Cribbing (rescue)

In vehicle extrication and urban search and rescue, cribbing is the misc. size wood used to stabilize an object, for example so that trapped victims can be safely removed. It is commonly used to stabilize overturned cars, and debris within collapsed buildings. Cribbing is often used in conjuntion with other stabilization equipment, such as pneumatic or hydraulic shoring. Cribbing is also used in sub-surface mining as a roof support. Cribbing has largely been replaced by hydraulic shoring in modern mining aplications.

Cribbing was also used in the construction of the Cariboo Wagon Road to help stabilize it in the steep Fraser Canyon

Some forms of cribbing can also be used on movie sets and production sites for stabilizing dolly tracks, platforms, and various temporary structures when quick setup times are needed.

tability

The stability of a crib is effected by a variety of factors: the material used (often a soft wood which gives audible warnings before failure), the number of contact points between the crib and the supported surface, the ratio of the footprint of the crib to its height, and the area of contact made between the crib and the ground and supported surface.

Materials

Cribbing is usually accomplished with blocks of wood, often 4"x4" or 6"x6" and 18"-24" long. Soft woods, like spruce and pine are often preferred because they crack slowly and make loud noises before completely failing, whereas stiffer woods may fail explosively and without warning.

Cribbing may also be made out of plastic, which unlike wood is not susceptible to rot or corrosion from fluids the cribbing may come in contact with (e.g. oil, gasoline, hydraulic fluid).

Cribbing equipment is normally of three varieties: rectangular blocks, wedges (also called shims), and "step chocks" (large wooden chocks constructed of wood of different lengths). Blocks are the bread and butter of cribbing and will be used in most cribbing evolutions. Shims are used to snug up contact between the crib and supported object or change the direction of the crib (tilt). Step chocks are often used as a quick solution for stabilizing vehicles on all fours or to quickly increase the height of a crib.

Methods

Cribbing structures are often categorized by shape. Different shapes of cribbing structures are chosen depending on the area available and the point being cribbed to.

A box crib is the most common method of cribbing, and is constructed by arranging pairs of wood in a regular log-cabin style to form a rising rectangular frame.

A traingle or A' crib is similar to the box crib, except it resembles a triangular prism instead of rectangular.

A parallelogram crib resembles a diamond prism.

A "'tilted tower" crib is a box crib in which pairs of shims are used to change the direction of the rising structure, resulting in a curve. Curving a crib must be done in moderation and is only advisable for structures at sharp angles to the ground.

Cribbing can be done in conjunction with lifting of an object. The rule is lift an inch, crib an inch. In vehicle extrication, this lifting may be accomplished with jacks, lifting air bags, or hydraulic rescue tools.

External links

* [http://www.builderbill-diy-help.com/low-tech.html Using box cribs] A description of two men lifting a demountable building off a truck and placing it on prepared foundations by hand.