Welds on seams, joints, and penetrations of the hood must be what, according to NFPA standards?

According to NFPA 96 standards, welds on seams, joints, and penetrations of the hood must be smooth and cleanable to ensure the proper function and maintenance of the ventilation system. Smooth surfaces are essential because they minimize surface irregularities where grease and debris can accumulate, making it easier to clean and thus reducing the risk of fire hazards. A well-maintained hood reduces the likelihood of grease buildup, which is a significant fire risk in commercial cooking environments. Additionally, a cleanable surface promotes compliance with health and safety standards by ensuring that the ventilation system remains hygienic and effective in removing smoke, heat, and cooking vapors.

Other options do not meet these criteria: visible and loose joints may lead to inefficiencies and maintenance challenges, uneven surfaces can harbor grease buildup, and spot welded seams may not provide the required structural integrity and cleanliness needed for effective functioning.