Inspectors from safety and regulatory bodies have arrived at the site of the fatal fertilizer plant blast in West, Texas, but records show that the most important watchdogs had not visited in the past five years.

According to data from the Texas Commission on Environmental Quality (TCEQ) and the Environmental Protection Agency (EPA), the last documented visit to the West Fertilizer Company occurred in late 2007, as a follow-up to a complaint of an odour coming from the plant. The Occupational Safety & Health Administration (OSHA) – a body tasked with making sure America's 7 million workplaces are safe for employees – has not made a site visit since 1985.

An industrial chemicals expert with 35 years' experience in the field told the Guardian that the lack of inspections was to expected, given that OSHA was severely "undermanned and overloaded".

On the occasions that the West Fertilizer Company was inspected, safety violations were identified. The TCEQ said the factory was required to have two permits – the first for two 12,000-gallon anhydrous ammonia storage tanks, and the second for the loading and storage of dry fertilizer materials.

But because the plant was built in 1962 – prior to state and federal requirements regarding air contaminants – it was exempted from having to have these permits until 2004. It was only in 2006, two years after its so-called "grandfathering" had elapsed, that regulatory bodies stepped in. Following a complaint from a member of the public in June 2006, regarding odour coming from the site, inspectors noticed that the plant's grandfather exemption had lapsed, and issued a notice of violation. The West Fertilizer Company applied for the relevant air permit in December 2006.

In the same year, the EPA fined the factory for a number of deficiencies regarding its risk-management programme (RMP). Inspectors found that not only had the company neglected to update its plan in a timely fashion, it had also failed to document how it intended to address safety concerns. A fine of $2,300 was imposed.

Since 2006, no complaint had been made against the factory to the two bodies and it complied with requirements to submit a new RMP in 2011. But between 2006 and 2013 there were no inspections by either the EPA or the TCEQ.

The OSHA – the federal body tasked with making sure that working conditions comply with safety standards – has not visited the fertilizer factory for 28 years, despite the potentially hazardous nature of the chemicals stored there. On that visit, in 1985, it identified one serious and two other violations. The company was fined just $30.

Last year, the US Pipeline and Hazardous Materials Safety Administration, which regulates the transportation of hazardous material, fined West Fertilizer $10,000, for failings that included planning to transport anhydrous ammonia without adequate security. The company agreed to take corrective action and paid a reduced fine of $5,250.

Bob Johnson, a recently retired industrial chemist who spent 35 years working for ICI and its subsidiaries, said he was not surprised by the lack of inspections. "In my experience, OSHA is overloaded and undermanned. They cannot cope, they cannot possibly do what they are supposed to do – they do not have the boys on the ground," he said.

The OSHA covers 7 million worksites in the US but has just 2,000 inspectors nationwide. Under its current funding, it can only conduct 40,000 inspections every year.

The sequester will hit the OSHA further. Under the automatic spending cuts – caused by a failure to reach compromise in Congress – the agency will have its budget cut by 8.2%, about $50m.