Monday, 14 September 2015

Balustrade and Barrier Heights the reasoning?

{Previously posted in LinkedIn group I created: Pre-Engineered manufactured structural Building products, and have since shut down. It having a membership of 30 people. Most of these people also in my group Pre-Engineered Manufactured Building Systems Group which has over 2000 members.}

The industrial platforms code (1992) differentiates between guardrails (900<h<1100) and handrails (800<h<1000), whilst the Building code of Australia (BCA) is not so clear. If a guardrail is too low then people can topple over, if it is too high then people can fold and fall under it. So a single rail has to be just right height to function, but population heights are distributed: and consequently it is not entirely feasible to have a single rail that will function for all people. Similarly if a handrail is too low it is uncomfortable to use, if it is too high it cannot be reached. The BCA does not limit the height of a handrail it only sets a minimum.

It is therefore preferable that a more complete barrier is formed with infill below the guardrail. In industrial applications that is typically just a kneerail. In other applications additional horizontal rails are considered a climbing hazard, so infill is typically vertical rails. Vertical rails also provide some function as grabrails/handrails for children who cannot otherwise reach a handrail. However infill below the guardrail only prevents shorter people from folding and falling under the guardrail, it won't stop taller people toppling over.

The height set for the barrier has to be greater than the centre of gravity of the human body, not equal to, but that varies from person to person. At the end of the day a code compliant guardrail cannot stop someone falling over. A barrier really needs to be infilled between floor and top edge, and the top edge needs to be up around the 95th percentile shoulder height of the population: so that not relying on a fine balance in the range of centre of gravity.

AS1657:2013 seems to have become as confused as the BCA, with respect to differentiating between guardrails and handrails. The typical industrial gurardrail was set 1000mm height because handrail and guardrail were one and the same component: and 1000mm met both the guardrail and handrail height requirements. In terms of AS1428 however such guardrail may be considered too high to be a handrail.

The height set is a matter of economy and works most of the time for normal circumstances. Glass panel and other solid panel infills, lack the additional rails for grip in a fall that vertical infill rails provide. From metric data handbook 95th percentile shoulder height is 1528mm, so top edge around 1550mm is likely a better barrier to falling. Architects are increasingly opting for 1200mm to 1800mm barrier heights. The latter seems like the better option, full height walls seem even better.

The point is that the function of the guardrail is not to prevent falls but to minimise falls, if wish to prevent falls then a more appropriate barrier is required.