HSE stats are pretty meaningless for the average organisation which maybe employs a few hundred people at most! If you divide the HSE data by 1000, you get the rate per 100 employees - and everyone can envisage what 100 people look like! Thus the average construction figure per hundred is about 0.5, or 1 reportable every 2 years. If you continue to have one reportable every year for your 30 employees, your rate is indeed much higher than average, 3.3 per 100 employees. In its guide on reporting, IOSH recommends this approach. 100 employees also work ~200,000 hours per year, so you can directly compare the numbers with US-based data which is per 200,000 hours.