Which type of hard hats are designed to protect the top of the head only?

Type I hard hats are specifically designed to provide protection from impacts to the top of the head. These hats are typically used in situations where falling objects are not a primary concern, but rather where there is a risk of the head striking fixed objects overhead. This type of hard hat is often used in industrial settings and construction sites where workers may be exposed to overhead hazards, but the design focus is primarily on protecting the crown of the head.

In contrast, Type II hard hats are designed to offer protection from both the top and side impacts, making them suitable for environments where lateral forces might be a concern. Type III and Type IV hard hats, while not commonly referenced, generally refer to additional design specifications for multi-directional or specific usage that features additional protective characteristics. Therefore, the focus on top-of-the-head protection makes Type I the correct choice for this question.