Lifting safety

As normally designed, vapor flow through a typical high-lift safety reliefs valve is characterized by limiting sonic velocity and critical flow pressure conditions at the orifice (nozzle throat), and for a given orifice size and gas composition, mass flow is directly proportional to the absolute upstream pressure. 

Fig. 12 Cutaway view of a high-lift safety valve. (Reproduced by kind permission of Delta Fluid Products Ltd.)...

The best known type of safety valve is the spring loaded safety valve. Figure 7.1 shows a high performance full lift safety valve [2],... 

Another example of the application of limit switches is in lift safety circuits. These employ hardwired components connected together in series in such a way that they must all be closed before the lift can operate, as shown in Fig. 13.8. If any one of the components were to become open circuit, the safety circuit would cause the main up or down contactors to open and the lift to stop. The ultimate top and bottom switches in the lift shaft are limit switches, which have contacts that open if the lift overshoots by a predetermined distance the top or bottom floors. 

Fig. 13.8 Lift safety circuit, incorporating roller lever switches for upper and lower ultimate limit switches.

Reporting of accidents and incidents Emergency preparedness Cranes and lifting safety... 

Certain types of equipment are specifically excluded from the scope of the directive. It is self-evident that equipment which is already regulated at Union level with respect to the pressure risk by other directives had to be excluded. That is the case with simple pressure vessels, transportable pressure equipment, aerosols and motor vehicles. Other equipment, such as carbonated drink containers or radiators and piping for hot water systems are excluded from the scope because of the limited risk involved. Also excluded are products which are subject to a minor pressure risk which are covered by the directives on machinery, lifts, low voltage, medical devices, gas appliances and on explosive atmospheres. A further and last group of exclusions refers to equipment which presents a significant pressure risk, but for which neither the free circulation aspect nor the safety aspect necessitated their inclusion. 

Exceptions to the preceding requirements would apply where explosionproof equipment is needed building ceiling heights are such that the standard 3.7-m (12-ft) lift is all that wih ever be needed and loads will never exceed 1 to 1.5 tons. Safety requirements for lift trucks are mandated by OSHA, by NIOSH (National Institute of Occupational Safety and Health), by State Depts. of Labor, and often by individual company standards. Among these requirements are backup-movement signals, seat belts, overhead framework for pro-... 

The filters should be located downstream of the coolers and should be equipped with a vent and orificed fill line to permit air removal prior to being put into service to prevent shocking the system. External lifts for the filter covers should be furnished if the covers are too heavy for an operator to safely handle. A suggested weight is 35 pounds, deferring however to operator safety. An adequate valved drain should be furnished for each filter body to permit easy removal of dirty oil and sludge. 

The isolation of certain mechanical equipment, e.g. conveyors, work on lifts, excavations, entry and positioning of cranes, isolation of various safety services , e.g. water or inert gas, stand-by power generation, water supply to sprinkler systems, compressed air for breathing apparatus. 

The horizontal plate filter requires attention on a regular basis to safety devices and automation features that accompany modern filters. The space above the filter should have a hoisting device and sufficient headroom to lift the entire disc stack and move it horizontally to a location adjacent to the filter tank. It is recommended to have a special rig that will hold the plate stack for maintenance since the bigger ones may reach a length 3 meters or more. Space must also be allocated for the cover which may be either if it is hinged or removed. 

Conventional Safety Relief Valve - A conventional safety relief valve is a closed-bonnet pressure relief valve that has the bonnet vented to the discharge side of the valve and is therefore unbalanced. The performance characteristics, i.e., opening pressure, closing pressure, lift and relieving capacity, are directly affected by changes of the back pressure on the valve. 

The pressure relief device used most often in refinery and chemical plant equipment is the spring-loaded, top-guided, high-lift, nozzle-type safety relief valve, which is illustrated in Figure 2. The spring is usually external and enclosed by a bonnet for weather protection, and the bonnet chamber is vented through an internal passage to the valve outlet. 

Pressure relief valves in liquid service (i.e., relief valves and safety relief valves) have the characteristic of progressively increasing lift with rising inlet pressure until the full open position is reached at about 1 % overpressure. This characteristic may vary between types and between makes. 

Figure 14. Capacity correction factors due to overpressure for relief and safety relief valves in liquid service. The curve shows that up to and including 25 percent overpressure, capacity if affected by the change in lift, the change in oriflce discharge coefficient and the change in overpressure. Above 25 percent, the valve is at fidl lift and capacity is affected only by overpressure.

The successes of the traditional approach have largely been obtained in the area of occupational safety, where statistical evidence is readily available concerning the incidence of injuries to individuals in areas such as tripping and falling accidents. Such accidents are amenable to behavior modification approaches because the behaviors that give rise to the accident are under the direct control of the individual and are easily predictable. In addition, the nature of the hazard is also usually predictable and hence the behavior required to avoid accidents can be specified explicitly. For example, entry to enclosed spaces, breaking-open process lines, and lifting heavy objects are known to be potentially hazardous activities for which safe methods of work... 

The theoretical maximum suction lift at sea level for water (14.7 psi) (2.31 fi/psi) = 34 ft. However, due to flow resistance, this value is never attainable. For safety, 15 feet is considered the practical limit, although some pumps will lift somewhat higher columns of water. WTen sealing a vacuum condition above a pump, or the pump pumps from a vessel, a seal allowance to atmosphere is almost always taken as 34 feet of water. High suction lift causes a reduction in pump capacity, noisy operation due to release of air and vapor bubbles, vibration and erosion, or pitting (cavitation) of the impeller and some parts of the casing. (The extent of the damage depends on the materials of construction.)... 

Conventional drill collars are made with uniform outside diameter and with slip and elevator recesses. Slip and elevator recesses are designed to reduce drill collar handling time while tripping by eliminating lift subs and safety clamps. However, the risk of drill collar failure for such a design is increased. The slip and elevator recesses may be used together or separately. 

Inspection by independent persons or bodies for safety purposes goes back to the middle of the nineteenth century. At that time, the focus of concern was the explosion of steam boilers, and this hazard was most prevalent in the textile industry. Consequently, a group of public-spirited individuals formed the Manchester Steam Users Association for the Prevention of Boiler Explosion. This body carried out boiler examinations and later added insurance as an inducement to the plant owners. By the beginning of the twentieth century steam and gas engines and electrical machines had been added, followed by lifts, cranes and hoisting machines. 

Repairs, renewals or alterations required to enable the hoist or lift to continue to be used with. safety-(a) immediately... 

Conflicting schedules with equipment such as lifting devices, safety apparatus, and mobile equipment. 

In addition to the general rules of the Health and Safety at Work, etc. Act 1974 there are specific requirements under the following legislation with respect to chains, ropes and lifting tackle ... 

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