Supporting pin at boom of a Con ’ c pump car broken to hit the victim (Serious Accidents in Construction) Construction The copyright to this material belongs to the Korea Occupational Safety and Health Agency. Unauthorized use and distribution are prohibited. If an individual uses this for non-commercial purposes, the Korea Occupational Safety and Health Agency must be cited as the source. A corporation using this material must obtain permission from the Korea Occupational Safety and Health Agency first. Using this material without prior permission will be considered copyright infringement, and legal action may be taken. 건설분야 - 교육자료 미디어개발

Table of Contents I. Fatality Overview II. Site Overview III. Fatality Description IV. Fatality Cause V. Precautions

Think it over! Find out the Hazard Points in the figure below.

Date & Time: 13:35, December 5, 2007 (Wednesday) Place: new constructions site of ○○ neighborhood facilities Victim: 2 concrete workers of a subcontractor (males/44) While the victim was pouring concrete on floor slab on the 1 st floor above ground, A hydraulic cylinder-supporting pin at a boom of the Con ’ c pump car was broken causing the falling of the boom to hit the victim to death. Supporting pin at boom of the Con ’ c pump car broken to hit the victim 1. Fatality Overview Site Overview New construction of neighborhood facilities (2 stories above ground and 1 below, 1 building) site - 1 st floor structure (concrete pouring) working was under way (overall process rate was 15%)

At about 07:00, 11 workers of a subcontractor went to the site. The victim and co-workers started enforcing form and supporting post to pour concrete in the morning. ※ That day, they were supposed to pour concrete on pillars on the first basement and floor slab on the first floor above ground. (The amount was approx. 151 ㎥ ). At about 13:00, a concrete pump car had arrived in the site and checked for outrigger, boom angle, and working radius. The pump car operator found that the hoses were not enough to cover the area and added a hose (diameter: 145MM, length: 7.2M) to the end of boom end hose (length: 3.5M). ※ The pump car’s maximum horizontal working radius was 32M. However, maximum distance for concrete pouring was 38M. Supporting pin at boom of the Con ’ c pump car broken to hit the victim 3. Fatality Description

The pump car got ready and 5 co-workers including the victim poured concrete on the floor slab on the 1 st floor above ground and 3 co-workers checked for form and supporting post in the 1 st basement, the other three co-workers dismantled outer wall form in the basement. ※ The concrete worker ’ s job allotment - Victim 1 (injured): compacting concrete using a vibrator - Victim 2 (injured): assisting by holding the vibrator engine - 2 co-workers: holding pump car hose while concrete pouring - 1 co- worker: flattening concrete using a iron rake Supporting pin at boom of the Con ’ c pump car broken to hit the victim concrete pump car end hose extended hose

For deformation prevention and balance of entire structure, they conducted overall concrete spray with the first 2 concrete mixers. At about 13:35, they lowered the boom and two co-workers pulled the extension hose toward outer wall to pour concrete into the staircase wall in the quoin. During that process, a hydraulic cylinder supporting pin (Φ80 ㎜ ) connecting the 1 st and 2 nd section booms was fractured causing lowering of the booms. The 4 th section boom hit the victims. 1 victim was taken to the hospital. He died during medical treatment and the other victim injured the left arm. Supporting pin at boom of the Con ’ c pump car broken to hit the victim

Supporting pin at boom of the Con ’ c pump car broken to hit the victim

Supporting pin at boom of the Con ’ c pump car broken to hit the victim [Fatality Site]

Supporting pin at boom of the Con ’ c pump car broken to hit the victim [4th boom that hit the victims]

Supporting pin at boom of the Con ’ c pump car broken to hit the victim [Broken part (connections between 1st and 2nd boom)]

Supporting pin at boom of the Con ’ c pump car broken to hit the victim [Broken supporting pin (Φ80 ㎜ )]

Supporting pin at boom of the Con ’ c pump car broken to hit the victim [Extended hose (end hose (standard) + added hose)]

Supporting pin at boom of the Con ’ c pump car broken to hit the victim [Broken supply hose and boom (4th boom)]

No observance of safety regulations - You should understand the structure of the equipment and observe safety regulations to prevent booms and arms from breaking while operating a pump car. However, the safety regulations were not observed. Unprepared work plan - You should prepare work plan of operating path and proper working method considering kind and capacity of an equipment. However, the work plan was not prepared. Supporting pin at boom of the Con ’ c pump car broken to hit the victim 4. Fatality Cause

※ Opinion of non-observance of safety regulations Ⅰ. Cause analysis of breaking of hydraulic cylinder supporting pin (Φ80 ㎜ ) 1. safety Inspection Supporting pin at boom of the Con ’ c pump car broken to hit the victim ⇒ For safety inspection, spread booms horizontally (in as straight line) and fill concrete into the supply pipe of the boom and add load of 180kg (value considering safety ratio) on boom end. - Check for damage of structural member such as booms and hydraulic cylinder to inspect safety. ∴ Allowable moment of broken parts of the supporting pin (A point) by the above method Ma = 0.18ton × 23.3m = 4.19 ton/m A: supported broken part

2. Opinion of additionally applied moment to the broken part (A point) during operation. Supporting pin at boom of the Con ’ c pump car broken to hit the victim 1) Examination of additionally applied load to point C ⇒ Simplifying as the following figure; concrete pump car extended hose load applied to point C (P)

⇒ Supposing that concrete is full into a hose [end hose + extension hose, diameter: 145mm, length: 10.7M], the vertical load (P) applied to C point is P = hose cross section × hose length [vertical hose 4.7M + horizontal hose 3M] × concrete specific gravity = (π× (0.145m)/4) × 7.7m × 2.3ton/ ㎥ = 0.29 ton 2) Calculation of moment distance (L) applied to A point ⇒ 8.7 CosB CosC = ① ⇒ 8.7 SinB = 23.3 SinC ② According to ①, ② ; L: 22.8M 3) M= P × L =0.29ton × 22.8m = 6.67 ton/m 3. Examination of safety of hydraulic cylinder supporting pin [Check for moment on the broken part rather than comparison of simple load (P) applied to boom end] ⇒ It should be allowable moment (Ma)> applied moment (M), however, ⇒ Ma (4.19 ton/m) < M (6.67 ton/m). Therefore, it is not safe. Accordingly, safety regulations on a pump car was not observed. Supporting pin at boom of the Con ’ c pump car broken to hit the victim

Ⅱ. Opinion of applied load by extended pump car hose 1. To extend a hose to pump car for concrete working; Supporting pin at boom of the Con ’ c pump car broken to hit the victim ⇒ As shown in above figure, we judged that extension hose was vertically down not applying to much vertical load (P) of concrete applied to the extension hose to point C. concrete pump car extended hose

2. To pour concrete in an area exceeding working radius of pump car boom (staircase wall) Supporting pin at boom of the Con ’ c pump car broken to hit the victim ⇒ As shown in above figure, they pulled extension hose horizontally to lay down the booms causing too much holding force and load (P) of concrete weight on extension hose into boom end (point C ). concrete pump car extended hose

Ⅲ. Maximum allowable extension length of pump car hoses ⇒ Maximum extension length of a hose can be added to concrete boom end is limited to Lmax = 4M based on inspection of safety regulations as shown in the figure (structure at which various structural members such as booms can bear load of 180kg at the boom end). Supporting pin at boom of the Con ’ c pump car broken to hit the victim A: broken part

Observation of safety regulations - When you use construction vehicles (pump car), you must observe safety regulations and maximum allowable load considering the equipment structure to prevent boom and arm from breaking. Preparation of work plan considering proper working process - To operate construction vehicle (pump car), you should set a work plan of operation path and proper working process considering the kind and capacity of equipment. Supporting pin at boom of the Con ’ c pump car broken to hit the victim 5. Precautions

Thank You.