TOKYO -- At least 70 percent of earthquake shock absorbers for buildings shipped by a leading manufacturer and its subsidiary potentially do not meet quality standards set by the government or clients, the manufacturer, which earlier admitted to fabricating quality inspection data, told the Mainichi Shimbun.
Nearly 1,000 buildings nationwide, including Tokyo Skytree tower, Tokyo Station and prefectural government buildings in Tokyo, Osaka and Aichi, use products made by leading shock absorber manufacturer KYB and its subsidiary Kayaba System Machinery Co. (KSM).
According to KYB Corp., the data cheating is suspected to have started in 2000, and a total of 10,369 such absorbers -- also called seismic isolation oil dampers -- have been shipped. Of the total, 7,550 products that did not or are suspected of failing to meet the required standards were received at 903 facilities. As many as 20,779 stabilizers, or vibration control dampers, were sent to customers, and 3,378 dampers of problematic quality were used at 83 buildings.
These products are in use at 986 facilities nationwide, but 576 of them lack inspection data and KYB is in the process of investigating them.
Seismic isolation dampers are designed to weaken earthquake jolts and reduce the seismic shaking felt by the buildings. When damper firmness is greater than the standard, buildings tend to shake more. When they are lower than the standard, dampers soften and buildings oscillate with greater amplitude. The Ministry of Land, Infrastructure, Transport and Tourism sets a margin of plus and minus 15 percent from the standard figure as acceptable, while customers generally seek a 10-percent margin.
A sampling survey by KYB of remaining data on shipped products indicated that quality deviation for isolation dampers was 16.0 percent to 42.3 percent above the ministry standard. As for vibration control dampers, for which no government standard exists, their quality varied between 17.9 percent below the standard sought by customers and 20.5 percent above it.
The ministry says the problem dampers can withstand earthquakes with an intensity of around a maximum 7 on the 7-point Japanese seismic scale, but still instructed KYB to replace the products.
The dampers of non-compliant quality were produced by KYB from 2000 to 2007, and by its subsidiary KSM from 2007 onward. After KYB reported the data cheating on Sept. 19, ministry officials conducted an on-the-spot inspection of a KSM factory in the city of Tsu in the central Japan prefecture of Mie on Oct. 10, and checked the company's quality control arrangements.
(Japanese original by Norihito Hanamure, City News Department)