Ladders stepladder

Falls from ladder, stepladder Objects dropped by ladder user... 

Persons being struck by falling objects, including ladder/stepladder... 

As described for the corresponding polymers, a powerful strategy for arriving at soluble oligomers with maximum conjugative interaction is incorporation of the PPP backbone into a stepladder - or ladder (see Sect. 2.2.) - framework, in... 

The logical continuation of the stepladder strategy outlined above for minimizing the mutual distorsion of adjacent main chain phenylene units was the incorporation of the complete PPP-parent chromophore into the network of a completely planar ladder polymer. The complete flattening of the conjugated 7T-system by bridging of all the subunits should then lead to maximum conjuga-tive interaction. As with the PTHP 11 systems, alkyl or alkoxy side chains should lead to solubilization of the polymers. 

Different conformations of base-paired DNA (a) the untwisted straight ladder, (b) the normal spiral ladder. The stepladder structure is unstable it can be converted into a spiral ladder by a right-handed twist, a change that permits the planes of the base pairs to come into close contact. 

A structural compromise between the fully bridged ladder system and the parent polyphenylene are stepladder polyphenylenes in which repeat units, such as fluorene, indenofluorene, or tetrahydropy-... 

Polyfluorenes are sometimes referred to as stepladder poly(przra-phenylene) (PPP) polymers as they have a backbone with a planar, ladder-like structure. The first poly-fluorene LED was made by Yoshino and coworkers using poly(9,9-dihexylfluorene) 16 [50]. 

Ladder polymers are also produced by polycondensation reactions of tetrafunctional monomers. If a tetrafunctional monomer is reacted with a bifunctional monomer, as in the formation of polyimides, the derived polymer is referred to as a partial ladder or stepladder polymer. 

PFs, PlFs, and poly(ladder-type pentaphenylene)s have methine bridges, and so are structurally related to LPPP 3. Stepladder polymers have also been prepared with other types of bridges. 

As shown in this review, the properties of polyphenylene-based materials, so as to maximise their potential as active materials in LEDs or polymer lasers, can be controlled by dehberate synthetic design. By incorporating bridges between some or all of the phenylene units to make ladder or stepladder polymers the effective conjugation length of the polymer may be controlled, while the interactions between the chains and the injection of charges may be regulated by careful selection of substituents. By these means it is possible to minimise interchain interactions, which lead to loss of luminescence... 

The term ladder is generally taken to include stepladders and trestles. The use of ladders for working above ground level is only acceptable for access and work of short duration (Work at Height Regulations 2005). 

Stepladder step- la-d9r (1751) n. A ladder having flat steps, or trends, in place of rungs usually provided with a supporting frame to steady it. 

A stepladder depends on spreaders and cross-bracing to keep the legs of the ladder in position relative to one... 

Never use a self-supporting ladder (such as a stepladder) as a single ladder or in a partially closed position. 

Step on the top two steps of a stepladder or the top three ladder rungs of an extension ladder. 

BE LADDER WISE Safety Guidelines for Stepladders INSPECT... 

Ladders must not be tied or fastened together to create longer sections unless they are specifically designed for such use. A metal spreader or locking device must be provided on each stepladder to hold the front and back sections in an open position when the ladder is being used. Two or more separate ladders used to reach an elevated work area must be offset with a platform or landing between the ladders, except when portable ladders are used to gain access to fixed ladders. 

The use of ladders and stepladders are not banned under health and safety law. The law says that ladders can be used for work at height when a risk assessment has shown that using equipment offering a higher level of fall protection is not justified because of the low risk and short... 

The employer needs to make sure that any ladder or stepladder is both suitable for the work task and is in a safe condition before use. Only use ladders or stepladders that ... 

In general, the types of polymers which have the best thermal properties are aromatic in character (often with recurring heterocyclic units), have low hydrogen content, and often have stepladder or ladder structures. Although there are numerous articles in the literature which deal with the effects of structure on stability within a given class of heat-resistant polymers, only a limited number of publications are to be found which compare the stabilities of different classes of heat-resistant polymers under controlled conditions. From Ehler s TGA studies on different classes of heat-resistant polymers, as well as from other sources, a classification can be made of the effects of structure on heat stability for several classes of compounds. For... 

A metal spreader or locking device shall be provided on each stepladder to hold the front and back sections in an open position when the ladder is being used. 

Cross-bracing on the rear section of stepladders shall not be used for climbing unless the ladders are designed and provided with steps for climbing on both front and rear sections. 

Furthermore, 1926.1053(a)(2) states Ladder rungs, cleats, and steps shall be. .. level... when the ladder is in position for use. Stepladders are typically designed so that the rungs are level when the ladder is in the open and locked position and the ladder is placed on a stable and level surface. Consequently, it is likely that positioning a stepiadder for use as a non-self-supporling ladder would result in the ladder s rungs being out-of-level, which would violate 1926.1053(a)(2). 

Stepladders, trestles and staging Many of the points above for ladders apply to step-ladders and trestles where stability and over-reaching are the main hazards. Neither of these should be used as a workplace above about 2 m in height unless proper edge protection is provided. 

Safe use of ladders and stepladders An employer s guide, INDG402, 2005, HSE Books ISBN 0 7176 6105 9... 

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