response to these courses, as well as the progress made in protection techniques, for example in pressurization, in more recent times. 

This book is intended for engineers, scientists, plant safety personnel and for students in the field of electrical engineering to give an introduction to the basic principles of explosion protection and the relevant protection techniques. 

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