Reliability and trouble-free work during the construction of buildings and structures is a task requiring a serious approach. It is no secret that the construction site is a territory of increased danger. And one of its most disadvantaged places is the space on which the crane is operated and moved. Prior to the commencement of all work related to the lifting of goods, when the zone of operation of the crane has already been determined, hazardous areas must be correctly calculated. It is there that potentially emergency factors operate, which can be either directly related to the operations being performed or exist independently of the work process.
The installed area of the crane. Danger zones - what applies to them?
Let's look at how you can calculate the boundaries of this potentially emergency territory. The boundary of the danger zone of the crane runs through the places over which it moves the building load. What applies to them? This is directly the area that the crane serves, but not only. To it should be added a distance equal to half of the smallest external dimensions of the cargo that will be moved by it.
Then - add here the minimum distance that the falling cargo is able to fly off, and, in addition, increase the size of the danger zone by the largest of the overall dimensions of this cargo.
The border of the zone to be serviced depends on the maximum departure of its boom (indicated as P (max.) Art.). To determine the smallest distance a load is able to fly off during a fall (we denote this value as P (exc.)), One should take into account the height of its rise.
To find out the height of a possible drop in cargo, we take the distance from the surface of the construction site to the bottom of the cargo, which is suspended from the crane boom. Slinging of goods is carried out using special devices called traverses, slings, etc.
Calculation according to the formula
For clarity, we give the formula. The calculation of the danger zone of the crane, according to it, looks like this:
Rkr (oz) = P (max.) Art. + 0.5 * P (min.) Gr. + P (ex.) + P (max.) Gr.,
where: Rkr (oz) - the calculated radius of the danger zone of the crane;
P (max.) Art. - maximum reach of his arrow in meters;
0.5 P (min.) Gr. - half the distance from the minimum of the cargo dimensions in meters;
P (exc.) - that is the minimum distance over which the transported cargo is able to fly off, (in meters);
P (max.) Gr. - the maximum of its dimensions in meters.
How are hazardous areas designated at a construction site
At the borders of those zones where hazardous production factors operate continuously, the installation of safety guards is necessary. Those areas that are potentially dangerous should be surrounded by signal fences and marked with safety signs.
Thus, when the crane operating zone is determined , hazardous areas on the ground are marked with the help of signs established in accordance with GOST that carry a warning function. They should be placed so that the borders are clearly visible. During the dark, they must light up.
They are installed on special racks, which must be securely fixed to avoid falling from walking people and passing vehicles. Where the crane’s operating area ends, hazardous areas can be adjacent to people’s passages (roads and footpaths). In such areas, warning signs are also required.
It is unacceptable to place sanitary facilities, recreation places, walkways for people, that is, any zones of permanent or temporary stay of workers in a dangerous territory.
Other prerequisites
If any work should be carried out in the danger zone whose nature is not related to the planned ones, such an action must necessarily be accompanied by the issuance of a work permit.
If the construction site is organized in such a way that on the side where the building is being built, there are no rail fences for the crane, any of the doorways facing him must be closed tightly.
If the crane is equipped with a magnet or a grab, the zone of its operation must be marked with the corresponding warning signs in accordance with GOST and blocked with signal boundaries.
Where such a crane works, people are forbidden to be. Technical maintenance by auxiliary personnel is allowed only during breaks between work intervals when a magnet or grab occupies a stable position on the ground.
All crane operators and auxiliary workers are required to be instructed in safety procedures when carrying out such work. The crane operator is supposed not only to know the definition of the dangerous zone of the crane and be able to establish its boundaries, but also to understand the routes of movement of the magnet and grab.
What cranes should be equipped with
If there is no annular current collector between the individual parts of the crane - rotary and non-rotary - it is necessary to have a rotation limiter.
It is necessary to provide a safety device, the function of which is to automatically stop the operation of the freight trolley in the event of a trolley cable break.
The crane must be equipped with an audio signal, the tone of which does not coincide with the automobile.
A voltmeter is required, as well as a time meter that was worked out by the cargo winch or by the crane itself, and, in addition, a cable drum.
What determines the safety of the crane
Much here decides the correct slinging of goods and termination of the rope. It is attached to the metal parts of the crane using various types of loops, couplings, knots, wedge clamps. The loops at its ends are made by braiding, preventing flattening and grinding.
Splicing the ropes of a tower crane is strictly prohibited. The load is attached with it to the lifting mechanism thanks to special devices in the form of blocks, drums, chain hoists.
Using blocks, the load is raised and lowered, the chain hoist is a system of interconnected movable and fixed blocks. The drums in the hoisting mechanisms look like hollow cylinders with helical grooves on the surface for the convenience of laying the rope and reducing its wear.
Tower cranes - why are accidents frequent?
Unlike other types of lifting mechanisms, tower cranes are relatively often collapsed. The reason for this is their design features. The track of the path along which it moves, as a rule, has a width (i.e. inter-rail distance) of not more than six meters. The base of the crane (we are talking about the gap between the axles of its undercarriage, which are located on the same rail) is also insignificant and, as a rule, does not exceed the same distance.
Its height is quite large, and from this the tower crane is very sensitive to wind loads. The same applies to other conditions of its operation. With strong gusts of wind, the crane can fall even when not in use. To prevent this, anti-theft captures are used.
The drops of cranes, the frequency of which is quite high, are practically not affected by carefully observed safety requirements. Statistics found that most often this happens with those of them that use rail tracks to move.
What does it depend on
Practitioners have long suspected that the cause of high accidents was the imperfection of the fundamentals of the rail track. As its main factor, implied uneven compaction of the soil under each of the rails. Back in the 70s of the last century, experiments were carried out to control the density of rail bedding, but they did not have a serious impact on the actual state of affairs - cases of falling cranes continued.
Experienced crane operators believe that a fall can be caused by swinging. The flexibility of the soil mass under one of the rails can increase due to tectonic disturbances with increasing seismic load. As a result, the crane loses its reliable support and at any displacement of the center of gravity can tip over.