This document specifies the safety requirements for horizontal directional drilling (HDD) machines (hereafter referred to as HDD machines) as defined in ISO 21467:2023 which are designed primarily for drilling through the earth in a mostly horizontal direction. This document is applicable to the following HDD machine types: portable HDD machines; pedestrian-controlled HDD machines; towed HDD machines; self-propelled HDD machines; ride-on HDD machines; remote-controlled tramming HDD machines; skid-mounted HDD machines; pit-launched HDD machines; surface-launched HDD machines. NOTE Some HDD machines can include a combination of types or characteristics noted above.