abandoned
alert
arrow
art
attention
background
black
bright
caution
closeup
danger
dangerous
decay
electric
electrical
electricity
energy
fence
galvanized
gray
high
industrial
industry
label
metal
metallic
new
nobody
notice
old
power
powerplant
risk
safety
security
shock
sign
standard
steel
surface
symbol
technology
triangle
volt
voltage
wall
warning
white
yellow