| First author [ref.] | Design | Agent | Type of RPE | Effects of RPE |
| Muller-Wening [54] | Laboratory challenge Non-RCT study n=26 Exposure: 1 h, not quantified | Organic farm allergens | RPE with P2 filter: "Dustmaster" (n=21), "Airstream helmet" (n=4), "Airlite" (n=1) | Suppression of symptoms in 11 out of 26, reduction in 15 out of 26, but 4 required inhaled bronchodilator Reduction of the increase in airway resistance |
| Laoprasert [55] | Laboratory challenge RCT study with placebo n=9 Exposure: 1 h, quantified | Latex | Laminar flow HEPA–filtered helmet | Reduction of symptom score Reduction of the decline in FEV1 |
| Slovak [56] | Workplace exposure Non-controlled study n=8 Exposure: 6 weeks, not-quantified | Laboratory animals | Powered helmet respirator with AS-23-3 filter | Worsening of symptoms in 2 out of 8 (score not available) Peak flow variation at work in 2 out of 8 |
| Kongerud [57] | Workplace exposure RCT study n=19 workers with nonsevere disease Exposure: 2 weeks, not quantified | Aluminium pot room | AH60 Airsteam helmet | Reduction of symptom score in 10 out of 17 subjects (nonsignificant) Improvement in the mean peak flow values |
| Taivainen [58] | Workplace exposure Non-RCT study n=24 Exposure: 10 months, not quantified | Farming | Powered dust respirator helmet with P2 filter | No effect on respiratory symptoms with the exception of sputum, rhinitis symptoms, corticosteroid treatment, and number of sick leaves Increase in morning peak flow and reduced daily peak flow variability |
RCT: randomised controlled trial; HEPA: high-efficiency particulate arrest; FEV1: forced expiratory volume in 1 s.