A minimum 3-board working system, together with a solitary guardrail, is in place when the scaffold is assembled or taken apart. http://hpmu.edu.vn/hpmu/index.php?language=vi&nv=users&nvvithemever=t&nv_redirect=aHR0cDovL21vemlsbGFiZC5zY2llbmNlL2luZGV4LnBocD90aXRsZT1ob3VtYW5ubG9yZW50c2VuNjcwOA