angles building building-maintenance-unit color colors colour colours danger dangerous elevated equipment external features gondola gray grey Harness harnessed height heights high motorised paint painters painting perspectives platform platform-lift riggers rigging risks risky safety safety-harness surface surfaced surfaces surfacing suspended suspended-access textured textures up-high wall walls white work workers workmen aircraft anchored balloon cable checks circular control controlled duty-pilot engineers fabric filled flight-operation helium helium-balloon inspected inspections large limited mesh metal-cable metal-line monitored monitoring motion movement net passengers pilot piloted registered ride safe secure secured sights sightseeing Singapore tethered tourists views weather-limits wind-limits