The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit of 5 mg/m3 over a 15-minute period.
ðə nˈæʃənəl ˈɪnstɪtˌuːt fɔːɹ ˌɑːkjʊpˈeɪʃənəl sˈeɪfti ænd hˈɛlθ nɪˈɑːʃ hɐz sˈɛt ɐ ɹˌɛkəmˈɛndᵻd ɛkspˈoʊʒɚ lˈɪmɪt ʌv fˈaɪv ˌɛmdʒˈiː slˈæʃ ˈɛm θɹˈiː ˌoʊvɚɹ ɐ fˈɪftiːnmˈɪnɪt pˈiəɹɪəd.