Under the agreement, Neptune will pay an initial $4.5 million along with a three-year earn out period based on EBIT (earnings before interest and tax) performance for Access.
The acquisition will be funded by cash raised through the company's $61 million share placement completed late last year.
Access uses rope access, lightweight staging and tension netting to provide safe solutions to difficult access problems.
The company has annual revenues of about $4 million and EBIT of $1 million.
"Access Management represents a young, dynamic company whose innovative services could be seamlessly assimilated into those of the Neptune Marine group that continues to consolidate its position in the global marketplace," Neptune managing director Christian Lange said.
Neptune's move to buy Access is just the latest in the company's string of acquisitions.
Earlier this month the company completed its acquisition of Fremantle-based Sea-Struct, which manufactures, supplies and installs pipeline and cable stabilisation protection and erosion control products for the subsea oil and gas sector and the broader marine services market.