These additional drivers may simply be a sudden loss of bal- ance, but could also be some physical attributes of the work area。

Ground or water contamination Class 1 (existence) Existence of water, hard pavement or sharp material   Class 3 (vicinity)

Driver: Anchorage Points  (APs)

Description: Designing APs to facilitate installation of fall arrest systems around working platforms and tanks, roofs and bridges drives down the probability of fall

Rules to check

Facilities that need periodic maintenance Class 1 (existence) Anchorage points suitable for hooking lanyards Class 3 (spotting)

Driver: Hazard Zones  (HZs)

Description: Risk of falling objects was driven up both in probability and consequences when workers were allowed to pass HZs under potential falling objects

Rules to check

Elevation of material deposits Class 1 (geometry)

For example, at July 2011, a welder fell 118 meters to his death,

after he lost his balance and unluckily crossed a small gap in the

safety net underneath。 Although the reason why he had unhooked his lanyard and hooked it again to his own belt at that moment was

Restrictions of access to areas underneath the deposits

Guardrails or covers provided over openings and edges

Class 1 (existence)

Class 3 (spotting)

never discovered, the temporary minor gap in the safety net cer- tainly played a key role in driving the risk of his fall up。 Table 6 demonstrates such attributes observed to contribute to the studied injuries。

4。2。Working with machinery

Unsafe machinery operation will result in collisions, electrocu- tions, burns, tipping, rollovers, and being crushed, pinned, and entangled in the moving parts。 This research showed that more than one fifth of the fatalities (17 out of 79) caused by    engineering

Clearance of deposits from edges Class 3 (spotting)

Stability of roof material Class 3c (advanced technical)

vehicles were related to the concept of Design for Safety。 Many machinery accidents took place as a result of a few initiating events, only one of which was unsafe machinery operation。 For example, in July 2011, a truck mixer hit a five story building caus- ing it to collapse, with two workers killed and five injured。 The building was being topped out and no lateral bracing was installed before the day of accident。 If the construction project was so sched-

452 H。 Malekitabar et al。 / Safety Science 82 (2016) 445–455

uled that the shear-walls would have been assembled at the right time, a simple crash would never make the whole building col- lapse。 Some accidents that may be seen as a crash or mechanical failure can also be anticipated at the design phase by observing instructions provided by the equipment manufacturer。 Table 7 summarizes the most frequent drivers influencing the occurrence of equipment accidents (see Fig。   2)。

4。3。Working in confined spaces

OSHA 1910。146(b) defines a confined space as a temporary workplace   with   limited   means   of   entry   or   exit,   which   can

Table 7

Drivers for the risk of ‘‘unsafe  operation”。

Drivers and rules Rule class and  type

of check

Fig。 2。  Wheel loader tipped over due to insufficient roadway  width。

Driver: Equipment Properties  (EPs)