Shima says New Zealand's poor health and safety record has prompted the law change which includes stiff new penalties for those who fail to carry out their responsibilities.
"Every year in this country around 52 people die while on the job. Thousands more are seriously hurt and between 600 and 900 people die from work-related diseases," Shima explains.
In the Bay of Plenty alone, WorkSafe New Zealand figures show 18 people have died in the last five years and 1643 workers suffered serious harm - 67 of those cases having already occurred this year.
"This new law is designed to help reduce the number of serious work-related injuries and deaths in New Zealand by at least 25 per cent by 2020.
"What this means is employers must involve their staff in reviewing and identifying ways to manage workplace hazards. And they must do it now. Any injuries or deaths that occur after April 4 will see companies - and individuals - held liable under the new law."
Rather than feel daunted by the task ahead, Shima says the HSWA is a great opportunity for workers to get involved and help shape their company policies.
"Employers should start by reviewing their health and safety system. Get staff involved and talk about what's going on. You might not realise what all the hazards are but people on the shop floor may well know better than anyone."
Shima says the new law puts the onus on two main groups - 'PCBUs' and 'Officers'.
"PCBU stands for 'person conducting a business or undertaking. In most cases it will be a company or organisation but individuals, like sole traders, can be PCBUs as well.
"Officers are people such as directors, chief executives and people who make operational decisions that influence a large part of the business. They are effectively WorkSafe NZ's new policemen and have to ensure the PCBU is effectively looking after the health and safety of its workers."
Shima says 'officers' need to become health and safety champions and lead their company culture. "Don't accept unsafe practices or ignore people doing obviously dumb things like standing on chairs with wheels to reach something."
Health and safety training is available through various industry bodies, so check to see what courses and funding are available.
"The best policy is to get health and safety right to begin with. But if a serious accident does occur, it's important to conduct a proper investigation immediately and that's where outside expertise are really valuable."
Shima has a wealth of experience conducting health and safety investigations and is keen to help local businesses understand their new responsibilities.
"It's about continuous improvement. Many businesses started off with a hiss and a roar but haven't looked at their health and safety policies for years. It needs to be a living document - something that people look at, have input and talk about. Health and safety needs to be embedded into everyday practices and this new law is designed to achieve that."